# UVB

For alternative meanings, see ultraviolet (disambiguation)

Ultraviolet (UV) light is birds.

UV light is found in chemical bonds in molecules, even without having enough energy to ionize atoms.

Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV on the skin, called vitamin D (peak production occurring between 295 and 297 nm) in all organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human health.

## Discovery

The discovery of UV radiation was associated with the observation that [4]

The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann.[5]

## Origin of the term

The name means “beyond violet” (from Latin ultra, “beyond”), violet being the color of the shortest wavelengths of visible light. UV light has a shorter wavelength than violet light.

## Subtypes

The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The ISO standard on determining solar irradiances (ISO-21348)[6] describes the following ranges:

Name Abbreviation Wavelength range
(in nanometres)
Energy per photon
(in electronvolts)
Notes / alternative names
Ultraviolet UV 400 – 100 nm 3.10 – 12.4 eV
Ultraviolet A UVA 400 – 315 nm 3.10 – 3.94 eV long wave, black light
Ultraviolet B UVB 315 – 280 nm 3.94 – 4.43 eV medium wave
Ultraviolet C UVC 280 – 100 nm 4.43 – 12.4 eV short wave, germicidal
Near Ultraviolet NUV 400 – 300 nm 3.10 – 4.13 eV visible to birds, insects and fish
Middle Ultraviolet MUV 300 – 200 nm 4.13 – 6.20 eV
Far Ultraviolet FUV 200 – 122 nm 6.20 – 10.16 eV
Hydrogen Lyman-alpha H Lyman-α 122 – 121 nm 10.16– 10.25 eV
Extreme Ultraviolet EUV 121 – 10 nm 10.25 – 124 eV
Vacuum Ultraviolet VUV 200 – 10 nm 6.20 – 124 eV

Vacuum UV is so-named because it is absorbed strongly by air, and is therefore used in a vacuum. In the long-wave limit of this region, roughly 150 – 200 nm, the principal absorber is the oxygen in air. Work in this region can be performed in an oxygen-free atmosphere (commonly pure nitrogen), avoiding the need for a vacuum chamber.

## Sources of UV

### Natural sources and filters of UV

Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC is blocked by dioxygen (from 100–200 nm) or by ozone (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone and most of it reaches the ground.

The sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm (see false color photograph of the Sun in extreme ultraviolet beginning this article). Extremely hot stars emit proportionally more UV radiation than the Sun. For example, the star R136a1 has a thermal energy of 4.57 eV, which falls in the near-UV range (optically, such stars appear blue-white rather than violet).

[9]

Since with the Sun at zenith the Earth's air and ozone layer allows passage of a total of 32 watts/m2 (ground UV power) out of a vacuum value of about 140 watts/m2 (i.e., 23%) of Sun's UV light, this is equivalent to a minimal atmospheric blockage of 77% of the Sun's UV. However, most of the Sun's UV that is blocked by Earth's atmosphere lies in the shorter UV wavelengths. The figure rises to 97–99% of the Sun's UV radiation at the average mixture of other Sun angles encountered through the day.[10]

The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air. Of the ultraviolet radiation that reaches the Earth's surface, up to 95% is UVA (the very longest wavelength),[11] depending on cloud cover and atmospheric conditions.

Ordinary glass is partially [14]

### Artificial sources of UV

#### “Black lights”

Two black light fluorescent tubes, showing use. The top is a F15T8/BLB 18 inch, 15 watt tube, used in a standard plug-in fluorescent fixture. The bottom is an F8T5/BLB 12 inch, 8 watt tube, used in a portable battery-powered black light sold as a pet urine detector.

A black light is a lamp that emits long-wave UVA radiation. Some types filter out visible light by using selective-pass wood's glass. Fluorescent black light lamps employ UVA phosphor blends and constructed in the same fashion as normal fluorescent lights. BLB type lamps use filtering glass which is deep-bluish-purple optical filter which blocks almost all visible light above 400 nanometres.[15] The color of such lamps is often referred to in the lighting industry as “blacklight blue” or “BLB”, to distinguish them from UV lamps used in “bug zapper” insect traps, that do not have the optical filter coating. These are designated “blacklight” (“BL”) lamps. The phosphor typically used for a near 368 to 371 nanometre emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+), whereas the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate (BaSi2O5:Pb+). “Blacklight Blue” lamps peak at 365 nm.

A black light may also be formed, very inefficiently, by simply using mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass are also made, in ratings up to 1 kW, used mainly for theatrical and concert displays.

Some UV fluorescent bulbs specifically designed to attract insects use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Plain glass blocks less of the visible mercury emission spectrum, making them appear light-blue to the naked eye. These lamps are referred to as “blacklight” or “BL” in most lighting catalogs.

#### Short wave ultraviolet lamps

9 watt germicidal UV lamp, in compact fluorescent (CF) form factor

Lamps which emit short wave UV light are also made. citation needed]. The quartz tube is doped with an additive to block the 185 nm wavelength. These “germicidal” lamps are used extensively for disinfection of surfaces in laboratories and food processing industries, and for sterilizing water supplies.

Standard bulbs have an optimum operating temperature of about 30 degrees Celsius. Use of a mercury amalgam allows operating temperature to rise to 100 degrees Celsius, and UVC emission to about double or triple per unit of light-arc length. These low-pressure lamps have a typical efficiency of approximately thirty to thirty-five percent, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–35 watts of total UV output. UVA/UVB emitting bulbs also sold for other special purposes, such as reptile-keeping.

#### Gas-discharge lamps

Specialized UV gas-discharge lamps are sold, containing a variety of different gases, to produce UV light at particular spectral lines for scientific purposes. Argon and deuterium lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride.[16] These are often the light sources in UV spectroscopy equipment for chemical analysis.

#### Ultraviolet LEDs

Light-emitting diodes (LEDs) can be manufactured to emit light in the ultraviolet range, although practical LED arrays are very limited below 365 nm. LED efficiency at 365 nm is about 5–8%, whereas efficiency at 395 nm is closer to 20%, and power outputs at these longer UV wavelengths are also better. Such LED arrays are beginning to be used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. Power densities approaching 3 W/cm2 (30 kW/m2) are now possible, and this, coupled with recent developments by photoinitiator and resin formulators, makes the expansion of LED-cured UV materials likely.

A 380 nanometre UV LED makes some common household items fluoresce.

#### Ultraviolet lasers

UV solid-state lasers can be manufactured to emit light in the ultraviolet range.

The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam which is mostly UV. The strongest lines are at 337.1 nm wavelength in the ultraviolet. Other lines have been reported at 357.6 nm, also ultraviolet. (This laser also emits weaker lines in blue, red, and infrared)

Direct UV-emitting laser diodes are available at 375 nm.optical storage).

## Detecting and measuring UV radiation

Ultraviolet detection and measurement technology can vary with the part of the spectrum under consideration. While some silicon detectors are used across the spectrum, and in fact the US NIST has characterized simple silicon diodes[19] that work with visible light too, many specializations are possible for different applications. Many approaches seek to adapt visible light-sensing technologies, but these can suffer from unwanted response to visible light and various instabilities. A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Ultraviolet light can be detected by suitable photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are available.

### Near and medium UV

A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers.

Between 200 and 400 nm, a variety of detector options exist. Photographic film detects near UV coming from blue sky as “violet” as far as the glass optics of cameras will permit which is usually to about 350 nm. For outdoor film photography, in fact, slightly yellow UV filters are often standard equipment in order to prevent unwanted bluing and overexposure by UV light that the eye does not see (these filters are also convenient lens scratch protectors). For photography only in the near UV, special filters may be used. For UV with wavelengths shorter than 350 nm, usually special quartz lens systems must be used, which do not absorb the radiation.

Digital cameras use sensors that are usually sensitive to UV, but some have internal filters that block it, in order to present images in truer color as they would be seen by the eye. Some of these systems may be adapted by removing the internal UV filter, and adding an external visible light filter. Others have no internal filter and can be used unmodified for near-UV photography, with only use of an external visible light filter. A few systems are designed for use in the UV. (See ultraviolet photography).

People cannot perceive UV light directly since the [21]

### Vacuum UV

Vacuum UV or VUV (wavelengths shorter than 200 nm) is blocked by air but can propagate through a vacuum. These wavelengths are strongly absorbed by molecular oxygen in the air. Pure nitrogen (with less than about 10 ppm oxygen) is transparent to wavelengths in the range of about 150 – 200 nm. This has practical significance, since semiconductor manufacturing processes have been using wavelengths shorter than 200 nm. By working in oxygen-free gas, the equipment does not have to be built to withstand vacuum. Some other scientific instruments that operate in this spectral region, such as circular dichroism spectrometers, are also commonly nitrogen-purged.

Technology for VUV instrumentation was largely driven by solar astronomy physics for many decades, but more recently some Marchywka Effect).

### Extreme UV

Extreme UV (EUV) is characterized by a transition in the physics of interaction with matter: wavelengths longer than about 30 nm interact mainly with the chemical valence electrons of matter, whereas shorter wavelengths interact mainly with inner-shell electrons and nuclei. The long end of the EUV/XUV spectrum is set by a prominent He+ spectral line at 30.4 nm. XUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50% of XUV radiation at normal incidence. This technology, which was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, has been used to make telescopes for solar imaging (current examples are SOHO/EIT and TRACE), and equipment for nanolithography (printing of very small-scale traces and devices on microchips).

## Human health-related effects of UV radiation

The health effects ultraviolet radiation has on fluorescent lamps and health.

### Beneficial effects

#### Vitamin D

UVB exposure induces the production of vitamin D in the skin at a rate of up to 1,000 IUs per minute. The majority of positive health effects are related to this vitamin. It has regulatory roles in calcium metabolism (which is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density), immunity, cell proliferation, insulin secretion, and blood pressure.[22]

#### Aesthetics

Too little UVB radiation may lead to a lack of vitamin D. Too much UVB radiation may lead to skin color) leads to a limited amount of direct DNA damage. This is recognized and repaired by the body, then melanin production is increased, which leads to a long-lasting tan. This tan occurs with a 2-day lag phase after irradiation.

#### Medical applications

Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as [24]

### Harmful effects

An overexposure to UVB radiation can cause [27]

UVC rays are the highest energy, most dangerous type of ultraviolet light.

On 13 April 2011 the International Agency for Research on Cancer of the World Health Organization classified all categories and wavelengths of ultraviolet radiation as a Group 1 carcinogen. This is the highest level designation for carcinogens and means “There is enough evidence to conclude that it can cause cancer in humans”.

Ultraviolet photons harm the thymine dimer” makes a bulge, and the distorted DNA molecule does not function properly.

#### Skin

##### Cancer risk
 “ Ultraviolet (UV) irradiation present in sunlight is an environmental human immunosuppression. ” — Matsumura and Ananthaswamy , (2004)[28]

UVA, UVB, and UVC can all damage [31]

Because UVA does not cause reddening of the skin (erythema), it is not measured in the usual types of [33]

The reddening of the skin due to the action of sunlight depends both on the amount of sunlight and on the sensitivity of the skin (“erythemal action spectrum”) over the UV spectrum.

UVB light can cause direct DNA damage. As noted above UVB radiation ozone depletion and the ozone hole.

As a defense against UV radiation, the type and amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present, and it triggers the release of the melanin from melanocytes. However, because this process does not increase the total amount of melanin, a UVA-produced tan is largely cosmetic and does not protect against either sun burn or UVB-produced DNA damage or cancer.[34]

By contrast, UVB yields a slower tan that requires roughly two days to develop, because the mechanism of UVB tanning is to stimulate the body to produce more melanin. However, the production of melanin by UV, called [36]

##### Sunscreen safety debate

Image of a man's face with sunscreen on the left, in visible (left) and UV light, demonstrating how sunscreen protects against UV exposure. The side of the face with sunscreen is darker, showing that the sunscreen absorbs the UV light.

Medical organizations recommend patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors (see sunscreen).

However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.[42]

The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.

In an experiment by Hanson et al. published in 2006, the amount of harmful reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the amount of ROS was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high, the amount of ROS was higher in the sunscreen treated skin than in the untreated skin.[35]

Such effects can be avoided by using newer generations of filter substances or combinations that maintain their UV protective properties even after several hours of solar exposure. Sunscreen products containing photostable filters like drometrizole trisiloxane, bisoctrizole, or bemotrizinol have been available for many years throughout the world, but are not yet available in the U.S., whereas another high-quality filter, ecamsule, has also been available in the U.S. since 2006.[36]

##### Aggravation of skin diseases

Ultraviolet radiation causes aggravation of several skin conditions and diseases, including:

#### Eye

High intensities of UVB light are hazardous to the eyes, and exposure can cause pinguecula formation.

UV light is absorbed by molecules known as retina can be damaged.

Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. Given that light may reach the eye from the sides, full coverage eye protection is usually warranted if there is an increased risk of exposure, as in high altitude mountaineering. Mountaineers are exposed to higher than ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice.

Ordinary, untreated polycarbonate, inherently block most UV. There are protective treatments available for eyeglass lenses that need it, which will give better protection. But even a treatment that completely blocks UV will not protect the eye from light that arrives around the lens.

## Degradation of polymers, pigments and dyes

UV damaged polypropylene rope (left) and new rope (right)

Many sunlight. The problem appears as discoloration or fading, cracking, and, sometimes, total product disintegration if cracking has proceeded sufficiently. The rate of attack increases with exposure time and sunlight intensity.

It is known as UV degradation, and is one form of polymer degradation. Sensitive polymers include thermoplastics, such as polypropylene, polyethylene, and poly(methyl methacrylate) as well as speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. They include tertiary carbon atoms, which in polypropylene occur in every repeat unit. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength. The impact of UV on polymers is used in nanotechnology, transplantology, X-ray lithography and other fields for modification of properties (roughness, hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet (VUV).[46]

IR spectrum showing carbonyl absorption due to UV degradation of polyethylene

In addition, many watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV light. Tinted glasses, such as sunglasses also provide protection from UV rays.

## Blockers and absorbers

Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (UV degradation (photo-oxidation) of a material. A number of different UVAs with different absorption properties exist. UVAs can disappear over time, so monitoring of UVA levels in weathered materials is necessary.

In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone and octyl methoxycinnamate, are known as absorbers. They are contrasted with physical “blockers” of UV radiation such as titanium dioxide and zinc oxide. (See sunscreen for a more complete list.)

## Applications of UV

By wavelength:[47]

### Imaging

#### Astronomy

In space observatory.)

#### Fire detection

Ultraviolet detectors generally use either a solid-state device, such as one based on Earth's atmosphere. The result is that the UV detector is “solar blind”, meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.

UV detectors are sensitive to most fires, including X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.

#### Checking high voltage electrical insulation by corona discharge detection

An application of UV is to detect corona discharge (often called “corona”) on electrical apparatus. Degradation of insulation in electrical apparatus or pollution causes corona, wherein a strong electric field ionizes the air and excites nitrogen molecules, causing the emission of ultraviolet radiation. The corona degrades the insulation level of the apparatus. Corona produces ozone and to a lesser extent nitrogen oxide, which may subsequently react with water in the air to form nitrous acid and nitric acid vapour in the surrounding air.[49]

### Use of sources

#### Fluorescent lamps

mercury vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.

The main mercury emission wavelength is in the UVC range. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous.

The light from a mercury lamp is predominantly at discrete wavelengths. Other practical UV sources with more continuous emission spectra include mercury-xenon arc lamps, metal-halide arc lamps, and tungsten-halogen incandescent lamps.

#### Lasers

Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology and keratectomy), chemistry (MALDI), free air secure communications and computing (optical storage). They can be made by applying frequency conversion to lower-frequency lasers, or from Ce:LiSAF crystals (cerium doped with lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory.[18]

### Fluorescent dye related uses

#### Fluorescent optical brighteners

Colorless fluorescent dyes that emit blue light under UV are added as textile finishing agents. These ubiquitous dyes are the reason for the bright blue fluorescence of many papers and fabrics under UV. The extra blue light emitted by these agents counteracts yellow tints that may be present, and causes the colors and whites to appear whiter or (if colored) more brightly and purely colored.

