View source for Physics:Ultraviolet

{{Short description|Energetic, invisible light energy range}}
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'''Ultraviolet''' ('''UV''') light is [[Physics:Electromagnetic radiation|electromagnetic radiation]] in a range of energies higher than that of [[Physics:Visible light|visible light]], but less than [[Physics:X-ray|X-ray]]s. UV radiation is present in [[Astronomy:Sunlight|sunlight]], and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by [[Physics:Electric arc|electric arc]]s; [[Physics:Cherenkov radiation|Cherenkov radiation]]; and specialized lights, such as [[Physics:Mercury-vapor lamp|mercury-vapor lamp]]s, [[Physics:Tanning lamp|tanning lamp]]s, and black lights. 

Although long-wavelength ultraviolet is not considered an [[Physics:Ionizing radiation|ionizing radiation]] because its [[Physics:Photon|photon]]s lack the energy to [[Physics:Ionization|ionize]] [[Physics:Atom|atom]]s, it can cause [[Chemistry:Chemical reaction|chemical reaction]]s and causes many substances to glow or [[Biology:Fluorescence|fluoresce]]. Many practical applications, including chemical and biological effects, derive from the way that UV radiation can interact with organic molecules. These interactions can involve [[Physics:Absorption (electromagnetic radiation)|absorption]] or adjusting energy states in molecules, but do not necessarily involve heating. {{citation needed|date=January 2023}}

Short-wave ultraviolet light damages [[Biology:DNA|DNA]] and sterilizes surfaces with which it comes into contact. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of [[Medicine:Skin cancer|skin cancer]]. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the [[Astronomy:Atmosphere|atmosphere]].<ref>{{cite web |url=http://missionscience.nasa.gov/ems/10_ultravioletwaves.html |title=Reference Solar Spectral Irradiance: Air Mass 1.5 |access-date=2009-11-12 |url-status=dead |archive-url=https://web.archive.org/web/20110127004149/http://missionscience.nasa.gov/ems/10_ultravioletwaves.html |archive-date=27 January 2011}}</ref> More energetic, shorter-wavelength "extreme" UV below 121&nbsp;nm ionizes air so strongly that it is absorbed before it reaches the ground.<ref>{{cite journal |last=Haigh |first=Joanna D. |date=2007 |title=The Sun and the Earth's Climate: Absorption of solar spectral radiation by the atmosphere |journal=Living Reviews in Solar Physics |volume=4 |issue=2 |pages=2 |doi=10.12942/lrsp-2007-2 |bibcode=2007LRSP....4....2H|doi-access=free }}</ref> However, ultraviolet light (specifically, UVB) is also responsible for the formation of [[Chemistry:Vitamin D|vitamin D]] in most land [[Biology:Vertebrate|vertebrate]]s, including humans.<ref>{{cite journal |last1=Wacker |first1=Matthias |last2=Holick |first2=Michael F. |date=2013-01-01 |title=Sunlight and Vitamin D|journal=Dermato-endocrinology |volume=5 |issue=1 |pages=51–108 |doi=10.4161/derm.24494 |issn=1938-1972 |pmc=3897598 |pmid=24494042}}</ref> The UV spectrum, thus, has effects both beneficial and harmful to life.

The lower wavelength limit of the [[Physics:Visible spectrum|visible spectrum]] is conventionally taken as 400&nbsp;nm, so ultraviolet rays are not visible to humans, although people can sometimes perceive light at shorter wavelengths than this.<ref name='hambling'/> Insects, birds, and some mammals can see near-UV (NUV), i.e., slightly shorter wavelengths than what humans can see.<ref>{{Cite journal |last1=Cronin |first1=Thomas W. |last2=Bok |first2=Michael J. |date=2016-09-15 |title=Photoreception and vision in the ultraviolet |url=https://journals.biologists.com/jeb/article/219/18/2790/15420/Photoreception-and-vision-in-the-ultraviolet |journal=Journal of Experimental Biology |language=en |volume=219 |issue=18 |pages=2790–2801 |doi=10.1242/jeb.128769 |pmid=27655820 |hdl=11603/13303 |s2cid=22365933 |issn=1477-9145 |access-date=23 June 2022 |archive-date=24 June 2022 |archive-url=https://web.archive.org/web/20220624211939/https://journals.biologists.com/jeb/article/219/18/2790/15420/Photoreception-and-vision-in-the-ultraviolet |url-status=live |doi-access=free |hdl-access=free }}</ref>

