False-color image of the Sun's corona as seen in deep ultraviolet by the Extreme ultraviolet Imaging Telescope
Black light fluorescent tubes, a common source of long wave (UVA) ultraviolet.



UV light is found in sunlight and is emitted by electric arcs and specialized lights such as black lights. It can cause chemical reactions, and causes many substances to glow or fluoresce. Most ultraviolet is classified as non-ionizing radiation. The higher energies of the ultraviolet spectrum from about 150 nm ('vacuum' ultraviolet) are ionizing, but this type of ultraviolet is not very penetrating and is blocked by air.[1]





Origin of the term



The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The draft ISO standard on determining solar irradiances (ISO-DIS-21348)[4] describes the following ranges:

Name Abbreviation Wavelength range in nanometers Energy per photon
Before UV spectrum Visible light above 400 nm below 3.10 eV
Near NUV 400 nm–300 nm 3.10–4.13 eV
Middle MUV 300 nm–200 nm 4.13–6.20 eV
Far FUV 200 nm–122 nm 6.20–10.2 eV
Vacuum VUV 200 nm–100 nm 6.20–12.4 eV
Low LUV 100 nm–88 nm 12.4–14.1 eV
Super SUV 150 nm–10 nm 8.28–124 eV
Extreme EUV 121 nm–10 nm 10.2–124 eV
Beyond UV range X-rays below 10 nm above 124 eV

In photolithography and laser technology, the term deep ultraviolet or DUV refers to wavelengths below 300 nm. Extreme Ultraviolet stands here for discrete spectral ranges of around 13.5 nm (in future planned also 6.x nm) of about 2 % bandwidth. In fields like analytics and life sciences, the acronym "XUV" is used for Extreme Ultraviolet for characterizing the broader spectral range, such as to distinguish from EUV. XUV is separated from x-rays and VUV, by the fact that the photoelectron ionization of innershell electrons is the - by orders of magnitudes - dominating photon-matter interaction effect. This is in contrast to x-rays, where scatter is relevant and VUV where the interaction is mainly with outer ("chemical active") electrons of the atoms and molecules.

"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, pure nitrogen being commonly used, which avoids the need for a vacuum chamber.


Sources of UV

Natural sources of UV





"Black lights"


A black light, Wood's light, or UV light is a lamp that emits long-wave UV radiation and very little visible light. Fluorescent black lights are typically made in the same fashion as normal fluorescent lights, except that a different phosphor is used on the inside of the tube which emits UV instead of visible light, and the clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, 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 blue Wood's glass. 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+) while 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.

While "black lights" do produce light in the UV range, their spectrum is confined to the long-wave UVA region. Unlike UVB and UVC, which are responsible for the direct DNA damage that leads to skin cancer, black light is limited to lower-energy, longer waves and does not cause sunburn, although it can damage collagen fibers and destroy vitamins A and D in skin.[citation needed]

A black light may also be formed, very inefficiently, by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. This was the method used to create the very first black light sources. Though cheaper than the fluorescent source, only 0.1% of the input power is converted to usable radiation, as the incandescent light radiates as a black body with very little emission in the UV. Incandescent bulbs used to generate significant UV, due to their inefficiency, may become dangerously hot. More rarely still, high-power (hundreds of watts) mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass are made, are used mainly for theatrical and concert displays. They also become very hot during normal use.


Ultraviolet fluorescent lamps

Fluorescent lamps without a phosphorescent coating to convert UV to visible light, emit ultraviolet light with two peaks at 253.7 nm and 185 nm due to the peak emission of the mercury within the bulb. Eighty-five to ninety percent of the UV produced by these lamps is at 253.7 nm, while only five to ten percent is at 185 nm. Germicidal lamps use quartz (glass) doped with an additive to block the 185 nm wavelength. With the addition of a suitable phosphor (phosphorescent coating) , they can be modified to produce a UVA, UVB, or visible light spectrum (all fluorescent tubes used for domestic and commercial lighting are mercury (Hg) UV emission bulbs at heart).

Such low-pressure mercury lamps are used extensively for disinfection, and in standard form 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, it will produce approximately 30-35 watts of total UV output. UVA/UVB emitting bulbs also sold for other special purposes, such as reptile-keeping.

Ultraviolet LEDs


Ultraviolet lasers


Gas-discharge lamps


Detecting and measuring UV radiation


Near UV


Vacuum UV


Human health-related effects of UV radiation


Beneficial effects

Vitamin D




Medical applications


Harmful effects

An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. However the most deadly form - malignant melanoma - is mostly caused by the indirect DNA damage (free radicals and oxidative stress). This can be seen from the absence of a UV-signature mutation in 92% of all melanoma.[15] In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system.[16] Moreover, UVC can cause adverse affects that can variously be mutagenic or carcinogenic.[17]





Cancer risk
— Matsumura and Ananthaswamy , (2004)[18]

UVA, UVB, and UVC can all damage collagen fibers and, therefore, accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.[19] In the past, UVA was considered less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species). It penetrates deeply, but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA.[citation needed] Because it does not cause reddening of the skin (erythema), it cannot be measured in SPF testing.[citation needed] There is no good clinical measurement for blockage of UVA radiation, but it is important for sunscreen to block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma risk found for sunscreen users.[20]