UV fluorescent dyes that glow in the primary color of paints, papers and textiles, also are used to enhance the color of these materials.

#### Paints

Paints that contain dyes that glow under UV are used in a number of art and esthetic applications.

#### Security

A bird appears on many Visa credit cards when they are held under a UV light source

To help prevent Visa stamps and stickers on passports of visitors contain large detailed seals made of such inks, that are invisible under normal light, but strongly visible under UV illumination. Many passports have UV-sensitive (fluorescent) watermarks on all pages. Currencies of various countries' banknotes have an image, as well as many multicolored fibers, that are visible only under ultraviolet light.

Some brands of pepper spray will leave an invisible chemical (UV dye) that is not easily washed off on a pepper-sprayed attacker, which would help police identify them later.[50]

### Analytic uses

#### Forensics

UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood and saliva.UV-Vis microspectroscopy is also used to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.

#### Authentication

In other detective work including authentication of various collectibles and art, and detecting counterfeit currency even absent of UV-fluorescent marker dyes (for use of such dyes, see “security” section above). Even unmarked materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short-wave ultraviolet versus long-wave ultraviolet.

#### Reading otherwise illegible papyri and manuscripts

Using multi-spectral imaging it is possible to read illegible papyrus, such as the burned papyri of the Villa of the Papyri or of Oxyrhynchus, or the Archimedes palimpsest. The technique involves taking pictures of the illegible document using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion can be found for distinguishing ink from paper on the papyrus surface. Simple NUV sources can be used to highlight faded iron-based ink on vellum.[53]

#### Chemical markers

UV fluorescent genetics as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of use and interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.

#### Sanitary compliance

Ultraviolet light aid in the detection of organic mineral deposits that remain on surfaces where periodic cleaning and sanitizing may not be properly accomplished. Both urine and phosphate soaps are easily detected using UV inspection. Pet urine deposits in carpeting or other hard surfaces can be detected for accurate treatment and removal of mineral tracers and the odor-causing bacteria that feed on proteins within. Many hospitality industries use UV lamps to inspect for unsanitary bedding to determine lifecycle for mattress restoration as well as general performance of the cleaning staff.[citation needed] A perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.

#### Analyzing minerals

A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.

Ultraviolet lamps are also used in analyzing fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet.

### Material science uses

#### Photolithography

Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The light causes chemical reactions to occur in the photoresist, and, after development (a step that removes either the exposed or the unexposed photoresist), a pattern determined by the mask remains on the sample. Steps may then be taken to “etch” away, deposit on or otherwise modify areas of the sample where no photoresist remains.

UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components,[54] and printed circuit boards.

Photolithography processes (Processes used to fabricate electronic integrated circuits) especially make use of Extreme Ultraviolet radiations. For example, the microprocessor manufacturing processes implemented by major companies such as Intel, AMD, Qualcomm make use of EUV light pencil to draw elecronic circuits on silicon wafers at subatomic scales. Latest microprocessor devices manufactured in this way have their onchip integrated circuitry of 22 nm size (latest process technology by Intel as of 2012). Other integrated chip manufacturing processes help fabricate electronic chips of standard sizes of 32 nm, 45 nm, 65 nm. Going forward the thickness of electronic circuits on these chips would further come down to 14 nm and then to thickness range of 7 nm, 5 nm and 4 nm. Reducing the thickness of circuits on silicon wafer chips provide advantages of low power usage, lesser heating and faster response time along with providing faster circuitry on smaller form factors (miniaturization). All this becomes possible using EUV-based photolithographic processes.

#### Curing of electronic potting resins

Electronic components that require clear transparency for light to exit or enter (photo voltaic panels and sensors) can be potted using acrylic resins that are cured using UV light energy. The advantages are low VOC emissions and rapid curing.

#### Curing of inks, adhesives, varnishes and coatings

Certain inks, coatings, and printing, and dental fillings. Curing of decorative finger nail “gels”.

An industry has developed around the manufacture of UV sources for UV curing applications. This includes Fe (iron, doped)-based bulbs are used, which can be energized with electric arc or microwaves. Lower-power sources (fluorescent lamps, LED) can be used for static applications, and, in some cases, small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.

#### Erasing EPROM modules

Some flash memory chips in most devices.

#### Preparing low surface energy polymers

UV radiation is useful in preparing low surface energy surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger.

#### UV solar cells and UV degradation of solar cells

Japan's National Institute of Advanced Industrial Science and Technology (AIST) has succeeded in developing a transparent solar cell that uses ultraviolet light to generate electricity but allows visible light to pass through it. Most conventional solar cells use visible and infrared light to generate electricity. In contrast, the innovative new solar cell uses ultraviolet radiation. Used to replace conventional window glass, the installation surface area could be large, leading to potential uses that take advantage of the combined functions of power generation, lighting and temperature control.[55]

Also PEDOT-PSS solar cells is an ultraviolet (UV) light-selective and -sensitive photovoltaic cell easily fabricated.[56]

On the other hand, a nanocrystalline layer of Cu2O in the construction of photovoltaic cells increases their ability to utilize UV radiations for photocurrent generation.[57]

#### Nondestructive testing

UV light of a specified spectrum and intensity is used to stimulate fluorescent dyes so as to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (magnetic particle inspection).

#### Postage stamps

Postage stamps are tagged with a phosphor which glows under UV light (the U.S. uses short wave UV) to permit automatic detection of the stamp and facing of the letter.

### Biology related uses

#### Air purification

Using a spores into harmless inert byproducts. The cleansing mechanism of UV is a photochemical process. The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. These compounds break down when exposed to high-intensity UV at 240 to 280 nm. Short-wave ultraviolet light can destroy DNA in living microorganisms and break down organic material found in indoor air. UVC's effectiveness is directly related to intensity and exposure time.

UV light has also been shown (by KJ Scott et al) as effective in reducing gaseous contaminants such as iron oxides remove the ozone produced by the UV lamp.

#### Microbial sterilization

A low pressure mercury vapor discharge tube floods the inside of a sterilizing microbiological contaminants from irradiated surfaces.

Ultraviolet lamps are used to dimerize; if enough of these defects accumulate on a microorganism's DNA, its replication is inhibited, thereby rendering it harmless (even though the organism may not be killed outright). However, since microorganisms can be shielded from ultraviolet light in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.

#### Disinfecting drinking water

UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection is the process of using PET bottles and sunlight to disinfect water. Ultraviolet germicidal irradiation is the generic process to inactivate microorganisms in water, air, medical environments etc.

New York City has approved the construction of a 2.2 billion US gallon per day (535,000 m3/hr) ultraviolet drinking water disinfection facility due to be online in 2012.[63]

It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens that have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. The findings resulted in the use of UV radiation as a viable method to treat drinking water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation.[64] It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.

Solar water disinfection[65] (SODIS) has been extensively researched in Switzerland and has proven ideal to treat small quantities of water cheaply using natural sunlight. Contaminated water is poured into transparent plastic bottles and exposed to full sunlight for six hours. The sunlight treats the contaminated water through two synergetic mechanisms: UV-A irradiation and increased water temperature. If the water temperatures rises above 50 °C (120 °F), the disinfection process is three times faster.

#### Food processing

As consumer demand for fresh and “fresh-like” food products increases, the demand for nonthermal methods of food processing is likewise on the rise. In addition, public awareness regarding the dangers of food poisoning is also raising demand for improved food processing methods. Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV light can be used to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet light source.[66] The effectiveness of such a process depends on the UV absorbance of the juice (see Beer's law).

#### Biological surveys and pest control

Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet light. Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on a yellow to green color under UV illumination, thus assisting in the control of these arachnids. Many birds have patterns in their plumage that are invisible at usual wavelengths but observable in ultraviolet, and the urine and other secretions of some animals, including dogs, cats, and human beings, is much easier to spot with ultraviolet. Urine trails of rodents can be detected by pest control technicians for proper treatment of infested dwellings.

Butterflies use ultraviolet as a communication system for sex recognition and mating behavior.

Many insects use the ultraviolet wavelength emissions from celestial objects as references for flight navigation. A local ultraviolet emitter will normally disrupt the navigation process and will eventually attract the flying insect.

Entomologist using a UV light for collecting Chaco.

Ultraviolet traps called faunistic survey studies.

#### Photochemotherapy

Exposure to UVA light while the skin is hyper-photosensitive by taking PUVA may be used only a limited number of times over a patient's lifetime.

#### Phototherapy

Exposure to UVB light, in particular, the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like [68]

Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and repeated sessions may be required before results are noticeable. Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. Home UVB systems are common solutions for those whose conditions respond to treatment. Home systems permit patients to treat themselves every other day (the ideal treatment regimen for most) without the frequent, costly trips to the office/clinic and back.

Side-effects may include itching and redness of the skin due to UVB exposure, and possibly sunburn, if patients do not minimize exposure to natural UV rays during treatment days. Cataracts can frequently develop if the eyes are not protected from UVB light exposure. To date, there is no link between an increase in a patient's risk of skin cancer and the proper use of narrow-band UVB phototherapy.[70] “Proper use” is generally defined as reaching the “Sub-Erythemic Dose” (S.E.D.), the maximum amount of UVB your skin can receive without burning. Certain fungal growths under the toenail can be treated using a specific wavelength of UV delivered from a high-power LED (light-emitting diode) and can be safer than traditional systemic drugs.

Note that this is different from phototherapy for physiological neonatal jaundice in infants, which uses blue light, not UV.

#### Herpetology

Reptiles need long wave UV light for de novo synthesis of vitamin D. Vitamin D is needed to metabolize calcium for bone and egg production. Thus, in a typical reptile enclosure, a fluorescent UV lamp should be available for vitamin D synthesis. This should be combined with the provision of heat for basking, either in the same or by another lamp.

[75]

## Evolutionary significance

Evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet light. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy (see picture above). This leads to frameshifting during genetic replication and protein synthesis, usually killing the organism. As early prokaryotes began to approach the surface of the ancient oceans, before the protective ozone layer had formed, blocking out most wavelengths of UV light, they almost invariably died out. The few that survived had developed enzymes that verified the genetic material and broke up thymine dimer bonds, known as base excision repair enzymes. Many enzymes and proteins involved in modern mitosis and meiosis are similar to excision repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome UV light.[76]

## References

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2. ^ “Reference Solar Spectral Irradiance: Air Mass 1.5”. Retrieved 2009-11-12.
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5. ^ The ozone layer protects humans from this. Lyman, T. (1914). “Victor Schumann”. Astrophysical Journal 38: 1–4. Bibcode 1914ApJ….39….1L. doi:10.1086/142050.
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8. ^ Solar constant at ground level
9. ^ “Reference Solar Spectral Irradiance: Air Mass 1.5”. Retrieved 2009-11-12.
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15. ^ insect
16. ^ Klose, Jules Z.; Bridges, J. Mervin; Ott, William R. (June 1987). “NBS Measurement Services: Radiometric Standards in the VUV” (PDF). NBS Special publication (US Dept. of Commerce) (250-3).
17. ^ [1] UV laser diode, not module with DPSS technology.
18. . Retrieved 2008-01-11.
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20. ^ M A Mainster (2006). “Violet and blue light blocking intraocular lenses: photoprotection versus photoreception”. British Journal of Ophthalmology 90 (6): 784–792.
21. ^ David Hambling (29 May 2002). “Let the light shine in”. The Guardian.
22. ^ “Oregon State University”. Lpi.oregonstate.edu. Retrieved 2011-11-08.
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27. ^ C.Michael Hogan. 2011. Sunlight. eds. P.saundry & C.Cleveland. Encyclopedia of Earth.
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34. ^ https://www.ncbi.nlm.nih.gov/pubmed/20979596 Pigment Cell Melanoma Res. 2011 Feb;24(1):136-47. doi: 10.1111/j.1755-148X.2010.00764.x. Epub 2010 Oct 06. The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin. Miyamura Y, et al. PMID 20979596
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42. ^ European Guidelines for Photodermatoses > 2 Photoaggravated Disorders at European Dermatology Forum
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51. ^ Anja Fiedler, Mark Benecke et al.. “Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source”. Retrieved 2009-12-10.
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68. ^ Hearn, R.M.R.; Kerr, A.C.; Rahim, J.; Ferguson, R.S.; Dawe, R.S. (2008). “Incidence of skin cancers in 3867 patients treated with narrow-band ultraviolet B phototherapy.”. British Journal of Dermatology (159): 931–5. doi:10.1111/j.1365-2133.2008.08776.x.
69. ^ Black, R.J.; Gavin, A.T. (2005). “Photocarcinogenic risk of narrowband ultraviolet B (TL-01) phototherapy: early follow-up data.”. British Journal of Dermatology (154): 551–7. doi:10.1111/j.1365-2133.2005.06537.x.
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# UVA

UVA or Uva may refer to:

## UVA

Colleges and universities

## Uva

• Uva, Latin for Uvea, pigmented layer of the eye lying beneath the outer layer
Places
People

# tanning booth

A tanning booth is a device that emits tanning bed, but the design is such that it is intended to be used while standing up, rather than lying down.

Tanning booth.

Tanning booths generally use 160 watt VHO (Very High Output) or 180 watt VHO-R (Very High Output with Reflector) lamps which is similar to the Mediterranean sun during mid day. Some less expensive systems use standard 100 watt HO (High Output) or RUVA (Reflector UVA) lamps. Many people confuse “VHO-R” and “VHR “, with the latter being a trademark of Cosmedico lamps for their versions of the VHO-R lamps.[1] The average tanning booth has from 32 to 56 lamps and uses a 10 to 15 minute tanning session time.

## Comparing to tanning beds

Tanning booths are similar but distinct from tanning beds in that they are vertical rather than horizontal, but there are generally other differences as well. Most tanning booths use the higher watt VHO and VHO-R lamp, which consume 160 and 180 watts respectively, while most tanning beds use 100W HO lamps, although there are many exceptions. Tanning booths are often said to give the user a better tan because it is easier to move while tanning, and most have handles above the head, which makes tanning under the arms and on the sides easier. Most booths do not have a reflector system behind the lamps because they use the VHO-R lamps, which have a more effective reflector built inside the lamp itself. This forces all the light to be focused out the front of the lamp, reducing lost UV from phase cancellation. This is where two opposing waves (in this case, UV) that are out of phase with each other partially cancelling each other out, resulting in a loss of net UV that reaches the user.

Another difference that is not as obvious is that there are no pressure points when tanning inside a booth. A person using a tanning bed is supported by the acrylic, and in these areas the blood flow is reduced. Melanin production is somewhat reduced in these areas leading to a tan that is not completely even. For most individuals, this isn't very obvious but certain individuals will experience circular areas with slight but noticeably less tan in those pressure areas. Most (but not all) tanning booths do not have acrylics and instead use a wire mesh to protect the user from the lamps. Although this results in a somewhat higher UV transmission, it does not offer the same protection that a solid acrylic sheet offers.

It is very common for tanning booths to have shorter exposure times than tanning beds. This is partially due to the more common use of the 160-180 watt lamps, which produce more UVB than a 100w lamp. Another factor is the choice of most manufacturers to use a higher UVB style lamp. Because the FDA regulates exposure time using a method that biases against UVB (for all tanning units), this reduces the average exposure time from the traditional 15 to 20 minutes found on most tanning beds, to 10 to 15 minutes, with some booths even lower. Tanning booths are subject to the same regulations as tanning beds, including posting the suggested time exposure in a conspicuous place on the tanning unit, and in the original owners manual.