==Visibility==
Ultraviolet rays are usually invisible to most humans. The [[Biology:Lens (vertebrate anatomy)|lens of the human eye]] blocks most radiation in the wavelength range of 300–400&nbsp;nm; shorter wavelengths are blocked by the [[Medicine:Cornea|cornea]].<ref>{{cite journal |title=Violet and blue light blocking intraocular lenses: photoprotection versus photoreception|journal=British Journal of Ophthalmology |year=2006 |volume=90 |pages=784–792 |author=M A Mainster |pmc=1860240 |pmid=16714268 |doi=10.1136/bjo.2005.086553 |issue=6}}</ref> Humans also lack [[Biology:Cone cell|color receptor]] adaptations for ultraviolet rays. Nevertheless, the [[Biology:Photoreceptor cell|photoreceptors]] of the [[Biology:Retina|retina]] are sensitive to near-UV, and people lacking a lens (a condition known as aphakia) perceive near-UV as whitish-blue or whitish-violet.<ref name='hambling'>{{cite news |title=Let the light shine in |author=David Hambling |newspaper=The Guardian |date=29 May 2002 |url=https://www.theguardian.com/science/2002/may/30/medicalscience.research |access-date=2 January 2015 |url-status=live |archive-url=https://web.archive.org/web/20141123170913/http://www.theguardian.com/science/2002/may/30/medicalscience.research |archive-date=23 November 2014}}</ref> Under some conditions, children and young adults can see ultraviolet down to wavelengths around 310&nbsp;nm.<ref name="LynchLivingston2001">{{cite book |last1=Lynch |first1=David K. |last2=Livingston |first2=William Charles |title=Color and Light in Nature |url=https://books.google.com/books?id=4Abp5FdhskAC&pg=PA231 |access-date=12 October 2013 |edition=2nd |year=2001 |publisher={{wipe|Cambridge University Press}} |location=Cambridge |isbn=978-0-521-77504-5 |page=231 |quote=Limits of the eye's overall range of sensitivity extends from about 310 to 1050 nanometers|url-status=live |archive-url=https://web.archive.org/web/20131231214332/http://books.google.com/books?id=4Abp5FdhskAC&pg=PA231 |archive-date=31 December 2013}}</ref><ref name="Dash2009">{{cite book |last1=Dash |first1=Madhab Chandra|last2=Dash|first2=Satya Prakash|title=Fundamentals of Ecology 3E|url=https://books.google.com/books?id=7mW4-us4Yg8C&pg=PA213|access-date=18 October 2013|year=2009|publisher=Tata McGraw-Hill Education|isbn=978-1-259-08109-5|page=213|quote=Normally the human eye responds to light rays from 390 to 760 nm. This can be extended to a range of 310 to 1,050 nm under artificial conditions.|url-status=live|archive-url=https://web.archive.org/web/20131231214338/http://books.google.com/books?id=7mW4-us4Yg8C&pg=PA213|archive-date=31 December 2013}}</ref> Near-UV radiation is visible to insects, some mammals, and some [[Biology:Bird vision|birds]]. Birds have a fourth color receptor for ultraviolet rays; this, coupled with eye structures that transmit more UV gives smaller birds "true" UV vision.<ref>{{cite web|url=http://io9.gizmodo.com/want-ultraviolet-vision-youre-going-to-need-smaller-ey-1468759573 |website=Gizmodo |title=Want ultraviolet vision? You're going to need smaller eyes|first=Joseph|last=Bennington-Castro|date=22 November 2013 |url-status=live|archive-url=https://web.archive.org/web/20160507082220/http://io9.gizmodo.com/want-ultraviolet-vision-youre-going-to-need-smaller-ey-1468759573|archive-date=7 May 2016}}</ref><ref name="HuntCarvalho2009">{{cite journal|last1=Hunt|first1=D. M.|last2=Carvalho|first2=L. S.|last3=Cowing|first3=J. A.|last4=Davies|first4=W. L.|title=Evolution and spectral tuning of visual pigments in birds and mammals|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=364|issue=1531|year=2009|pages=2941–2955|issn=0962-8436|doi=10.1098/rstb.2009.0044 |doi-access=free |pmid=19720655|pmc=2781856}}</ref>
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== History and discovery ==
"Ultraviolet" means "beyond violet" (from [[Social:Latin|Latin]] ''ultra'', "beyond"), violet being the color of the highest frequencies of [[Physics:Light|visible light]]. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light.

