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.
The discovery of UV radiation was associated with the observation that 
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.
|Energy per photon
|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
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).
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.
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), depending on cloud cover and atmospheric conditions.
Ordinary glass is partially 
Artificial sources of UV
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. 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
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.
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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. These are often the light sources in UV spectroscopy equipment for chemical analysis.
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.
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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 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
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 
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 (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).
The health effects ultraviolet radiation has on fluorescent lamps and health.
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.
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.
Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as 
An overexposure to UVB radiation can cause 
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 (UV) irradiation present in sunlight is an environmental human immunosuppression.||”|
— Matsumura and Ananthaswamy , (2004)
UVA, UVB, and UVC can all damage 
Because UVA does not cause reddening of the skin (erythema), it is not measured in the usual types of 
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.
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 
Sunscreen safety debate
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.
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.
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.
Aggravation of skin diseases
Ultraviolet radiation causes aggravation of several skin conditions and diseases, including:
- Systemic lupus erythematosus
- Sjögren’s syndrome
- Sinear Usher syndrome
- Darier’s disease
- Kindler-Weary syndrome.
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
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).
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
- 13.5 nm: Extreme Ultraviolet Lithography
- 30–200 nm: ultraviolet photoelectron spectroscopy
- 230–365 nm: UV-ID, label tracking, barcodes
- 230–400 nm: Optical sensors, various instrumentation
- 240–280 nm: DNA absorption has a peak at 260 nm)
- 200–400 nm: Forensic analysis, drug detection
- 270–360 nm: drug discovery
- 280–400 nm: cells
- 300–320 nm: Light therapy in medicine
- 300–365 nm: printer inks
- 300–400 nm: Solid-state lighting
- 350–370 nm: 
In space observatory.)
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.
Use of sources
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.
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.
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 that contain dyes that glow under UV are used in a number of art and esthetic applications.
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.
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.
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.
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.
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. 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.
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
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.
- 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.
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 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.
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.
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.
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. It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.
Solar water disinfection (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.
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. 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.
Ultraviolet traps called faunistic survey studies.
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.
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Exposure to UVB light, in particular, the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like 
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. “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.
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.
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.
- Black light
- High-energy visible light
- Infrared light
- Polymer degradation
- Risks and benefits of sun exposure
- Sun tanning
- Tanning lamp
- Titanium dioxide
- Ultraviolet blood irradiation
- Ultraviolet light and cancer
- Ultraviolet photography
- UV degradation
- UV index
- UV stabilizers in plastics
- Weather testing of polymers
- Wood's lamp
- “HPS.org”. HPS.org. http://www.hps.org/publicinformation/ate/q2111.html. Retrieved 2011-11-08.
- “Reference Solar Spectral Irradiance: Air Mass 1.5”. http://rredc.nrel.gov/solar/spectra/am1.5/. Retrieved 2009-11-12.
- 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.
- “ISO 21348 Process for Determining Solar Irradiances”. http://www.spacewx.com/Docs/ISO_PRF_21348_e.pdf.
- Solar radiation
- Solar constant at ground level
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