## Common use

Tanning booths are not as common as tanning beds because they generally cost significantly more and because they are not as comfortable, as you tan standing up. This limits the adoption of tanning booths over tanning bed particularly in the residential market, where comfort and price are primary considerations for purchasing. There are no published statistics on the number of booths sold versus tanning beds, as all US tanning bed manufacturers are privately held companies and these numbers are considered proprietary. Anecdotal evidence would indicate that less than 10% of the tanning units in professional tanning salons are booths.

One reason professional salons may choose a booth over a bed is the amount of space required, as a booth requires significantly less square footage than a bed. Also, many booths have the option of a dressing room attached to the unit, which means the salon owner doesn't have to build a special room to house the unit, reducing their initial cost to install. This often offsets the higher cost of the unit.

## Risks

As with any device that emits sun tanning for a more complete list of the potential hazards associated with tanning indoors or out.

UV Tanning substantially raise risks of skin cancer, including melanoma.[2]

Overexposure to ultraviolet radiation is known to cause [7]

The US Public Health Service states that UV radiation, including the use of sun lamps and sun beds are “known to be a human carcinogen.”[3] It further states that the risk of developing cancer in the years after exposure is greatest in people under 30 years old.

## Regulation

Regulation of tanning using ultra-violet lamps has increased, particularly for people under 30 years of age, due to the greatly increased risk of skin cancers.[10] have banned the use of tanning booths and beds by those under eighteen.

Proposed laws in some areas totally ban them. In February 2012 the state Government of New South Wales in Australia announced its intention to ban solariums (including tanning beds), starting in 2014.[11]

## References

1. ^ http://tess2.uspto.gov/bin/showfield?f=doc&state=4008:mhm30q.2.10
2. ^ CNN. 27 May 2010.
3. . Retrieved 2009-07-29.
4. http://www.nejm.org/doi/abs/10.1056/NEJM199711133372003.
5. http://pubs.rsc.org/en/Content/ArticleHTML/2002/PP/B201230H.
6. http://archderm.ama-assn.org/cgi/reprint/127/1/99.pdf.
7. ^ 10.1542/peds.2007-2256. Retrieved February 4, 2012
8. ^ Rebecca Smith(April 8, 2010) “Children banned from using sunbeds” The Telegraph. Retrieved 8 April 2010.
9. ^ Bell, Kyle W. (October 13, 2011). “California Bans Tanning Bed Use for Minors”. Gather News. Retrieved February 4, 2012.
10. ^ Standards Australia/Standards New Zealand. Australian/New Zealand Standard AS/NZS 2635 (Solaria for cosmetic purposes): Standards Australia/Standards New Zealand, 2008.
11. ^ “Solariums banned across NSW”. ABC News (Australia). 4 February 2012. Retrieved 4 February 2012.

## 

Tanning addiction is a rare syndrome where an individual appears to have a physical or psychological addiction to sunbathing or the use of tanning beds.[1] The mechanism of the addiction is unknown at this time.

## Medical evidence

In 2005, a group of dermatologists published a study showing that frequent tanners experience a loss of control over their tanning schedule, displaying a pattern of addiction similar to smokers and alcoholics. [2]

Biochemical evidence indicates that tanning addicts are addicted to an opioid release experienced during tanning. When frequent tanners took an endorphin blocker in a 2006 study, they experienced severe withdrawal symptoms, while infrequent tanners experienced no withdrawal symptoms under the same conditions. [3]

## Tanorexia

Tanorexia is the term often used to describe a condition in which a person participates in excessive outdoor skin complexion because they perceive themselves as unacceptably pale. The syndrome is different than tanning addiction, although both may fit into the same syndrome and can be considered a subset of tanning addiction.

Although the term “tanorexia” has been commonly used by the media and several doctors to describe the syndrome, both the word and syndrome have not been widely accepted by the medical community, and is considered slang by many. The term was coined after the medical condition alcoholic) to the end of any action or food someone enjoys extensively and often (e.g., “choc-aholic,” “work-aholic” “golf-aholic,” “shop-aholic,” etc.).

Serious cases of tanorexia can be considered dangerous because many of the more popular methods of tanning (such as those mentioned above) require prolonged exposure to skin cancer.

Extreme instances may be an indication of body dysmorphic disorder (BDD), [4] a mental disorder in which one is extremely critical of his or her physique or self-image to an obsessive and compulsive degree. As it is with anorexia, a person with BDD is said to show signs of a characteristic called distorted body image. In layman's terms, anorexia sufferers commonly believe they are overweight, many times claiming they see themselves as “fat”, when in reality, they are nutritionally underweight and physically much thinner than the average person. In the same way, a sufferer of “tanorexia” may believe him or herself to have a much lighter – even a pale – complexion when he or she is actually quite dark-skinned.

Neither tanning addiction nor tanorexia are covered under the latest edition of the Diagnostic and Statistical Manual of Mental Disorders. However, a 2005 article in The Archives of Dermatology presents a case for UV light tanning addiction to be viewed as a type of substance abuse disorder. [2]

## Symptoms

Although the syndrome has not been officially described by the medical community, it may include the following reported symptoms: intense anxiety if a session of tanning is missed, competition among peers to see which can get the darkest tan, and chronic frustration about the color of one's skin, with the affected person being convinced his or her complexion is constantly lighter than it actually is.

## References

1. ^ Medical News Today, Tanning addiction exists, study. August 16, 2005, accessed December 30, 2007.
2. ^ b M. Warthan, T. Uchida, R. Wagner, Jr. UV Light Tanning as a Type of Substance-Related Disorder. Archives of Dermatology, August 2005; vol 141: pp 963-966.
3. ^ M. Kaur, A. Liguori, W. Lang, S. Rapp, A. Fleischer, Jr., S. Feldman. Induction of withdrawal-like symptoms in a small randomized, controlled trial of opioid blockade in frequent tanners. Journal of the American Academy of Dermatology, 54(4): p. 709-711, 2006

# Sunscreen

Sunscreen (also commonly known as sunblock, sun tan lotion, sun screen, sunburn cream or block out)[1] is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun‘s ultraviolet (UV) radiation on the skin exposed to sunlight and thus helps protect against sunburn. Skin-lightening products have sunscreen to protect lightened skin because light skin is more susceptible to sun damage than darker skin. A number of sunscreens have tanning powder to help the skin to darken or tan; however, tanning powder does not provide protection from UV rays.

Sunscreens contain one or more of the following ingredients:

• Organic chemical compounds that absorb ultraviolet light.
• Inorganic zinc oxide, or a combination of both).
• Organic particulates that mostly absorb light like organic chemical compounds, but contain multiple Tinosorb M. Since the UV-attenuating efficacy depends strongly on particle size, the material is micronised to particle sizes below 200 nm. The mode of action of this photostable filter system is governed to about 90% by absorption and 10% by scattering of UV light.

Depending on the mode of action sunscreens can be classified into physical sunscreens (i.e., those that reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light).[2]

Medical organizations such as the [4] The use of broad-spectrum (UVA/UVB) sunscreens can address this concern.

Although sunscreen is sometimes called “suntan lotion”, the latter is different in that it is used to intensify UV rays whereas the former is used to block UV rays.

### History

The first effective sunscreen may have been developed by chemist Franz Greiter in 1946. The product, called Gletscher Crème (Glacier Cream), subsequently became the basis for the company Piz Buin (named in honor of the place Greiter allegedly obtained the sunburn that inspired his concoction), which is still today a marketer of sunscreen products.[5] It has been estimated that Gletscher Crème had a sun protection factor of 2.

The first widely used sunscreen was produced by Benjamin Green, an airman and later a Bain de Soleil branding in the early 1950s.

Franz Greiter is credited with introducing the concept of sun protection factor (SPF) in 1962, which has become a worldwide standard for measuring the effectiveness of sunscreen when applied at an even rate of 2 milligrams per square centimeter (mg/cm2). Some controversy exists over the usefulness of SPF measurements, especially whether the 2 mg/cm2 application rate is an accurate reflection of people’s actual use.

Newer sunscreens have been developed with the ability to better withstand contact with sweat.

## Measurements of sunscreen protection

Sunscreen helps prevent sunburn, such as this, which has blistered

### Sun protection factor (SPF) and labeling requirements

Two photographs showing the effect of applying sunscreen in visible light and in UVA. The photograph on the right was taken using ultraviolet photography shortly after application of sunscreen to half of the face.

The sun protection factor of a sunscreen is a laboratory measure of the effectiveness of sunscreen — the higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that causes sunburn).[2]

The SPF is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, as a multiple of the amount required without the sunscreen.[6] There is a popular oversimplification of how SPF determines how long one can stay in the sun. For example, many users believe that, if they normally get sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun fifteen hours (i.e. fifteen times longer) without getting sunburn. This would be true if the intensity of UV radiation were the same for the whole fifteen hours as in the one hour, but this is not normally the case. Intensity of solar radiation varies considerably with time of day. During early morning and late afternoon, the sun's radiation intensity is highly diminished since it must pass through more of the Earth's atmosphere while it is near the horizon.

In practice, the protection from a particular sunscreen depends, besides on SPF, on factors such as:

• The skin type of the user.
• The amount applied and frequency of re-application.
• Activities in which one engages (for example, swimming leads to a loss of sunscreen from the skin).
• Amount of sunscreen the skin has absorbed.

The SPF is an imperfect measure of skin damage because invisible damage and skin aging are also caused by [12]

Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. In the [16]

Others have proposed restricting the active ingredients to an SPF of no more than 50, due to lack of evidence that higher dosages provide more meaningful protection (especially due to the logarithmic nature of the scale).[17]

UV-B sunlight spectrum (on a summer day in the Netherlands), along with the CIE Erythemal action spectrum. The effective spectrum is the product of the former two.

The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an [19]

Mathematically, the SPF is calculated from measured data as

$mathrm{SPF} = frac{int A(lambda) E(lambda)dlambda}{int A(lambda) E(lambda)/mathrm{MPF}(lambda) , dlambda},$

where $E(lambda)$ is the solar irradiance spectrum, $A(lambda)$ the erythemal action spectrum, and $mathrm{MPF}(lambda)$ the monochromatic protection factor, all functions of the wavelength $lambda$. The MPF is roughly the inverse of the transmittance at a given wavelength.

The above means that the SPF is not simply the inverse of the transmittance in the UV-B region. If that were true, then applying two layers of SPF 5 sunscreen would be equivalent to SPF 25 (5 times 5). The actual combined SPF is always lower than the square of the single-layer SPF.

### Measurements of UVA protection

#### Persistent pigment darkening (PPD)

The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring UVB light protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oréal.

Instead of measuring erythema or reddening of the skin, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an in vivo test like SPF. In addition, Colipa has introduced a method that, it is claimed, can measure this in vitro and provide parity with the PPD method.[20]

### SPF equivalence

The UVA seal used in the EU

As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF. This should be a UVA PF of at least 1/3 of the SPF to carry the UVA seal. The implementation of this seal is in its phase-in period,[[21]

A set of final U.S. FDA rules effective from summer 2012 defines the phrase “broad spectrum” as having a UVA SPF at least as high as the UVB SPF.[16]

#### Star rating system

In the UK and Ireland, the [17]

#### PA system

Asian brands, particularly Japanese ones, tend to use The Protection Grade of UVA (PA) system to measure the UVA protection a sunscreen provides.

The Protection Grade of UVA (PA) system is based on the PPD reaction and is now widely adopted on the labels of sunscreens. According to the Japan Cosmetic Industry Association PA+ corresponds to a UVA protection factor between two and four, PA++ between four and eight, and PA+++ more than eight.

## Sunblock is a type of sunscreen

A tube of SPF 15 sun block lotion

Sunblock typically refers to opaque sunscreen that is effective at blocking both UVA and UVB rays and uses a heavy carrier oil to resist being washed off. zinc oxide are two of the important ingredients in sunblock. Unlike the organic sun-blocking agents used in many sunscreens, these metal oxides do not degrade with exposure to sunlight.

The use of the word “sunblock” in the marketing of sunscreens is controversial. The FDA has considered banning such use because it can lead consumers to overestimate the effectiveness of products so labeled.[23]

For total protection against damage from the sun, the skin needs to be protected from UVA, UVB and IRA (infrared light). Roughly 35% of solar energy is IRA.[24]

## Potential health risks

As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB on the other hand yields a tan that takes roughly two days to develop because it stimulates the body to produce more melanin. The photochemical properties of melanin make it an excellent photoprotectant.

Sunscreen chemicals, on the other hand, cannot dissipate the energy of the excited state as efficiently as melanin and therefore the penetration of sunscreen ingredients into the lower layers of the skin increases the amount of free radicals and reactive oxygen species (ROS).[25]

Some sunscreen lotions now include compounds such as Phlebodium aureum.

Some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.stratum corneum may be large enough to cause damage. In one study of sunscreens, the authors write:

The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.[29]

In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen species was measured in untreated and in sunscreen-treated skin. In the first 20 minutes the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin.[25] The authors emphasize that if enough sunscreen remains in the surface this effect would be eliminated, enhancing the message that sunscreen needs to be applied and reapplied sufficiently and correctly for it to work.

George Zachariadis and E Sahanidou of the Laboratory of Analytical Chemistry, at Aristotle University, in Thessaloniki, Greece, have now carried out an ICP-AES analysis of several commercially available sunscreen creams and lotions. “The objective was the simultaneous determination of titanium and several minor, trace or toxic elements (aluminum, zinc, magnesium, iron, manganese, copper, chromium, lead, and bismuth) in the final products,” the researchers say. They concluded that “Most of the commercial preparations that were studied showed generally good agreement to the ingredients listed on the product label.” However, they also point out that the quantitative composition of the products tested cannot be assessed because the product labels usually do not provide a detailed break down of all ingredients and their concentrations. They also point out that, worryingly, their tests consistently revealed the presence of elements not cited in the product formulation, which emphasized the need for a standardized and official testing method for multi-element quality control of these products.[30]

Some epidemiological studies indicate an increased risk of [40]

Adverse health effects may be associated with some synthetic compounds in sunscreens.[42]

Concerns have been raised regarding the use of nanoparticles in sunscreen.[44] In 2006 the Therapeutic Goods Administration of Australia concluded a study and found:

“There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these cells (photo-mutagenicity with zinc oxide). However, this would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer (stratum corneum) of the skin.” [43]

### Vitamin D

Artificial sunscreen absorbs ultraviolet light and prevents it from reaching the skin. It has been reported that sunscreen with a sun protection factor (SPF) of 8 based on the UVB spectrum can decrease vitamin D synthetic capacity by 95 percent, whereas sunscreen with an SPF of 15 can reduce synthetic capacity by 98 percent (Matsuoka et al., 1987).[45]

This was leading to deficiency in Australia after a government campaign to increase sunscreen use.[48]

## Active ingredients

The principal ingredients in sunscreens are usually [53] and various other photostabilisers.