UV radiation was discovered in 1801 when the German physicist [[Biography:Johann Wilhelm Ritter|Johann Wilhelm Ritter]] observed that invisible rays just beyond the violet end of the visible spectrum darkened [[Chemistry:Silver chloride|silver chloride]]-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" ({{lang-de|de-oxidierende Strahlen}}) to emphasize [[Chemistry:Reactivity|chemical reactivity]] and to distinguish them from "[[Physics:Infrared|heat rays]]", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably [[Biography:John William Draper|John William Draper]], who named them "tithonic rays"<ref>"On a new Imponderable Substance and on a Class of Chemical Rays analogous to the rays of Dark Heat", J.W. Draper, The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 1842, LXXX, pp.453–461</ref><ref>"Description of the Tithonometer", J.W. Draper, The Practical Mechanic and Engineer's Magazine, January 1844, pp.122–127</ref>). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and [[Physics:Infrared|infrared]] [[Physics:Radiation|radiation]], respectively.<ref>{{cite book|last1=Beeson|first1=Steven|last2=Mayer|first2=James W|title=Patterns of light: chasing the spectrum from Aristotle to LEDs|publisher=Springer|location=New York|isbn=978-0-387-75107-8|page=149|chapter=12.2.2 Discoveries beyond the visible|date=2007-10-23}}</ref><ref name="hockberger">
{{Cite journal
 | last = Hockberger
 | first = Philip E.
 | title = A history of ultraviolet photobiology for humans, animals and microorganisms
 | journal = Photochem. Photobiol.
 | volume = 76
 | issue = 6
 | pages = 561–79
 | year = 2002
 | doi = 10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2
 | pmid = 12511035
| s2cid = 222100404
 }}</ref> In 1878, the sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903,  the most effective wavelengths were known to be around 250&nbsp;nm. In 1960, the effect of ultraviolet radiation on DNA was established.<ref>James Bolton, Christine Colton, ''The Ultraviolet Disinfection Handbook'', American Water Works Association, 2008 {{ISBN|978 1 58321 584 5}}, pp. 3–4</ref>

The discovery of the ultraviolet radiation with wavelengths below 200&nbsp;nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by German physicist [[Biography:Victor Schumann|Victor Schumann]].<ref name="Lyman">The [[Physics:Ozone layer|ozone layer]] also protects living beings from this.
{{Cite journal
 | last = Lyman
 | first = T.
 | title = Victor Schumann
 | journal = The Astrophysical Journal
 | volume = 38
 | pages = 1–4
 | year = 1914
 | bibcode = 1914ApJ....39....1L
 | doi = 10.1086/142050
 | doi-access = free
 }}</ref>