UVB light can cause direct DNA damage. The radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent cytosine bases, producing a dimer. When DNA polymerase comes along to replicate this strand of DNA, it reads the dimer as "AA" and not the original "CC". This causes the DNA replication mechanism to add a "TT" on the growing strand. This mutation can result in cancerous growths, and is known as a "classical C-T mutation". The mutations caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers. The mutagenicity of UV radiation can be easily observed in bacterial cultures. This cancer connection is one reason for concern about ozone depletion and the ozone hole. UVB causes some damage to collagen, but at a very much slower rate than UVA.[citation needed]

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 yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.[citation needed] The photochemical properties of melanin make it an excellent photoprotectant. Older and more widespread sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin, and, therefore, the penetration of these sunscreen ingredients into the lower layers of the skin may increase the amount of free radicals and reactive oxygen species (ROS).[21] In recent years, improved filtering substances have come into use in commercial sunscreen lotions that do not significantly degrade or lose their capacity to protect the skin as the exposure time increases (photostable substances).[22]

Sunscreen prevents the direct DNA damage that causes sunburn by blockage of UVB.[clarification needed] As such, most of these products contain an SPF rating that indicates how well they block UVB as a measure of their effectiveness. This rating, however, offers no data about protection against UVA, exposure to which does not lead to sunburn but is still harmful.[citation needed] In the US, the Food and Drug Administration is considering adding a star rating system to show UVA protection. A similar system is already used in some European countries.[citation needed] Some sunscreen lotions now include compounds such as titanium dioxide, which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone.

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.


However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.[23][24][25] The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough to cause damage. In one study of sunscreens, the authors write:[26]




Aggravation of skin diseases



High intensities of UVB light are hazardous to the eyes, and exposure can cause welder's flash (photokeratitis or arc eye) and may lead to cataracts, pterygium,[28][29] and pinguecula formation.




Degradation of polymers, pigments and dyes




IR spectrum showing carbonyl absorption due to UV degradation of polyethylene


Blockers and absorbers



Applications of UV

By wavelength:[31]


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

To help prevent counterfeiters, sensitive documents (e.g., credit cards, driver's licenses, passports) may also include a UV watermark that is visible only under a UV-emitting light. Passports issued by most countries usually contain UV sensitive inks and security threads. Visa stamps and stickers on passports of visitors contain large detailed seals invisible under normal light, but strongly visible under UV illumination. Passports issued by many nations have UV sensitive 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.[33]


UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids (semen, blood,[citation needed] bile etc.). E.g., ejaculated fluids or saliva are detected by high-power UV, irrespective of the structure or colour of the surface the fluid is deposited upon.[34]

Fluorescent lamps







Biological surveys and pest control








Sanitary compliance


Air purification


UV light has also been shown (by KJ Scott et al) as effective in reducing gaseous contaminants such as carbon monoxide and VOCs.[35][36][37] Scott and his colleagues demonstrated that the correct mixture of UV lamps radiating at 184 and 254 nm can remove low concentrations of hydrocarbons and carbon monoxide, if the lamps are held in a radiation chamber (a box or drum) and the air is recycled between the room and the reaction chamber. This arrangement prevents the introduction of ozone into the treated air. Alternatively, air may be treated by passing by a single UV source operating at 184 nm and subsequent catalysis with iron pentaoxide. The iron oxides remove the ozone produced by the UV lamp.

Analyzing minerals




In other detective work including authentication of various collectibles and art, and detecting counterfeit currency absent of marker dyes. 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.

Chemical markers







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. There is no link between an increase in the patient's risk for skin cancer and the proper use of UVB phototherapy.[40] "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.




UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components,[41] and printed circuit boards.

Checking electrical insulation





Disinfecting drinking water


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.[43] There are also several facilities under construction and several in operation that treat waste water with several stages of filters, hydrogen peroxide, and UV light to bring the water up to drinking standards. One such facility exists in Orange County, California which is designed to treat wastewater and convert it into high-quality water for Indirect Potable Reuse.[44][45] NASA has examined the use of this technology, using titanium dioxide as catalyst, for breaking down harmful products in spacecraft waste water.[46]



Food processing


Fire detection





Curing of electronic potting resins


Curing of inks, adhesives, varnishes and coatings



Sun tanning

Sun tanning describes a darkening of the skin in a natural physiological response stimulated by exposure to ultraviolet radiation from sunshine (or a sunbed). With excess exposure to the sun, a suntanned area can also develop sunburn. The increased production of melanin is triggered by the direct DNA damage.[50] This kind of damage is recognized by the body and as a defense against UV radiation the skin produces more melanin. Melanin dissipates the UV energy as harmless heat, and therefore it is an excellent photoprotectant. Melanin protects against the direct DNA damage and against the indirect DNA damage. Sunscreen protects only against the direct DNA damage, but increases the indirect DNA damage.[23][24][25] Some studies suggest that this may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users.[51][52][20][53][54]

Erasing EPROM modules


Preparing low surface energy polymers


Reading otherwise illegible papyruses and manuscripts




UV solar cells and UV degradation of solar cells




Nondestructive testing


Evolutionary significance


See also


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  39. ^ "UVB Phototherapy" (php). National Psoriasis Foundation, USA. Archived from the original on 2007-06-22. http://web.archive.org/web/20070622180124/http://www.psoriasis.org/treatment/psoriasis/phototherapy/uvb.php. Retrieved 2007-09-23. 
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