### FDA allowable ingredients

The following are the FDA allowable active ingredients in sunscreens:

UV-filter Other names Maximum concentration Permitted in these countries Results of safety testing
p-Aminobenzoic acid PABA 15% (EC- banned from sale to consumers from 8 October 2009) USA, AUS Protects against skin tumors in mice.[56] Shown to increase DNA defects, however, and is now less commonly used.
Padimate O OD-PABA, octyldimethyl-PABA, σ-PABA 8% (EC,USA,AUS) 10% (JP)

(Not currently supported in EU and may be delisted)

EC, USA, AUS, JP Not tested
Phenylbenzimidazole sulfonic acid Ensulizole, Eusolex 232, PBSA, Parsol HS 4% (US,AUS) 8% (EC) 3% (JP) EC,USA, AUS, JP Genotoxic in bacteria[57]
Cinoxate 2-Ethoxyethyl p-methoxycinnamate 3% (US) 6% (AUS) USA, AUS Not tested
Dioxybenzone Benzophenone-8 3% USA, AUS Not tested
Oxybenzone Benzophenone-3, Eusolex 4360, Escalol 567 6% (US) 10% (AUS,EU) 5% (JP) EC, USA, AUS, JP Not tested
Homosalate Homomethyl salicylate, HMS 10% (EC, JP) 15% (US,AUS) EC, USA, AUS, JP Not tested
Menthyl anthranilate Meradimate 5% USA, AUS Not tested
Octocrylene Eusolex OCR, 2-Cyano-3,3-diphenyl acrylic acid, 2-ethylhexylester 10% EC,USA, AUS, JP Increases ROS[25]
Octyl methoxycinnamate Octinoxate, EMC, OMC, Ethylhexyl methoxycinnamate, Escalol 557, 2-Ethylhexyl-paramethoxycinnamate, Parsol MCX 7.5% (US) 10% (EC,AUS)20% (JP) EC,USA, AUS, JP
Octyl salicylate Octisalate, 2-Ethylhexyl salicylate, Escalol 587, 5% (EC,USA,AUS) 10% (JP) EC,USA, AUS, JP Not tested
Sulisobenzone 2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid, 3-Benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, Benzophenone-4, Escalol 577 5% (EC) 10% (US, AUS, JP) EC,USA, AUS, JP
Trolamine salicylate Triethanolamine salicylate 12% USA, AUS Not tested
Avobenzone 1-(4-methoxyphenyl)-3-(4-tert-butyl
phenyl)propane-1,3-dione, Butyl methoxy dibenzoylmethane, BMDBM, Parsol 1789, Eusolex 9020
3% (US) 5% (EC,AUS)10% (JP) EC, USA, AUS, JP Not available[58]
Ecamsule Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid 10% EC,AUS (US:Approved in certain formulations up to 3% via New Drug Application (NDA) Route) Protects against skin tumors in mice[61]
Titanium dioxide CI77891 25% (No limit Japan) EC,USA, AUS, JP Not tested
Zinc oxide 25% (US) 20% (AUS)

(EC-25% provided particle size >100 nm) (Japan, No Limit)

EC,USA, AUS, JP Protects against skin tumors in mice[59]

Other ingredients approved within the EU[63] that have not been included in the current FDA Monograph:

UV-filter Other names Maximum concentration Permitted in
4-Methylbenzylidene camphor Enzacamene, Parsol 5000, Eusolex 6300, MBC 4%* EC, AUS
Tinosorb M Bisoctrizole, Methylene Bis-Benzotriazolyl Tetramethylbutylphenol, MBBT 10%* EC, AUS, JP
Tinosorb S Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine 10% (EC, AUS) 3% (JP)* EC, AUS, JP
Neo Heliopan AP Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT 10% EC, AUS
Mexoryl XL Drometrizole Trisiloxane 15% EC, AUS
Benzophenone-9 Uvinul DS 49, CAS 3121-60-6, Sodium Dihydroxy Dimethoxy Disulfobenzophenone [64] 10% JP
Uvinul T 150 Octyl triazone, ethylhexyl triazone, EHT 5% (EC, AUS) 3% (JP)* EC, AUS
Uvinul A Plus Diethylamino Hydroxybenzoyl Hexyl Benzoate 10% (EC,JP) EC, JP
Uvasorb HEB Iscotrizinol, Diethylhexyl butamido triazone, DBT 10% (EC) 5% (JP) * EC, JP
Parsol SLX Dimethico-diethylbenzalmalonate, Polysilicone-15 10% EC, AUS, JP
Isopentenyl-4-methoxycinnamate Isoamyl p-Methoxycinnamate, IMC, Neo Heliopan E1000, Amiloxate 10% * EC, AUS

Many of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.[65]

* Time and Extent Application (TEA), Proposed Rule on FDA approval expected 2009

## Application

Protection of the skin through use of a beach umbrella

Excessive exposure to direct sunlight is potentially harmful. Excessive exposure can result in sunburn if a person does not wear sun protective clothing or use suitable sunscreen. Products with a higher SPF (Sun Protection Factor) level provide greater protection against ultraviolet radiation. However, in 1998, the Annual Meeting of the American Association for the Advancement of Science reported that some sunscreens advertising UVA and UVB protection do not provide adequate safety from UVA radiation and could give sun tanners a false sense of protection. A sunscreen should also be hypoallergenic and noncomedogenic so it does not cause a rash or clog the pores, which can cause acne.

For those choosing to tan, some dermatologists recommend the following preventative measures:

• Sunscreens that should block both UVA and UVB rays are called broad-spectrum sunscreens.
• Sunscreens need to be applied thickly enough to get the full SPF protection.
• Sunscreens should be applied 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after the sun exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.[66]
• Sun rays are strongest between 10 am and 4 pm.[67] Sun rays are stronger at higher elevations (mountains) and latitudes near the equator.
• Wearing a hat with a brim and anti-UV sunglasses can provide almost 100% protection against ultraviolet radiation's entering the eyes.
• Reflective surfaces like snow and water can greatly increase the amount of UV radiation to which the skin is exposed.

Recent evidence indicates that caffeine and caffeine sodium benzoate increase UVB-induced apoptosis both in topical and oral applications. In mice, UVB-induced hyperplasia was greatly reduced with administration of these substances. Although studies in humans remain untested, caffeine and caffeine sodium benzoate may be novel inhibitors of skin cancer.[68]

### Dosage

The dose used in [49] Provided one assumes an “average” adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area. Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face. Larger individuals should scale these quantities accordingly.

Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, some research has shown that the best protection is achieved by application 15–30 minutes before exposure, followed by one reapplication 15–30 minutes after the sun exposure begins. Further reapplication is only necessary after activities such as swimming, sweating, or rubbing/wiping.[69]

More recent research at the [71]

### Label regulations

Updated package labeling standards in the United States have been under development since 1978.

A set of final FDA rules effective from summer 2012 bans “waterproof” claims, instead requiring claims of 40 or 80 minutes “water-resistant” protection. It also requires a standardized “Drug Facts” label and requires specific FDA approval for “sunblock” and “instant protection” labels. Claims of protection over two hours are not allowed without specific approval.[16]

However, the compliance dates for these new sunscreen labeling requirements, published in June 2011, have been delayed by 6 months. The new implementation date for products with annual sales less than US \$25,000 is December 17, 2013 and that for all other products is December 17, 2012.[72]

Due to requests by several trade associations and the personal care industry, the FDA ultimately decided to extend the implementation period for 6 months from the original compliance date. This decision allows manufacturers adequate time for thorough testing and the full implementation of the new labeling requirements which cover:

• Use claims
• “Waterproof,” “sweatproof” or “sunblock” claims
• Water resistance claims
• Drug facts
• Maximum SPF value on sunscreen labels to “50 +”

These changes shall enable consumers to identify and select suitable sunscreen products offering protection from sunburn, early skin aging and skin cancer.[73]

## Hair care

Sunscreening agents are used in some hair care products such as shampoos, conditioners and styling agents to protect against protein degradation and color loss. Currently, Cinnamidopyltrimonium chloride and a few others are used to a much less degree. The common sunscreens used on skin are rarely used for hair products due to their texture and weight effects.

## Notes

1. ^ “Preventing melanoma”. Cancer Research UK. Retrieved 2009-09-22.
2. ^ What You Need To Know About Skin Cancer
3. ^ Terence SC Poon, Ross StC Barnetson and Gary M Halliday (2003). “Prevention of Immunosuppression by Sunscreens in Humans Is Unrelated to Protection from Erythema and Dependent on Protection from Ultraviolet A in the Face of Constant Ultraviolet B Protection”. J Invest Dermatol 121: 184-90.
4. ^ 70 years since the PIZ BUIN mountain inspired a man to invent the world's first sun protection cream
5. ^ “Sunburn Protection Factor (SPF)”. Food and Drug Administration (United States). 2009-04-30. . Retrieved 2009-09-25.
6. edit
7. edit
8. edit
9. 15140232.
10. ^ MSNBC.com : Sunscreen — protection or ‘snake oil?'
11. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=1076-0512&date=2000&volume=26&issue=4&spage=309.
12. ^ Commission Recommendation of 22 September 2006 on the efficacy of sunscreen products and the claims made relating thereto. Official Journal of the European Union. 2006-09-22. Retrieved 2009-09-25.
13. ^ “UV Resource Guide – Sunscreens”. Arpansa. 2008-12-20. Retrieved 2009-09-25.
14. ^ Questions and Answers on the 2007 Sunscreen Proposed Rule
15. . Retrieved 2012-04-10.
16. . Retrieved 2012-04-10.
17. ^ Optometrics products
18. ^ Dominique Moyal “How to measure UVA protection afforded by suncreen products” www.medscape.com/viewarticle/576849
19. ^ Colipa UVA method
21. ^ [1] Questions and Answers on the 2007 Sunscreen Proposed Rule
22. http://www.ewg.org/2010sunscreen/faqs-2010/#28
23. ^ P. Schroeder, PhD and J. Krutmann, MD What is Needed for a Sunscreen to Provide Complete Protection
24. ^ 17015167.
25. 11421064.
26. 8405372.
27. 10232823.
28. http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ArtikelNr=68291&ProduktNr=224219&Ausgabe=228903&filename=68291.pdf.
29. ^ David Bradley (August 15). “Toxic sunscreen testing”. Http://www.spectroscopynow.com/coi/cda/detail.cda?id=22103&type=Feature&chId=1&page=1 year=2009.
30. http://www.ajph.org/cgi/reprint/82/4/614.
31. 10861466.
32. 7790106.
33. 10537017.
34. ^ Vainio, H., Bianchini, F. (2000). “Cancer-preventive effects of sunscreens are uncertain”. Scandinavian Journal of Work Environment and Health 26: 529–31.
35. 9764814.
36. http://www.ncbi.nlm.nih.gov.ezproxy.its.uu.se/sites/entrez.
37. 2297503.
38. http://www.ajph.org/cgi/pmidlookup?view=long&pmid=12084704.
39. 14678916.
40. ^ Experts explore the safety of sunscreen | Straight.com
41. ^ CDC: Americans Carry Body Burden of Toxic Sunscreen Chemical | Environmental Working Group
42. . Retrieved 14 June 2009.
43. ^ Arthur Martin (12 November 2008). “Revealed: The toxic nanoparticles with asbestos-like properties found in everyday goods”. Daily Mail (London). Retrieved 14 June 2009.
44. ^ http://www.ncbi.nlm.nih.gov/books/NBK56078/
45. ^ Sexton, Reid (2007-12-09). “Slip, slop, crack: the vitamin D crisis – National”. Melbourne: theage.com.au. Retrieved 2009-09-25.
46. ^ Sexton, Reid; Hall, Louise (2007-12-09). “Be sun-smart, avoid bone D-generation risks – National”. Melbourne: theage.com.au. Retrieved 2009-09-25.
47. ^ “Dietary Supplement Fact Sheet: Vitamin D”. National Institutes of Health. Archived from the original on 2007-09-10. Retrieved 2007-09-10.
48. . Retrieved 2009-09-25.
49. ^ Neutrogena | How Helioplex Works
50. ^ Banana Boat AvoTriplex
51. 11594052.
52. ^ DSM Nutritional Products North America – Cosmetics: Basis for Performance – Parsol 340 – Octocrylene
53. 2317082.
54. 1967881.
55. 6982950.
56. 17617675.
57. 16311166.
58. ^ 17693182.
59. 14528058.
60. 8863475.
61. ^ CL1976L0768EN0150010.0001 1..107
62. ^ Australian Regulatory Guidelines for OTC Medicines – Chapter 10
63. ^
64. ^ Manage Account – Modern Medicine
65. 11712033.
67. http://www.ingentaconnect.com/content/bpl/php/2008/00000084/00000002/art00010.
68. 11712033.
69. 17493070.
70. 19614894.
71. ^
72. ^ US FDA Delays Implementation Deadlines for Sunscreen Labeling Requirements SGS SafeGuard Bulletin, Retrieved 09/27/2012

# Sunburn

Sunburn
Classification and external resources

A sunburnt back that was partially protected by a bathing suit top.
10 L55
9 692.71
MedlinePlus 003227
MeSH D013471

A sunburn is a form of suntan.

Excessive UV radiation is the leading cause of primarily non-malignant skin indirect DNA damage if the damage is not properly repaired. Proper repair occurs in the majority of DNA damage. The only cure for sunburn is slow healing, although some skin creams can help with the symptoms.

## Cause

The cause of sunburn is the direct damage that a UV-B photon can induce in DNA (left). One of the possible reactions from the excited state is the formation of a thymine-thymine cyclobutane dimer (right). This kind of damage is responsible for only 8% of all melanoma.

Sunburn is caused by UV radiation, either from the sun or from artificial sources, such as free radicals, thus indirect DNA damage.

The pain may be caused by overproduction of a protein called CXCL5, which activates nerve fibres[6].

Experiments with mice found that protection against sunburn by chemical sunscreens does not necessarily provide protection against other damaging effects of UV radiation such as enhanced melanoma growth.[7]

UV radiation sunburn and melanoma. Statistical correlation vs causal connection.

## Sunburn and skin cancer

Ultraviolet B (UVB) radiation causes dangerous sunburns and increases the risk of two types of skin cancer: [2]

Some exposure to sunlight is not only harmless but positively necessary to health. Humans need vitamin D; most is synthesised in the body by exposure of the skin to sunlight, with some from the diet. People with darker skins need more sunlight to maintain vitamin D levels. The widespread concern about over-exposure to the sun causing cancer has led some people to go too far in avoiding exposure and using sunscreen; this can lead to vitamin D deficiency and the condition of rickets due to this deficiency, particularly in children, and particularly in climates with less sunshine. Cases of rickets are, indeed, on the increase. Twenty to thirty minutes of unimpeded exposure to the sun two to three times a week are recommended.[8]

### Controversy over sunscreen

The statement sunburn causes skin cancer is considered accurate when it refers to either basal-cell carcinoma, the mildest form of cancer, or squamous cell carcinoma. However, this may be misleading when it comes to malignant melanoma (see picture: UVR sunburn melanoma)[citation needed]. The statistical correlation between sunburn and melanoma is assumed to be due to a common cause — UV radiation. Instead, this correlation may be generated via different mechanisms. Direct DNA damage is ascribed by many medical doctors to a change in behaviour of the sunscreen user due to a false sense of security afforded by the sunscreen. While some researchers believe that these confounding factors can be controlled for effectively,[9] others believe there to be insufficient correction for light-skinned individuals and indirect DNA damage.[clarification needed]

Exposure to UV rays generates [13] Whether sunscreen prevents or promotes the development of melanoma depends on the relative importance of the protective effect from the topical sunscreen versus the harmful effects of the absorbed sunscreen.

The use of sunscreen is known to prevent the direct DNA damage that causes sunburn and the two most common forms of skin cancer, basal-cell carcinoma and squamous cell carcinoma.[20]

## Other risk factors

### Location

Erythemal dose at three Northern latitudes
source: NOAA.

Because of variations in the intensity of UV radiation passing through the atmosphere, the risk of sunburn increases with proximity to the noon, when shadows are at their minimum and the sun's radiation passes more directly through the atmosphere. Regardless of one's latitude (assuming no other variables), equal shadow lengths mean equal amounts of UV radiation.

### Pharmaceutical products

Sunburn can also be caused by [22]

### Ozone depletion

In recent years, the incidence and severity of sunburn has increased worldwide, especially in the southern hemisphere, because of damage to the [25]

### Popularity of tanning

Suntans, which naturally develop in some individuals as a protective mechanism against the sun, are viewed by many in the Western world as desirable.[26] This has led to increased exposure to UV radiation from both the natural sun and solaria.

## Symptoms

Typically there is initial redness (pain, proportional in severity to both the duration and intensity of exposure.

Sunburn caused by extended exposure on a glacier.

Other symptoms are burns.