==<span class="anchor" id="UVA"></span><span class="anchor" id="UVB"></span><span class="anchor" id="UVC"></span><span class="anchor" id="Far UVC"></span><span class="anchor" id="NUV"></span><span class="anchor" id="MUV"></span><span class="anchor" id="FUC"></span><span class="anchor" id="FUV"></span><span class="anchor" id="Lyman-α"></span><span class="anchor" id="VUV"></span><span class="anchor" id="Vacuum UV"></span><span class="anchor" id="EUV"></span><span class="anchor" id="hard"></span><span class="anchor" id="soft"></span>Subtypes==

The [[Physics:Electromagnetic spectrum|electromagnetic spectrum]] of ultraviolet radiation (UVR), defined most broadly as 10–400&nbsp;nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO 21348:<ref>
{{cite web
 | title = ISO 21348 Definitions of Solar Irradiance Spectral Categories
 | website = Space Weather (spacewx.com)
 | url = http://www.spacewx.com/pdf/SET_21348_2004.pdf
 | url-status = dead  | access-date = 25 August 2013
 | archive-url = https://web.archive.org/web/20131029233428/http://www.spacewx.com/pdf/SET_21348_2004.pdf
 | archive-date = 29 October 2013
}}
</ref>

{| class="wikitable" style="margin:2em auto; text-align:center;"
|-
! Name
! Abbreviation
! [[Wavelength]] <br />(nm)
! [[Physics:Photon energy|Photon energy]] <br />(eV, aJ)
! Notes/alternative names
|-
| colspan="5" style="background:lightgrey" |
|-
| Ultraviolet A
| UV‑A
| 315–400
| {{convert|3.10|–|3.94|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Long-wave&nbsp;UV, [[Physics:Blacklight|blacklight]], not absorbed by the [[Physics:Ozone layer|ozone layer]]: soft&nbsp;UV.
|-
| Ultraviolet B
| UV‑B
| 280–315
| {{convert|3.94|–|4.43|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Medium-wave&nbsp;UV, mostly absorbed by the ozone layer: intermediate&nbsp;UV; Dorno radiation.
|-
| Ultraviolet C
| UV‑C
| 100–280
| {{convert|4.43|–|12.4|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Short-wave&nbsp;UV, [[Physics:Ultraviolet germicidal irradiation|germicidal]]&nbsp;UV, [[Physics:Ionizing radiation|ionizing radiation]] at shorter wavelengths, completely absorbed by the ozone layer and atmosphere: hard&nbsp;UV.
|-
| colspan="5" style="background:lightgrey" |
|-
| Near ultraviolet
| N‑UV
| 300–400
| {{convert|3.10|–|4.13|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Visible to birds, insects, and fish.
|-
| Middle ultraviolet
| M‑UV
| 200–300
| {{convert|4.13|–|6.20|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" |
|-
| Far ultraviolet
| F‑UV
| ''122–200''
| {{convert|6.20|–|10.16|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | [[Physics:Ionizing radiation|Ionizing radiation]] at shorter wavelengths.
|-
| Hydrogen<br />[[Physics:Lyman-alpha line|Lyman-alpha]]
| H&nbsp;Lyman‑α
| 121–122
| {{convert|10.16|–|10.25|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Spectral line at 121.6&nbsp;nm, 10.20&nbsp;eV.
|-
| [[Physics:Extreme ultraviolet|Extreme ultraviolet]]
| E‑UV
| 10–121
| {{convert|10.25|–|124|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Entirely [[Physics:Ionizing radiation|ionizing radiation]] by some definitions; completely absorbed by the atmosphere.
|-
| colspan="5" style="background:lightgrey" |
|-
| Vacuum ultraviolet
| V-UV
| 10–200
| {{convert|6.20|–|12.4|eV|aJ|abbr=values|disp=x|, }}
| style="text-align:left;" | Strongly absorbed by atmospheric oxygen, though 150–200&nbsp;nm wavelengths can propagate through nitrogen.
|}