One should immediately speak to a dermatologist if one develops a skin lesion that has an asymmetrical form, has darker edges than center, changes color, or becomes larger than 1/4 inch (6 mm). (see Melanoma)

### Variations

Blisters on a shoulder caused by sunburn.

Minor sunburns typically cause nothing more than slight redness and tenderness to the affected areas. In more serious cases, blistering can occur. Extreme sunburns can be painful to the point of debilitation and may require hospital care.

### Duration

Sunburn can occur in less than 15 minutes, and in seconds when exposed to non-shielded welding arcs or other sources of intense ultraviolet light. Nevertheless, the inflicted harm is often not immediately obvious.

After the exposure, skin may turn red in as little as 30 minutes but most often takes 2 to 6 hours. Pain is usually most extreme 6 to 48 hours after exposure. The burn continues to develop for 24 to 72 hours, occasionally followed by peeling skin in 3 to 8 days. Some peeling and itching may continue for several weeks.

Long-term low-intensity exposure to sunlight is known to cause significant ageing of the skin; other health effects are not accurately known. A particular example with very noticeable ageing is that of a 69-year-old truck driver in Chicago, USA who drove in the city for 28 years. A photograph of his face[27] Window glass does not absorb UVA, which can penetrate the epidermis and upper layers of dermis. Chronic UVA exposure can cause photoageing: thickening of the epidermis and stratum corneum and destruction of elastic fibers; it can cause DNA mutations and toxicity which can lead to cancer, although less carcinogenic than UVB.

## Protection

### Skin

Sunburn peeling. The destruction of lower layers of the epidermis causes rapid loss of the top layers.

One of the most effective ways to prevent sunburn is to reduce the amount of UV radiation reaching the skin. The strength of sunlight is published in many locations as a UV index. The World Health Organization recommends to limit time in the midday sun (between 10 a.m. and 4 p.m.), to watch the UV index, to seek shade, to wear protective clothing and a wide-brim hat, and to use sunscreen.[29] Sunlight is generally strongest when the sun is close to the highest point in the sky. Due to time zones and daylight saving time, this is not necessarily at 12 p.m., but often one to two hours later.

Sunburn, photographed 2 days after a 5-hour sun exposure. The dark-red area is sunburned. The lighter-colored skin was covered by the woman's clothing during exposure.

Commercial preparations are available that block UV light, known as sunscreens or sunblocks. They have a sunburn protection factor (SPF) rating, based on the sunblock's ability to suppress sunburn: The higher the SPF rating the lower the amount of direct DNA damage.

A sunscreen rated as SPF 10 blocks 90% of the sunburn-causing UVB radiation; an SPF20-rated sunscreen blocks 95%[μl of sunscreen is applied per square cm of exposed skin. This translates into about 28 ml (1 oz) to cover the whole body of an adult male, which is much more than many people use in practice. Although UVA radiation does not cause sunburn, it does contribute to skin aging and an increased risk of skin cancer. Many sunscreens provide broad-spectrum protection, meaning that they protect against both UVA and UVB radiation.

Research has shown that the best protection is achieved by application 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.[30] This varies based on the indications and protection shown on the label — from as little as 80 minutes in water to a few hours, depending on the product selected.

When one is exposed to any artificial source of occupational UV, special protective clothing (for example, welding helmets/shields) should be worn.

There is also evidence that common foods may have some protective ability against sunburn if taken for a period before the exposure.flavonoids has also been found to have a similar effect if eaten for long periods before exposure.

### Eyes

The eyes are also sensitive to sun exposure. Wrap-around freckles, are often found within the iris.

### Diet

Dietary factors influence susceptibility to sunburn, recovery from sunburn, and risk of secondary complications from sunburn. Several dietary [38]

Sunburn increases the metabolic demands on the body, increasing the needs for water and other nutrients to prevent skin breakdown and secondary infections.[39]

## Treatment

The most important aspects of sunburn care are to avoid [41]

## Notes

1. ^ “Do sunscreens prevent skin cancer” Press release No. 132, June 5, 2000
2. ^ “Solar and ultraviolet radiation” IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 55, November 1997
3. .
4. ^ 10861466.
5. eMedicine
6. ^ J. M. Dawes, M. Calvo, J. R. Perkins, K. J. Paterson, H. Kiesewetter, C. Hobbs, T. K. Y. Kaan, C.Orengo, D. L.H. Bennett, S. B.McMahon, CXCL5 Mediates UVB Irradiation–Induced Pain. Sci. Transl. Med. 3, 90ra60 (2011). http://dx.doi.org/10.1126/scitranslmed.3002193
7. 8271307.
8. ^ guardian newspaper: Rickets warning from doctors as vitamin D deficiency widens, 22 January 2010
9. 3970815. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1976961/.
10. 15363592.
12. 17617675.
13. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0031-8655&date=2001&volume=73&issue=6&spage=600.
14. ^ Health Report – 13/09/99: Skin Cancer and Sunscreen
15. 17015167.
16. 7790106.
17. 10537017.
18. http://www.sjweh.fi/show_abstract.php?abstract_id=578.
19. 9764814.
20. http://aje.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=4025303.
21. ^ “Avoiding Sun-Related Skin Damage” – No longer available
22. ^ Sunburn-Topic Overview
23. http://www.ciesin.org/docs/001-540/001-540.html=Citation.
24. ^ Al Gore, “Earth in the Balance, Ecology and the Human Spirit”‘, 1992
25. 1616864. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1977777/.
26. ^ Healthwise Incorporated (March 27). “Suntan”. Retrieved August 26, 2006.
27. ^ Sun protection. World Health Organization.
28. 11712033.
29. 17914160.
30. 17164979.
31. 16395131.
32. 16714259. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1860212/. Retrieved 2009-09-21.
33. 14569187.
34. 01909622.
35. 0031-8655.
36. 0022-202X.
37. ^ Pullen, Richard L. et. al., “Danger! Severe sunburn in season”, Nursing Made Incredibly Easy!, July/August 2011 – Volume 9 – Issue 4 – p 13–15.
38. ^ [1]
39. ^ [2]</ref Calamine lotion can also help reduce skin irritation due to mild sunburn.

### References

• Baron ED, Fourtanier A, Compan D, Medaisko C, Cooper KD, Stevens SR (2003). “High ultraviolet A protection affords greater immune protection confirming that ultraviolet A contributes to photoimmunosuppression in humans”. J. Invest. Dermatol. 121 (4): 869–75. doi:10.1046/j.1523-1747.2003.12485.x. PMID 14632207.

Treatment for Severe Sunburns

# sun glasses

Wearing sunglasses under direct sunlight: Large lenses offer good protection, but broad temple arms are also needed against “stray light” from the sides.

Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that are colored, polarized or darkened. In the early 20th century they were also known as sun cheaters (cheaters being an American slang term for glasses).[1]

Most people find direct sunlight too bright for comfort during outdoor activities. Healthcare professionals recommend eye protection whenever the sun comes outbeach.

## History

### Precursors

Inuit snow goggles function by reducing exposure to sunlight, not by reducing its intensity

In prehistoric and historic time, Inuit peoples wore flattened walrus ivory “glasses,” looking through narrow slits to block harmful reflected rays of the sun.[3]

It is said that the Roman emperor [5]

James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century, around 1752. These were not “sunglasses” as that term is now used; Ayscough believed blue- or green-tinted glass could correct for specific vision impairments. Protection from the Sun's rays was not a concern for him.

Yellow/amber and brown-tinted spectacles were also a commonly prescribed item for people with syphilis in the 19th[dubious ] and early 20th centuries because sensitivity to light was one of the symptoms of the disease.

### Modern developments

In the early 1900s, the use of sunglasses started to become more widespread, especially among stars of movies. It is commonly believed that this was to avoid recognition by fans, but an alternative reason sometimes given is that they often had red eyes from the powerful [6]

Polaroid

Polaroid filter.

## Functions

### Visual clarity and comfort

Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare.[7]

Various types of disposable sunglasses are dispensed to patients after receiving eye examinations.

The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces such as water. They are popular among fishermen because they allow wearers to see into water when normally only glare would be seen.

The glare is neutralized by blocking the vertical (magnetic) components of light.

Broad temple arms protect against “stray light” entering from the sides

Sunglasses with slim temple arms

### Protection

Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.

The most widespread protection is against ultraviolet radiation, which can cause short-term and long-term ocular problems such as solar eclipse.

More recently, [12] Sunglasses are especially important for children, as their ocular lenses are thought to transmit far more HEV light than adults (lenses “yellow” with age).

There has been some speculation that sunglasses actually promote skin cancer.[13] This is due to the eyes being tricked into producing less melanocyte-stimulating hormone in the body.

#### Assessing the protection of sunglasses

The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Several standards for sunglasses (see below) allow a general classification of the UV protection (but not the blue light protection), and manufacturers often indicate simply that the sunglasses meet the requirements of a specific standard rather than publish the exact figures.

The only “visible” quality test for sunglasses is their fit. The lenses should fit close enough to the face that only very little “stray light” can reach the eye from their sides, or from above or below, but not so close that the eyelashes smear the lenses. To protect against “stray light” from the sides, the lenses should fit close enough to the temples and/or merge into broad temple arms or leather blinders.

It is not possible to “see” the protection that sunglasses offer. Dark lenses do not automatically filter out more harmful UV radiation and blue light as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider. As result, more unfiltered radiation enters the eye. Depending on the manufacturing technology, sufficiently protective lenses can block much or little light, resulting in dark or light lenses. The lens color is not a guarantee either. Lenses of various colors can offer sufficient (or insufficient) UV protection. Regarding blue light, the color gives at least a first indication: Blue blocking lenses are commonly yellow or brown whereas blue or gray lenses cannot offer the necessary blue light protection. However, not every yellow or brown lens blocks sufficient blue light. In rare cases, lenses can filter out too much blue light (i.e., 100%), which affects color vision and can be dangerous in traffic when colored signals are not properly recognized.

High prices cannot guarantee sufficient protection as no correlation between high prices and increased UV protection has been demonstrated. A 1995 study reported that “Expensive brands and polarizing sunglasses do not guarantee optimal UVA protection.”[16]

Protecting his eyes from exposure due to exophthalmos, sunglasses have become the trademark of German singer Heino

### Further functions of sunglasses

While non-tinted glasses are very rarely worn without the practical purpose of correcting eyesight or protecting one's eyes, sunglasses have become popular for several further reasons, and are sometimes worn even indoors or at night.

Sunglasses can be worn to hide one's eyes. They can make tells which involve eye movement and thus gain an advantage.

Fashion trends can be another reason for wearing sunglasses, particularly designer sunglasses. Sunglasses of particular shapes may be in vogue as a fashion accessory. Fashion trends can also draw on the “cool” image of sunglasses.

People may also wear sunglasses to hide an abnormal appearance of their eyes. This can be true for people with severe visual impairment, such as the nystagmus).

Some lawbreakers have also been known to wear sunglasses during or after committing a crime as an aid to hiding their identities.[17]

## Standards for sunglasses

There are three major sunglass standards, which are popularly known mostly as a reference for sunglass protection from UV radiation; the standards do, however, also include further requirements. A worldwide ISO standard does not yet exist, but by 2004, attempts to introduce such standard have led to a respective ISO standards committee, subcommittee, technical committee, and several working groups.[18] Sunglasses sold in the United States are regulated by the Food and Drug Administration and are required to conform to safety standards.

As of 2009, the European CE mark indicates that the glasses actually offer a safe level of Sun protection

The Australian Standard is AS/NZS 1067:2003 Sunglasses and fashion spectacles. The five ratings for transmittance (filter) under this standard are based on the amount of absorbed light, 0 to 4, with “0” providing some protection from UV radiation and sunglare, and “4” indicating a high level of protection, but not to be worn when driving. Australia introduced the world's first national standards for sunglasses in 1971. They were subsequently updated and expanded, leading in 1990 to AS 1067.1-1990 Sunglasses and fashion spectacles (incl. Part 1 Safety Requirements and Part 2 Performance Requirements), which was superseded in part in 2003 by AS/NZS 1067:2003 Sunglasses and fashion spectacles. The 2003 update made the Australian standard relatively similar to the European standard. This step opened the European market to Australian-made sunglasses, but the standard also maintained requirements considered specific to Australia's climate.[19]

The European standard EN 1836:2005 has four transmittance ratings: “0” for insufficient UV protection, “2” for sufficient UHV protection, “6” for good UHV protection and “7” for “full” UHVV protection, meaning that no more than 5% of the 380 nm rays are transmitted. Products which fulfill the standard receive a CE mark. There is no rating for transmittance protection for radiation of up to 400 nm (“UV400”), as required in other countries (incl. the United States) and recommended by experts.[9] The current standard EN 1836:2005 was preceded by the older standards EN 166:1995 (Personal eye protection –Specifications), EN167: 1995 (Personal eye protection – Optical test methods), and EN168: 1995 (Personal eye protection – Non-optical test methods), which in 2002 were republished as a revised standard under the name of EN 1836:1997 (which included two amendments). In addition to filtering, the standard also lists requirements for minimum robustness, labeling, materials (non-toxic for skin contact and not combustible) and lack of protrusions (to avoid harm when wearing them).[18]

The U.S. standard is [20]

## Special-use sunglasses

Sunglasses worn by an ocean kayaker

### Sunglasses in sports

As do corrective glasses, sunglasses have to meet special requirements when worn for sports. They need shatterproof and impact-resistant lenses; a strap or other fixing is typically used to keep glasses in place during sporting activities, and they have a nose cushion.

For water sports, so-called water sunglasses (also: surf water skiing.

Mountain climbing or traveling across glaciers or snowfields requires above-average eye protection, because sunlight (including ultraviolet radiation) is more intense in higher altitudes, and snow and ice reflect additional light. Popular glasses for this use are a type called glacier glasses or glacier goggles. They typically have very dark round lenses and leather blinders at the sides, which protect the eyes by blocking the Sun's rays around the edges of the lenses.

2006: Swedish astronaut International Space Station

### Sunglasses in space

Special protection is required for space travel because the sunlight is far more intense and harmful than on Earth, where it is always filtered through the [21]

The first sunglasses used in a Moon landing were the original [21]

## Construction

A range of sunglass models with lenses of different colors, for sale in Manhattan

Cult filmmaker Cannes Film Festival

### Lens

The color distortion, which could affect safety when, for instance, driving a car or a school bus.

• Gray and green lenses are considered neutral because they maintain true colors.
• Brown lenses cause some color distortion, but also increase contrast.
• Turquoise lenses are good for medium and high light conditions, because they are good at enhancing contrast, but do not cause significant color distortion.
• Orange and yellow lenses increase both contrast and depth perception. They also increase color distortion. Yellow lenses are used by pilots, boaters, fishers, shooters, and hunters for their contrast enhancement and width perception properties.[11]
• Blue or purple lenses are mainly cosmetic.

With the introduction of citation needed]

While some blue blocking sunglasses (see citation needed]

Some models have polarized lenses, made of diffuse sky radiation (skylight). This can be especially useful when fishing, for which the ability to see beneath the surface of the water is crucial.

A mirrorshades. A mirror coating does not get hot in sunlight and it prevents scattering of rays in the lens bulk.

Sunglass lenses are made of either glass, plastic, or SR-91. Plastic lenses are typically made from acrylic, polycarbonate, CR-39 or polyurethane. Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic lenses. They can also shatter or break on impact. Plastic lenses are lighter and shatter-resistant, but are more prone to scratching. Polycarbonate plastic lenses are the lightest, and are also almost shatterproof, making them good for impact protection. CR-39 is the most common plastic lens, due to low weight, high scratch resistance, and low transparency for ultraviolet and infrared radiation. SR-91 is a proprietary material that was introduced by Kaenon Polarized in 2001. Kaenon's lens formulation was the first non-polycarbonate material to pass the high-mass impact ANSI Z.87.1 testing.[26] Additionally, it was the first to combine this passing score with the highest marks for lens clarity. Jerry Garcia's sunglasses had a polykrypton-C type of lens which was ‘cutting edge' in 1995.

Any of the above features, color, polarization, gradation, mirroring, and materials, can be combined into the lens for a pair of sunglasses. Gradient glasses are darker at the top of the lens where the sky is viewed and transparent at the bottom. Photochromic lenses gradually darken when exposed to ultraviolet light.

This sunglass eyeshield uses a nylon half-frame and interchangeable lenses

Paul Newman wearing sunglasses indoors

### Frames

Frames are generally made of plastic, Oakley, for example, has straight resting hooks on all their glasses, preferring to call them “earstems”.

Frames can be made to hold the lenses in several different ways. There are three common styles: full frame, half frame, and frameless. Full frame glasses have the frame go all around the lenses. Half frames go around only half the lens; typically the frames attach to the top of the lenses and on the side near the top. Frameless glasses have no frame around the lenses and the ear stems are attached directly to the lenses. There are two styles of frameless glasses: those that have a piece of frame material connecting the two lenses, and those that are a single lens with ear stems on each side.

Some sports-optimized sunglasses have interchangeable lens options. Lenses can be easily removed and swapped for a different lens, usually of a different color. The purpose is to allow the wearer to easily change lenses when light conditions or activities change. The reasons are that the cost of a set of lenses is less than the cost of a separate pair of glasses, and carrying extra lenses is less bulky than carrying multiple pairs of glasses. It also allows easy replacement of a set of lenses if they are damaged. The most common type of sunglasses with interchangeable lenses has a single lens or shield that covers both eyes. Styles that use two lenses also exist, but are less common.

### Nose bridge

Nose bridges provide support between the lens and the face. They also prevent pressure marks caused by the weight of the lens or frame on the cheeks. People with large noses may need a low nose bridge on their sunglasses. People with medium noses may need a low or medium nose bridge. People with small noses may need sunglasses with high nose bridges to allow clearance.

## Fashion (alphabetically)

Aviator sunglasses

Mirrored aviators

Mirrored wrap-around sunglasses

Oversized sunglasses à la Jackie O

Original Ray-Ban Wayfarer

### Aviator sunglasses

Aviator sunglasses feature oversize teardrop-shaped lenses and a thin metal frame. The design was introduced in 1936 by Bausch & Lomb for issue to U.S. military aviators. As a fashion statement, aviator sunglasses are often made in mirrored, colored, and wrap-around styles.

In addition to pilots, Aviator-style sunglasses gained popularity with young people in the late 1960s and continue to be popular, with only a brief fall in demand during the 1990s.

### Clip-on glasses

Clip-on glasses are a form of tinted glasses that can be clipped on to eyeglasses for protection from the Sun. The best protection is polarized lens with 1.1mm. An alternative are flip-up glasses.

Gradient lenses go from a darker shade at the top to a lighter one at the bottom, so there will be more protection from sunlight the higher one looks through the lens, but the lower one looks through the lens, the less protection is offered. An advantage is that one can wear them indoors without fear of tripping over something and also allowing the user to see. Wearing sunglasses to nightclubs has become common in recent times, where the gradient lens comes in handy. Gradient lenses may also be advantageous for activities such as flying airplanes and driving automobiles, as they allow the operator a clear view of the instrument panel, low in his line of sight and usually hidden in shadow, while still reducing glare from the view out the windscreen. The Independent (London), has also referred to these style of sunglasses as the Murphy Lens.[27]

Double gradient lenses are dark at the top, light in the middle and dark at the bottom.

Gradients should not be confused with progressive lenses.

### Flip-up sunglasses

Flip-up sunglasses add the benefits of sunglasses to corrective eyeglasses, allowing the wearer to flip up the tinted lenses for indoor use. An alternative are clip-on glasses.

### Mirrored sunglasses

Mirrored lenses, having a metallic, partially reflective coating on the outer surface, combined with a tinted glass lens, are an alternative to polarization for UV protection, improving contrast when depth perception is important such as seeing moguls and ice while skiing or snowboarding. The mirrored lens reflects glare to protect the eyes, but improves the ability to see contrasts, and mirrored lenses of different colors can expand the range of fashion styles.

### Oversized sunglasses

Oversized sunglasses, which were fashionable in the 1980s, are now often used for humorous purposes. They usually come in bright colors with colored lenses and can be purchased cheaply.

The singer Elton John sometimes wore oversized sunglasses on stage in the mid-1970s as part of his Captain Fantastic act.

In the early twenty-first century moderately oversized sunglasses have become a fashion trend. There are many variations, such as the “Onassis”, discussed below, and Dior white sunglasses.

Onassis glasses or “Jackie O's” are very large sunglasses worn by women. This style of sunglasses is said to mimic the kind most famously worn by Jacqueline Kennedy Onassis in the 1960s. The glasses continue to be popular with women, and celebrities may use them, ostensibly to hide from paparazzi.

Oversized sunglasses, because of their larger frames and lenses, are useful for individuals who are trying to minimize the apparent size or arch of their nose.[28] Oversized sunglasses also offer more protection from sunburn due to the larger areas of skin they cover, although sunblock should still be used.

Shutter Shades were a fad in the early 1980s. Instead of tinted lenses, they decrease sun exposure by means of a set of parallel, horizontal shutters (like a small window shutter). Analogous to Inuit goggles (see above), the principle is not to filter light, but to decrease the amount of sun rays falling into the wearer's eyes. To provide UV protection, Shutter Shades sometimes use lenses in addition to the shutters; if not, they provide very insufficient protection against ultraviolet radiation and blue light.

“Teashades” (sometimes also called “John Lennon glasses”, “Round Metal”, or, occasionally, “Granny Glasses”) were a type of psychedelic art wire-rim sunglasses that were often worn, usually for purely aesthetic reasons, by members of the 1960s counterculture, as well as by opponents of segregation.[citation needed] Pop icons such as Mick Jagger, Roger Daltrey, John Lennon, Jerry Garcia, Boy George, Liam Gallagher and Ozzy Osbourne, all wore teashades. The original teashade design was made up of medium-sized, perfectly round lenses, supported by pads on the bridge of the nose and a thin wire frame. When teashades became popular in the late 1960s, they were often elaborated: Lenses were elaborately colored, mirrored, and produced in excessively large sizes, and with the wire earpieces exaggerated. A uniquely colored or darkened glass lens was usually preferred. Modern versions tend to have plastic lenses, as do many other sunglasses. Teashades are hard to find in shops today; however, they can still be found at many costume Web sites and in some countries.

The term has now fallen into disuse, although references can still be found in literature of the time. “Teashades” was also used to describe glasses worn to hide the effects of marijuana (conjunctival injection) or bloodshot eyes or the effects of opiates such as heroin (pupillary constriction).

The glasses worn by Lady Gaga have been seen wearing several variations of teashades. Howard Stern was also known for wearing teashades in the early to mid 90's and never taking them off in public. Unlike the others, Jerry Garcia actually created his own line of sunglasses in his name just before he passed away.

### Wayfarers

The Ray-Ban Wayfarer is a plastic-framed design for sunglasses produced by the Ray-Ban company. Introduced in 1952, the trapezoidal lenses are wider at the top than the bottom and were famously worn by James Dean, Roy Orbison and other actors and singers. The original frames were black; frames in many different colors were later introduced. There is always a silver piece on the corners as well.

### Wrap-around sunglasses

Wrap-arounds (sometimes also called “Yoko Ono glasses”) are a specific design of sunglasses. They are characterized by a single, smooth, semi-circular lens that covers both eyes and much of the same area of the face covered by protective goggles. The lens is usually combined with a minimal plastic frame and single piece of plastic serving as a nosepiece. As an alternative, the glasses can have two lenses, but the design evokes the same semicircle.

## Other names for sunglasses

There are various words referring to eyepieces with darkened lenses:

• Shades is probably the most widely used term for sunglasses in North America.
• Glares is a term popular in India if the glass is dark.
• Glints is a term for glasses originating from the “glint” that is noticeable when somebody wearing glasses moves their head.
• Sun spectacles is a term used by some opticians.
• Spekkies is a term used predominantly in southern Australia.
• Sun specs (also sunspecs) is the shortened form of sun spectacles.
• Sunglass a monocle version.[citation needed]
• Sun-shades can also refer to the sun-shading eyepiece-type, although the term is not exclusive to these. Also in use is the derivative abbreviation, shades.
• Dark glasses (also preceded by pair of) — generic term in common usage.
• Sunnies is Australian, South African, UK and New Zealand slang
• Smoked spectacles usually refers to the darkened eyepieces worn by blind people.
• Solar shields Usually refers to models of sunglasses with large lenses.
• Stunna shades Used as a slang term in the hyphy movement, usually referring to sunglasses with oversized lenses.
• Glecks is Scottish slang for glasses or sunglasses.
• Cooling glasses is a term used in Southern India (predominantly Kerala) and the Middle East for sunglasses.

## References

1. ^ Partridge, Eric (2006). The New Partridge Dictionary of Slang and Unconventional English. Tom Dalzell, Terry Victor. Routledge. p. 377.
2. ^ Ellis, Rachel (2010-06-01). “How making your child wear sunglasses could save their sight”. Eye Care Trust Organization UK. Daily Mail. Retrieved 2010-10-19.
3. ^
Acton, Johnny; Adams, Tania; Packer, Matt (2006). Jo Swinnerton. ed. Origin of Everyday Things. 1-4027-4302-5.
4. ^ “Pliny the Elder, The Natural History, Book XXXVII, Ch. 16”. Perseus.tufts.edu. Retrieved 2010-05-13.
5. ^ Ament, Phil (2006-12-04). “Sunglasses History – The Invention of Sunglasses”. The Great Idea Finder. Vaunt Design Group. Retrieved 2007-06-28.
6. ^
7. ^ Sakamoto Y., Sasaki K., Kojima M., Sasaki H., Sakamoto A., Sakai M., Tatami A. “The effects of protective eyewear on hair and crystalline lens transparency. Dev Ophthalmol. 2002;35:93-103. PMID 12061282.
8. . Retrieved 2010-05-13.
9. ^ Karlsruhe (retrieved 21 September 2009)
Siegfried Hünig (2008). Optimierter Lichtschutz der Augen. Eine dringende Aufgabe und ihre Lösung. Teil 1: Beschaffenheit des Lichts, innere und äußere Abwehrmechanismen. [Optimized protection from light-inflicted eye damage. A pressing problem and a simple solution]. Zeitschrift für praktische Augenheilkunde, 29, pp. 111-116.
Siegfried Hünig (2008). Optimierter Lichtschutz der Augen. Teil 2: Sehprozess als Risikofaktor, Lichtschutz durch Brillen [Optimized protection from light-inflicted eye damage. A pressing problem and a simple solution]. Zeitschrift für praktische Augenheilkunde, 29, pp. 197-205.
10. ^ Glazer-Hockstein C, Dunaief JL. “Could blue light-blocking lenses decrease the risk of age-related macular degeneration?” Retina. 2006 Jan;26(1):1-4. doi:10.1097/00006982-200601000-00001 PMID 16395131
Margrain TH, Boulton M, Marshall J, Sliney DH. “Do blue light filters confer protection against age-related macular degeneration?” Prog Retin Eye Res. 2004 Sep;23(5):523-31. PMID 15302349
11. ^ “Information from Your Eye M.D.: Sunglasses.” November 2003.
12. ^ article by Charlotte Remé, who also developed the guidelines/norms for Switzerland:
Remé, Charlotte (1997). Lichtschutz der Augen. [Light protection for Eyes] Der informierte Arzt – Gazette Medicale, 18, pp. 243-246
13. ^ “Sunglasses Raise Risk of Cancer”. Express.co.uk. 2007-06-03. Retrieved 2010-05-13.
14. ^ Leow YH, Tham SN. “UV-protective sunglasses for UVA irradiation protection.” Int J Dermatol. 1995 Nov;34(11):808-10. PMID 8543419.
15. ^ “Sunglasses and fashion spectacles—April 2003”. Accc.gov.au. . Retrieved 2010-05-13.
16. ^ – Some Sunglasses Are Cheap In Price Only
17. ^ “10 most wanted bank robbery suspects”. ABC Local. 2012-09-19. Retrieved 2012-11-26. “In each of the instances, the female suspect wore a distinctive wig and sunglasses to conceal her identity.”
18. ^ no author (2004). Requirements of European Directives and Standards Relating to Sunglasses.. Retrieved 21 September 2009.
19. ^ no author (2002). Public eye looks over new standard for sunglasses (2002-01-20). website of Standards Australia. Retrieved 21 September 2009.
20. ^ MB Optics Safety (2006). The ANSI Z87.1-2003 standard. Retrieved 22 June 2011.
21. ^ NASA website (retrieved on 21 September 2009)
22. ^ http://www.silhouette-international.com/silhouette/press/meilensteine_eng.doc
23. ^ Optikum, Unabhängiges Augenoptik-Panorama. “optikum, UNABHÄNGIGES AUGENOPTIK-PANORAMA – Silhouette Titan Minimal Art Space Edition – Die leichteste Brille des Universums”. Optikum.at. Retrieved 2010-05-13.
24. ^ “”no author” (”no date”). American Optical Flight Gear Vintage Sunglasses. on ”AAA Pilot Supplies” (retrieved on 21 September 2009)”. Aaapilots.com. 1969-07-20. . Retrieved 2010-05-13.
25. ^ no author (2006). Look Sharp While Seeing Sharp. (Originating Technology/NASA Contribution). Spinoff 2006, NASA Scientific and Technical Information (STI). Retrieved 17 October 2009.
26. ^ Welcome To Pech Optical
28. ^ Recommended Type of Sunglasses for People with Large Nose

# Melanism

The black panther is the prototypical example of melanism.

Melanistic Guinea pigs are relatively rare, and considered especially effective in ritual use by Andean curanderos.[1]

Melanism is a development of dark-colored [3]

Pseudo-melanism, also called abundism, is another variant of pigmentation, characterized by dark spots or enlarged stripes, which cover a large part of the body of the animal making it appear melanistic.[4] A deficiency in or total absence of melanin pigments is called amelanism.

The morbid deposition of black matter, is often of a malignant character, causing pigmented tumors is called melanosis.[5] For a description of melanin-related disorders see melanin, melanosis coli and ocular melanosis.

## Contents

Melanism related to the process of adaptation is called adaptive. Most commonly, dark individuals become fitter to survive and reproduce in their environment as they are better camouflaged. This makes some species less conspicuous to predators, while others such as black panthers use it as a foraging advantage during night hunting.[6] Typically, adaptive melanism is heritable: A dominant gene, which is entirely or nearly entirely expressed in the phenotype is responsible for the excessive amount of melanin.

Adaptive melanism has been shown to occur in a variety of animals, including mammals such as squirrels, many felines and canids, and coral snakes. Adaptive melanism can lead to the creation of morphs, the most notable example being the peppered moth whose evolutionary history in the United Kingdom is offered as a classic instructional tool for teaching the principles of natural selection.[7]

## Industrial melanism

Industrial melanism is adaptive melanism caused by anthropogenic alteration of the natural environment in terms of industrial pollution. As soot, smoke and other industrial pollutants from factories darken the landscape and because many organisms rely on camouflage to avoid predation, this sudden change in their environment makes them highly vulnerable to predators. This creates a strong selective pressure which will see any organism with a darker colour much more likely to survive and contribute to the gene pool of the next generation. Rare mutations are hence selected for and over time the population will adjust to a new equilibrium.[8] Peppered moth evolution is commonly used as an example of industrial melanism.

## In felines

Melanistic coat coloration occurs as a common polymorphism in 11 of 37 felid species and reaches high population frequency in some cases but never achieves complete fixation. The black panther, a melanic form of leopard, is common in the equatorial rainforest of Malaya and the tropical rainforest on the slopes of some African mountains such as Mount Kenya. The serval also has melanic forms in certain areas of East Africa. In the jaguarundi coloration varies from dark brown and gray to light reddish. Melanic forms of jaguar are common in certain parts of South America.[9] In 1938 and 1940, two melanistic bobcats were trapped alive in sub-tropical Florida.[10]

In 2003, the dominant mode of inheritance of melanism in jaguars was confirmed by performing phenotype transmission analysis in a 116-individual captive pedigree. Melanistic animals were found to carry at least one copy of a mutant MC1R sequence allele, bearing a 15-base pair inframe deletion. Ten unrelated melanistic jaguars were either homozygous or heterozygous for this allele. A 24-base pair deletion causes the incompletely dominant allele for melanism in the jaguarundi. Sequencing of the agouti signalling peptide in the agouti gene coding region revealed a 2-base pair deletion in black domestic cats. These variants were absent in melanistic individuals of Geoffroy’s cat, oncilla, pampas cat and Asian golden cat, suggesting that melanism arose independently at least four times in the cat family.[11]

Melanism in leopards is inherited as a [14]

## Immune system

Genetic research has shown that melanistic wolves owe their coloration to a mutation that first arose in domestic dogs

Melanin has several physiological roles in maintaining health, such as the synthesis of vitamin D. Melanin is the primary determinant of the degree of skin pigmentation and protects the body from harmful ultraviolet radiation. Synthesis of 1,25-dihydroxyvitamin D3 in the skin, however, is dependent on ultraviolet B light. Highly pigmented skin, to the level found in people of African origin, abrogates almost all ultraviolet-induced 1,25-(OH)2D3 synthesis. Numerous animal models and clinical studies have underlined the essential role of vitamin D as a modulator of the different processes of the immune system. Evidence indicates that serum concentrations of 1,25-(OH)2D3 and the prevalence of autoimmune diseases in a certain population are associated with the latitude at which that population resides.[15]

Genes for melanism in felines may provide resistance to viral infections. A viral epidemic may explain the prevalence of black leopards in Java and Malaysia, and the relatively high incidence of black leopards and black servals in the Aberdares region of Africa. Previously, black furred felines in the Aberdares had been considered a high altitude adaptation since black fur absorbs more heat.[16]

Studies reported in New Scientist magazine in 2003 also suggested that recessive-gene melanism is linked to disease resistance rather than altitude. Melanistic cats may have better resistance to disease than cats with “normal” color coats. This would explain why recessive melanism persists when melanistic individuals are disadvantaged because they are poorly camouflaged in open areas.

## Socio-politics

The term melanism has been used on usenet, internet forums and blogs to mean an African-American social movement holding that dark-skinned humans are in some measures superior to those of other skin colour. The term melanism has been used in this context as early as the mid-1990s[17] and was promoted by some Afrocentrists, such as Frances Cress Welsing.

## References

1. 0-8165-1558-1.
2. ^ Webster's Revised Unabridged Dictionary (1913) Melanism. C. & G. Merriam Co. Springfield, Massachusetts. Page 910
3. ^ Liddell, H. G., Scott, R. (1940). μελα^νός. In: A Greek-English Lexicon, revised and augmented throughout by Sir Henry Stuart Jones, with the assistance of Roderick McKenzie. Clarendon Press, Oxford.
4. ^ Osinga, N., Hart, P., van VoorstVaader, P. C. (2010). Albinistic common seals (Phoca vitulina) and melanistic grey seals (Halichoerus grypus) rehabilitated in the Netherlands. Animal Biology 60 (3): 273−281.
5. ^ Webster's Revised Unabridged Dictionary (1913) Melanosis. C. & G. Merriam Co. Springfield, Massachusetts. Page 910
6. ^ King, R.C., Stansfield, W.D., Mulligan, P.K. (2006). A Dictionary of Genetics, 7th ed., Oxford University Press
7. Ecology: From individuals to ecosystems. 4th ed., Blackwell Publishing Malden, Oxford, Victoria.
8. ^ Allaby, M. (1992) The Concise Oxford Dictionary of Zoology. Oxford University Press. New York.
9. ^ Searle, A. G. (1968) Comparative Genetics of Coat Colour in Mammals. Logos Press, London
10. ^ Ulmer, F. A. (1941) Melanism in the Felidae, with special reference to the Genus Lynx. Journal of Mammalogy 22 (3): 285–288.
11. http://www.pucrs.br/fabio/genomaenglish/index_arquivos/artigos_eduardo/Copy%20of%20Melanism_CB_reprint.pdf.
12. ^ Robinson, R. (1970). “Inheritance of black form of the leopard Panthera pardus”. Genetica 41: 190–197.
13. ^ Kawanishi, K., Sunquist, M. E., Eizirik, E., Lynam, A. J., Ngoprasert, D., Wan Shahruddin, W. N., Rayan, D. M., Sharma, D. S. K., Steinmetz, R. (2010) Near fixation of melanism in leopards of the Malay Peninsula. Journal of Zoology, Volume 282 (3): 201–206.
14. ^ Majerus, M. E. N. (1998) Melanism: evolution in action. Oxford University Press, New York
15. ^ Shoenfeld, N., Amital, H., Shoenfeld, Y. (2009). The effect of melanism and vitamin D synthesis on the incidence of autoimmune disease. Nature Reviews Rheumatology 5: 99−105.
16. ^ Seidensticker, J., Lumpkin, S. (2006). Smithsonian Q & A: the ultimate question and answer book. Cats. Collins, New York
17. ^ “Sundiata, AFROCENTRISM: THE ARGUMENT WE'RE REALLY HAVING.”. Retrieved 2007-06-23.

# UV-Light

## Ultraviolet (UV) comes in sunshine and from UV-lamps

UV light is found in chemical bonds in molecules, even without having enough energy to ionize atoms.

Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV on the skin, called vitamin D (peak production occurring between 295 and 297 nm) in all organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human health.

## Discovery

The discovery of UV radiation was associated with the observation that [4]

The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann.[5]

## Origin of the term

The name means “beyond violet” (from Latin ultra, “beyond”), violet being the color of the shortest wavelengths of visible light. UV light has a shorter wavelength than violet light.

## Subtypes

The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The ISO standard on determining solar irradiances (ISO-21348)[6] describes the following ranges:

Name Abbreviation Wavelength range
(in nanometres)
Energy per photon
(in electronvolts)
Notes / alternative names
Ultraviolet UV 400 – 100 nm 3.10 – 12.4 eV
Ultraviolet A UVA 400 – 315 nm 3.10 – 3.94 eV long wave, black light
Ultraviolet B UVB 315 – 280 nm 3.94 – 4.43 eV medium wave
Ultraviolet C UVC 280 – 100 nm 4.43 – 12.4 eV short wave, germicidal
Near Ultraviolet NUV 400 – 300 nm 3.10 – 4.13 eV visible to birds, insects and fish
Middle Ultraviolet MUV 300 – 200 nm 4.13 – 6.20 eV
Far Ultraviolet FUV 200 – 122 nm 6.20 – 10.16 eV
Hydrogen Lyman-alpha H Lyman-α 122 – 121 nm 10.16– 10.25 eV
Extreme Ultraviolet EUV 121 – 10 nm 10.25 – 124 eV
Vacuum Ultraviolet VUV 200 – 10 nm 6.20 – 124 eV

Vacuum UV is so-named because it is absorbed strongly by air, and is therefore used in a vacuum. In the long-wave limit of this region, roughly 150 – 200 nm, the principal absorber is the oxygen in air. Work in this region can be performed in an oxygen-free atmosphere (commonly pure nitrogen), avoiding the need for a vacuum chamber.

## Sources of UV

### Natural sources and filters of UV

Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC is blocked by dioxygen (from 100–200 nm) or by ozone (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone and most of it reaches the ground.

The sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm (see false color photograph of the Sun in extreme ultraviolet beginning this article). Extremely hot stars emit proportionally more UV radiation than the Sun. For example, the star R136a1 has a thermal energy of 4.57 eV, which falls in the near-UV range (optically, such stars appear blue-white rather than violet).

[9]

Since with the Sun at zenith the Earth's air and ozone layer allows passage of a total of 32 watts/m2 (ground UV power) out of a vacuum value of about 140 watts/m2 (i.e., 23%) of Sun's UV light, this is equivalent to a minimal atmospheric blockage of 77% of the Sun's UV. However, most of the Sun's UV that is blocked by Earth's atmosphere lies in the shorter UV wavelengths. The figure rises to 97–99% of the Sun's UV radiation at the average mixture of other Sun angles encountered through the day.[10]

The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air. Of the ultraviolet radiation that reaches the Earth's surface, up to 95% is UVA (the very longest wavelength),[11] depending on cloud cover and atmospheric conditions.

Ordinary glass is partially [14]

### Artificial sources of UV

#### “Black lights”

Two black light fluorescent tubes, showing use. The top is a F15T8/BLB 18 inch, 15 watt tube, used in a standard plug-in fluorescent fixture. The bottom is an F8T5/BLB 12 inch, 8 watt tube, used in a portable battery-powered black light sold as a pet urine detector.

A black light is a lamp that emits long-wave UVA radiation. Some types filter out visible light by using selective-pass wood's glass. Fluorescent black light lamps employ UVA phosphor blends and constructed in the same fashion as normal fluorescent lights. BLB type lamps use filtering glass which is deep-bluish-purple optical filter which blocks almost all visible light above 400 nanometres.[15] The color of such lamps is often referred to in the lighting industry as “blacklight blue” or “BLB”, to distinguish them from UV lamps used in “bug zapper” insect traps, that do not have the optical filter coating. These are designated “blacklight” (“BL”) lamps. The phosphor typically used for a near 368 to 371 nanometre emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+), whereas the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate (BaSi2O5:Pb+). “Blacklight Blue” lamps peak at 365 nm.

A black light may also be formed, very inefficiently, by simply using mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass are also made, in ratings up to 1 kW, used mainly for theatrical and concert displays.

Some UV fluorescent bulbs specifically designed to attract insects use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Plain glass blocks less of the visible mercury emission spectrum, making them appear light-blue to the naked eye. These lamps are referred to as “blacklight” or “BL” in most lighting catalogs.

#### Short wave ultraviolet lamps

9 watt germicidal UV lamp, in compact fluorescent (CF) form factor

Lamps which emit short wave UV light are also made. citation needed]. The quartz tube is doped with an additive to block the 185 nm wavelength. These “germicidal” lamps are used extensively for disinfection of surfaces in laboratories and food processing industries, and for sterilizing water supplies.

Standard bulbs have an optimum operating temperature of about 30 degrees Celsius. Use of a mercury amalgam allows operating temperature to rise to 100 degrees Celsius, and UVC emission to about double or triple per unit of light-arc length. These low-pressure lamps have a typical efficiency of approximately thirty to thirty-five percent, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–35 watts of total UV output. UVA/UVB emitting bulbs also sold for other special purposes, such as reptile-keeping.

#### Gas-discharge lamps

Specialized UV gas-discharge lamps are sold, containing a variety of different gases, to produce UV light at particular spectral lines for scientific purposes. Argon and deuterium lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride.[16] These are often the light sources in UV spectroscopy equipment for chemical analysis.

#### Ultraviolet LEDs

Light-emitting diodes (LEDs) can be manufactured to emit light in the ultraviolet range, although practical LED arrays are very limited below 365 nm. LED efficiency at 365 nm is about 5–8%, whereas efficiency at 395 nm is closer to 20%, and power outputs at these longer UV wavelengths are also better. Such LED arrays are beginning to be used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. Power densities approaching 3 W/cm2 (30 kW/m2) are now possible, and this, coupled with recent developments by photoinitiator and resin formulators, makes the expansion of LED-cured UV materials likely.

A 380 nanometre UV LED makes some common household items fluoresce.

#### Ultraviolet lasers

UV solid-state lasers can be manufactured to emit light in the ultraviolet range.

The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam which is mostly UV. The strongest lines are at 337.1 nm wavelength in the ultraviolet. Other lines have been reported at 357.6 nm, also ultraviolet. (This laser also emits weaker lines in blue, red, and infrared)

Direct UV-emitting laser diodes are available at 375 nm.optical storage).

## Detecting and measuring UV radiation

Ultraviolet detection and measurement technology can vary with the part of the spectrum under consideration. While some silicon detectors are used across the spectrum, and in fact the US NIST has characterized simple silicon diodes[19] that work with visible light too, many specializations are possible for different applications. Many approaches seek to adapt visible light-sensing technologies, but these can suffer from unwanted response to visible light and various instabilities. A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Ultraviolet light can be detected by suitable photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are available.

### Near and medium UV

A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers.

Between 200 and 400 nm, a variety of detector options exist. Photographic film detects near UV coming from blue sky as “violet” as far as the glass optics of cameras will permit which is usually to about 350 nm. For outdoor film photography, in fact, slightly yellow UV filters are often standard equipment in order to prevent unwanted bluing and overexposure by UV light that the eye does not see (these filters are also convenient lens scratch protectors). For photography only in the near UV, special filters may be used. For UV with wavelengths shorter than 350 nm, usually special quartz lens systems must be used, which do not absorb the radiation.

Digital cameras use sensors that are usually sensitive to UV, but some have internal filters that block it, in order to present images in truer color as they would be seen by the eye. Some of these systems may be adapted by removing the internal UV filter, and adding an external visible light filter. Others have no internal filter and can be used unmodified for near-UV photography, with only use of an external visible light filter. A few systems are designed for use in the UV. (See ultraviolet photography).

People cannot perceive UV light directly since the [21]

### Vacuum UV

Vacuum UV or VUV (wavelengths shorter than 200 nm) is blocked by air but can propagate through a vacuum. These wavelengths are strongly absorbed by molecular oxygen in the air. Pure nitrogen (with less than about 10 ppm oxygen) is transparent to wavelengths in the range of about 150 – 200 nm. This has practical significance, since semiconductor manufacturing processes have been using wavelengths shorter than 200 nm. By working in oxygen-free gas, the equipment does not have to be built to withstand vacuum. Some other scientific instruments that operate in this spectral region, such as circular dichroism spectrometers, are also commonly nitrogen-purged.

Technology for VUV instrumentation was largely driven by solar astronomy physics for many decades, but more recently some Marchywka Effect).

### Extreme UV

Extreme UV (EUV) is characterized by a transition in the physics of interaction with matter: wavelengths longer than about 30 nm interact mainly with the chemical valence electrons of matter, whereas shorter wavelengths interact mainly with inner-shell electrons and nuclei. The long end of the EUV/XUV spectrum is set by a prominent He+ spectral line at 30.4 nm. XUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50% of XUV radiation at normal incidence. This technology, which was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, has been used to make telescopes for solar imaging (current examples are SOHO/EIT and TRACE), and equipment for nanolithography (printing of very small-scale traces and devices on microchips).

## Human health-related effects of UV radiation

The health effects ultraviolet radiation has on fluorescent lamps and health.

### Beneficial effects

#### Vitamin D

UVB exposure induces the production of vitamin D in the skin at a rate of up to 1,000 IUs per minute. The majority of positive health effects are related to this vitamin. It has regulatory roles in calcium metabolism (which is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density), immunity, cell proliferation, insulin secretion, and blood pressure.[22]

#### Aesthetics

Too little UVB radiation may lead to a lack of vitamin D. Too much UVB radiation may lead to skin color) leads to a limited amount of direct DNA damage. This is recognized and repaired by the body, then melanin production is increased, which leads to a long-lasting tan. This tan occurs with a 2-day lag phase after irradiation.

#### Medical applications

Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as [24]

### Harmful effects

An overexposure to UVB radiation can cause [27]

UVC rays are the highest energy, most dangerous type of ultraviolet light.

On 13 April 2011 the International Agency for Research on Cancer of the World Health Organization classified all categories and wavelengths of ultraviolet radiation as a Group 1 carcinogen. This is the highest level designation for carcinogens and means “There is enough evidence to conclude that it can cause cancer in humans”.

Ultraviolet photons harm the thymine dimer” makes a bulge, and the distorted DNA molecule does not function properly.

#### Skin

##### Cancer risk
 “ Ultraviolet (UV) irradiation present in sunlight is an environmental human immunosuppression. ” — Matsumura and Ananthaswamy , (2004)[28]

UVA, UVB, and UVC can all damage [31]

Because UVA does not cause reddening of the skin (erythema), it is not measured in the usual types of [33]

The reddening of the skin due to the action of sunlight depends both on the amount of sunlight and on the sensitivity of the skin (“erythemal action spectrum”) over the UV spectrum.

UVB light can cause direct DNA damage. As noted above UVB radiation ozone depletion and the ozone hole.

As a defense against UV radiation, the type and amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present, and it triggers the release of the melanin from melanocytes. However, because this process does not increase the total amount of melanin, a UVA-produced tan is largely cosmetic and does not protect against either sun burn or UVB-produced DNA damage or cancer.[34]

By contrast, UVB yields a slower tan that requires roughly two days to develop, because the mechanism of UVB tanning is to stimulate the body to produce more melanin. However, the production of melanin by UV, called [36]

##### Sunscreen safety debate

Image of a man's face with sunscreen on the left, in visible (left) and UV light, demonstrating how sunscreen protects against UV exposure. The side of the face with sunscreen is darker, showing that the sunscreen absorbs the UV light.

Medical organizations recommend patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors (see sunscreen).

However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.[42]

The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.

In an experiment by Hanson et al. published in 2006, the amount of harmful reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the amount of ROS was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high, the amount of ROS was higher in the sunscreen treated skin than in the untreated skin.[35]

Such effects can be avoided by using newer generations of filter substances or combinations that maintain their UV protective properties even after several hours of solar exposure. Sunscreen products containing photostable filters like drometrizole trisiloxane, bisoctrizole, or bemotrizinol have been available for many years throughout the world, but are not yet available in the U.S., whereas another high-quality filter, ecamsule, has also been available in the U.S. since 2006.[36]

##### Aggravation of skin diseases

Ultraviolet radiation causes aggravation of several skin conditions and diseases, including:

#### Eye

High intensities of UVB light are hazardous to the eyes, and exposure can cause pinguecula formation.

UV light is absorbed by molecules known as retina can be damaged.

Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. Given that light may reach the eye from the sides, full coverage eye protection is usually warranted if there is an increased risk of exposure, as in high altitude mountaineering. Mountaineers are exposed to higher than ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice.

Ordinary, untreated polycarbonate, inherently block most UV. There are protective treatments available for eyeglass lenses that need it, which will give better protection. But even a treatment that completely blocks UV will not protect the eye from light that arrives around the lens.

## Degradation of polymers, pigments and dyes

UV damaged polypropylene rope (left) and new rope (right)

Many sunlight. The problem appears as discoloration or fading, cracking, and, sometimes, total product disintegration if cracking has proceeded sufficiently. The rate of attack increases with exposure time and sunlight intensity.

It is known as UV degradation, and is one form of polymer degradation. Sensitive polymers include thermoplastics, such as polypropylene, polyethylene, and poly(methyl methacrylate) as well as speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. They include tertiary carbon atoms, which in polypropylene occur in every repeat unit. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength. The impact of UV on polymers is used in nanotechnology, transplantology, X-ray lithography and other fields for modification of properties (roughness, hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet (VUV).[46]

IR spectrum showing carbonyl absorption due to UV degradation of polyethylene

In addition, many watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV light. Tinted glasses, such as sunglasses also provide protection from UV rays.

## Blockers and absorbers

Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (UV degradation (photo-oxidation) of a material. A number of different UVAs with different absorption properties exist. UVAs can disappear over time, so monitoring of UVA levels in weathered materials is necessary.

In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone and octyl methoxycinnamate, are known as absorbers. They are contrasted with physical “blockers” of UV radiation such as titanium dioxide and zinc oxide. (See sunscreen for a more complete list.)

## Applications of UV

By wavelength:[47]

### Imaging

#### Fire detection

Ultraviolet detectors generally use either a solid-state device, such as one based on Earth's atmosphere. The result is that the UV detector is “solar blind”, meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.

UV detectors are sensitive to most fires, including X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.

#### Checking high voltage electrical insulation by corona discharge detection

An application of UV is to detect corona discharge (often called “corona”) on electrical apparatus. Degradation of insulation in electrical apparatus or pollution causes corona, wherein a strong electric field ionizes the air and excites nitrogen molecules, causing the emission of ultraviolet radiation. The corona degrades the insulation level of the apparatus. Corona produces ozone and to a lesser extent nitrogen oxide, which may subsequently react with water in the air to form nitrous acid and nitric acid vapour in the surrounding air.[49]

### Use of sources

#### Fluorescent lamps

mercury vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.

The main mercury emission wavelength is in the UVC range. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous.

The light from a mercury lamp is predominantly at discrete wavelengths. Other practical UV sources with more continuous emission spectra include mercury-xenon arc lamps, metal-halide arc lamps, and tungsten-halogen incandescent lamps.

#### Lasers

Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology and keratectomy), chemistry (MALDI), free air secure communications and computing (optical storage). They can be made by applying frequency conversion to lower-frequency lasers, or from Ce:LiSAF crystals (cerium doped with lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory.[18]

### Fluorescent dye related uses

#### Fluorescent optical brighteners

Colorless fluorescent dyes that emit blue light under UV are added as textile finishing agents. These ubiquitous dyes are the reason for the bright blue fluorescence of many papers and fabrics under UV. The extra blue light emitted by these agents counteracts yellow tints that may be present, and causes the colors and whites to appear whiter or (if colored) more brightly and purely colored.

UV fluorescent dyes that glow in the primary color of paints, papers and textiles, also are used to enhance the color of these materials.

#### Paints

Paints that contain dyes that glow under UV are used in a number of art and esthetic applications.

#### Security

A bird appears on many Visa credit cards when they are held under a UV light source

To help prevent Visa stamps and stickers on passports of visitors contain large detailed seals made of such inks, that are invisible under normal light, but strongly visible under UV illumination. Many passports have UV-sensitive (fluorescent) watermarks on all pages. Currencies of various countries' banknotes have an image, as well as many multicolored fibers, that are visible only under ultraviolet light.

Some brands of pepper spray will leave an invisible chemical (UV dye) that is not easily washed off on a pepper-sprayed attacker, which would help police identify them later.[50]

### Analytic uses

#### Forensics

UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood and saliva.UV-Vis microspectroscopy is also used to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.

#### Authentication

In other detective work including authentication of various collectibles and art, and detecting counterfeit currency even absent of UV-fluorescent marker dyes (for use of such dyes, see “security” section above). Even unmarked materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short-wave ultraviolet versus long-wave ultraviolet.

#### Reading otherwise illegible papyri and manuscripts

Using multi-spectral imaging it is possible to read illegible papyrus, such as the burned papyri of the Villa of the Papyri or of Oxyrhynchus, or the Archimedes palimpsest. The technique involves taking pictures of the illegible document using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion can be found for distinguishing ink from paper on the papyrus surface. Simple NUV sources can be used to highlight faded iron-based ink on vellum.[53]

#### Chemical markers

UV fluorescent genetics as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of use and interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.

#### Sanitary compliance

Ultraviolet light aid in the detection of organic mineral deposits that remain on surfaces where periodic cleaning and sanitizing may not be properly accomplished. Both urine and phosphate soaps are easily detected using UV inspection. Pet urine deposits in carpeting or other hard surfaces can be detected for accurate treatment and removal of mineral tracers and the odor-causing bacteria that feed on proteins within. Many hospitality industries use UV lamps to inspect for unsanitary bedding to determine lifecycle for mattress restoration as well as general performance of the cleaning staff.[citation needed] A perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.

#### Analyzing minerals

A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.

Ultraviolet lamps are also used in analyzing fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet.

### Material science uses

#### Photolithography

Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The light causes chemical reactions to occur in the photoresist, and, after development (a step that removes either the exposed or the unexposed photoresist), a pattern determined by the mask remains on the sample. Steps may then be taken to “etch” away, deposit on or otherwise modify areas of the sample where no photoresist remains.

UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components,[54] and printed circuit boards.

Photolithography processes (Processes used to fabricate electronic integrated circuits) especially make use of Extreme Ultraviolet radiations. For example, the microprocessor manufacturing processes implemented by major companies such as Intel, AMD, Qualcomm make use of EUV light pencil to draw elecronic circuits on silicon wafers at subatomic scales. Latest microprocessor devices manufactured in this way have their onchip integrated circuitry of 22 nm size (latest process technology by Intel as of 2012). Other integrated chip manufacturing processes help fabricate electronic chips of standard sizes of 32 nm, 45 nm, 65 nm. Going forward the thickness of electronic circuits on these chips would further come down to 14 nm and then to thickness range of 7 nm, 5 nm and 4 nm. Reducing the thickness of circuits on silicon wafer chips provide advantages of low power usage, lesser heating and faster response time along with providing faster circuitry on smaller form factors (miniaturization). All this becomes possible using EUV-based photolithographic processes.

#### Curing of electronic potting resins

Electronic components that require clear transparency for light to exit or enter (photo voltaic panels and sensors) can be potted using acrylic resins that are cured using UV light energy. The advantages are low VOC emissions and rapid curing.

#### Curing of inks, adhesives, varnishes and coatings

Certain inks, coatings, and printing, and dental fillings. Curing of decorative finger nail “gels”.

An industry has developed around the manufacture of UV sources for UV curing applications. This includes Fe (iron, doped)-based bulbs are used, which can be energized with electric arc or microwaves. Lower-power sources (fluorescent lamps, LED) can be used for static applications, and, in some cases, small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.

#### Erasing EPROM modules

Some flash memory chips in most devices.

#### Preparing low surface energy polymers

UV radiation is useful in preparing low surface energy surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger.

#### UV solar cells and UV degradation of solar cells

Japan's National Institute of Advanced Industrial Science and Technology (AIST) has succeeded in developing a transparent solar cell that uses ultraviolet light to generate electricity but allows visible light to pass through it. Most conventional solar cells use visible and infrared light to generate electricity. In contrast, the innovative new solar cell uses ultraviolet radiation. Used to replace conventional window glass, the installation surface area could be large, leading to potential uses that take advantage of the combined functions of power generation, lighting and temperature control.[55]

Also PEDOT-PSS solar cells is an ultraviolet (UV) light-selective and -sensitive photovoltaic cell easily fabricated.[56]

On the other hand, a nanocrystalline layer of Cu2O in the construction of photovoltaic cells increases their ability to utilize UV radiations for photocurrent generation.[57]

#### Nondestructive testing

UV light of a specified spectrum and intensity is used to stimulate fluorescent dyes so as to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (magnetic particle inspection).

#### Postage stamps

Postage stamps are tagged with a phosphor which glows under UV light (the U.S. uses short wave UV) to permit automatic detection of the stamp and facing of the letter.

### Biology related uses

#### Air purification

Using a spores into harmless inert byproducts. The cleansing mechanism of UV is a photochemical process. The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. These compounds break down when exposed to high-intensity UV at 240 to 280 nm. Short-wave ultraviolet light can destroy DNA in living microorganisms and break down organic material found in indoor air. UVC's effectiveness is directly related to intensity and exposure time.

UV light has also been shown (by KJ Scott et al) as effective in reducing gaseous contaminants such as iron oxides remove the ozone produced by the UV lamp.

#### Microbial sterilization

A low pressure mercury vapor discharge tube floods the inside of a sterilizing microbiological contaminants from irradiated surfaces.

Ultraviolet lamps are used to dimerize; if enough of these defects accumulate on a microorganism's DNA, its replication is inhibited, thereby rendering it harmless (even though the organism may not be killed outright). However, since microorganisms can be shielded from ultraviolet light in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.

#### Disinfecting drinking water

UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection is the process of using PET bottles and sunlight to disinfect water. Ultraviolet germicidal irradiation is the generic process to inactivate microorganisms in water, air, medical environments etc.

New York City has approved the construction of a 2.2 billion US gallon per day (535,000 m3/hr) ultraviolet drinking water disinfection facility due to be online in 2012.[63]

It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens that have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. The findings resulted in the use of UV radiation as a viable method to treat drinking water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation.[64] It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.

Solar water disinfection[65] (SODIS) has been extensively researched in Switzerland and has proven ideal to treat small quantities of water cheaply using natural sunlight. Contaminated water is poured into transparent plastic bottles and exposed to full sunlight for six hours. The sunlight treats the contaminated water through two synergetic mechanisms: UV-A irradiation and increased water temperature. If the water temperatures rises above 50 °C (120 °F), the disinfection process is three times faster.

#### Food processing

As consumer demand for fresh and “fresh-like” food products increases, the demand for nonthermal methods of food processing is likewise on the rise. In addition, public awareness regarding the dangers of food poisoning is also raising demand for improved food processing methods. Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV light can be used to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet light source.[66] The effectiveness of such a process depends on the UV absorbance of the juice (see Beer's law).

#### Biological surveys and pest control

Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet light. Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on a yellow to green color under UV illumination, thus assisting in the control of these arachnids. Many birds have patterns in their plumage that are invisible at usual wavelengths but observable in ultraviolet, and the urine and other secretions of some animals, including dogs, cats, and human beings, is much easier to spot with ultraviolet. Urine trails of rodents can be detected by pest control technicians for proper treatment of infested dwellings.

Butterflies use ultraviolet as a communication system for sex recognition and mating behavior.

Many insects use the ultraviolet wavelength emissions from celestial objects as references for flight navigation. A local ultraviolet emitter will normally disrupt the navigation process and will eventually attract the flying insect.

Entomologist using a UV light for collecting Chaco.

Ultraviolet traps called faunistic survey studies.

#### Photochemotherapy

Exposure to UVA light while the skin is hyper-photosensitive by taking PUVA may be used only a limited number of times over a patient's lifetime.

#### Phototherapy

Exposure to UVB light, in particular, the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like [68]

Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and repeated sessions may be required before results are noticeable. Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. Home UVB systems are common solutions for those whose conditions respond to treatment. Home systems permit patients to treat themselves every other day (the ideal treatment regimen for most) without the frequent, costly trips to the office/clinic and back.

Side-effects may include itching and redness of the skin due to UVB exposure, and possibly sunburn, if patients do not minimize exposure to natural UV rays during treatment days. Cataracts can frequently develop if the eyes are not protected from UVB light exposure. To date, there is no link between an increase in a patient's risk of skin cancer and the proper use of narrow-band UVB phototherapy.[70] “Proper use” is generally defined as reaching the “Sub-Erythemic Dose” (S.E.D.), the maximum amount of UVB your skin can receive without burning. Certain fungal growths under the toenail can be treated using a specific wavelength of UV delivered from a high-power LED (light-emitting diode) and can be safer than traditional systemic drugs.

Note that this is different from phototherapy for physiological neonatal jaundice in infants, which uses blue light, not UV.

#### Herpetology

Reptiles need long wave UV light for de novo synthesis of vitamin D. Vitamin D is needed to metabolize calcium for bone and egg production. Thus, in a typical reptile enclosure, a fluorescent UV lamp should be available for vitamin D synthesis. This should be combined with the provision of heat for basking, either in the same or by another lamp.

[75]

## Evolutionary significance

Evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet light. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy (see picture above). This leads to frameshifting during genetic replication and protein synthesis, usually killing the organism. As early prokaryotes began to approach the surface of the ancient oceans, before the protective ozone layer had formed, blocking out most wavelengths of UV light, they almost invariably died out. The few that survived had developed enzymes that verified the genetic material and broke up thymine dimer bonds, known as base excision repair enzymes. Many enzymes and proteins involved in modern mitosis and meiosis are similar to excision repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome UV light.[76]

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