Several solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Many approaches seek to adapt visible light-sensing devices, but these can suffer from unwanted response to visible light and various instabilities. Ultraviolet can be detected by suitable [[Physics:Photodiode|photodiode]]s and [[Chemistry:Photocathode|photocathode]]s, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive UV [[Physics:Photomultiplier|photomultiplier]]s are available. [[Physics:Spectrometer|Spectrometer]]s and [[Physics:Radiometer|radiometer]]s are made for measurement of UV radiation. Silicon detectors are used across the spectrum.<ref>
{{cite journal
 |last1=Gullikson  |first1=E.M.      |last2=Korde  |first2=R.
 |last3=Canfield   |first3=L.R.      |last4=Vest   |first4=R.E.
 |year=1996
 |title=Stable silicon photodiodes for absolute intensity measurements in the VUV and soft X-ray regions
 |journal=Journal of Electron Spectroscopy and Related Phenomena
 |volume=80  |pages=313–316
 |doi=10.1016/0368-2048(96)02983-0
 |url=http://ts.nist.gov/MeasurementServices/Calibrations/upload/JES-80.PDF
 |access-date=2011-11-08
 |archive-url=https://web.archive.org/web/20090109215922/http://ts.nist.gov/MeasurementServices/Calibrations/upload/JES-80.PDF
 |archive-date=2009-01-09
}}
</ref>

Vacuum UV, or VUV, wavelengths (shorter than 200&nbsp;nm) are strongly absorbed by molecular [[Chemistry:Oxygen|oxygen]] in the air, though the longer wavelengths around 150–200&nbsp;nm can propagate through [[Chemistry:Nitrogen|nitrogen]]. Scientific instruments can, therefore, use this spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers. Significant examples include 193-nm [[Engineering:Photolithography|photolithography]] equipment (for semiconductor manufacturing) and [[Physics:Circular dichroism|circular dichroism]] spectrometers.

Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general; detectors can be limited by their response to non-VUV radiation, and the development of [[Engineering:Solar-blind technology|solar-blind devices]] has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.

Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30&nbsp;nm interact mainly with the outer [[Physics:Valence electron|valence electron]]s of atoms, while wavelengths shorter than that interact mainly with inner-shell electrons and nuclei. The long end of the EUV spectrum is set by a prominent He<sup>+</sup> spectral line at 30.4&nbsp;nm. EUV is strongly absorbed by most known materials, but synthesizing multilayer optics that reflect up to about 50% of EUV radiation at normal incidence is possible. This technology was pioneered by the [[Astronomy:NIXT|NIXT]] and [[Astronomy:MSSTA|MSSTA]] sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the [[Astronomy:Extreme Ultraviolet Explorer|Extreme Ultraviolet Explorer]] <!-- (EUVE) --> [[Astronomy:Satellite|satellite]].

Some sources use the distinction of "hard UV" and "soft UV". For instance, in the case of [[Physics:Astrophysics|astrophysics]], the boundary may be at the [[Physics:Lyman limit|Lyman limit]] (wavelength 91.2&nbsp;nm), with "hard UV" being more energetic;<ref>
{{cite book
 |first1=John |last1=Bally
 |first2=Bo |last2=Reipurth
 |year=2006
 |title=The Birth of Stars and Planets
 |page=177
 |publisher=Cambridge University Press
}}
</ref> the same terms may also be used in other fields, such as cosmetology, optoelectronic, etc. The numerical values of the boundary between hard/soft, even within similar scientific fields, do not necessarily coincide; for example, one applied-physics publication used a boundary of 190&nbsp;nm between hard and soft UV regions.<ref>
{{cite journal
 |last1=Bark     |first1=Yu B.    |last2=Barkhudarov   |first2=E.M.
 |last3=Kozlov   |first3=Yu N.    |last4=Kossyi        |first4=I.A.
 |last5=Silakov  |first5=V.P.     |last6=Taktakishvili |first6=M.I.
 |last7=Temchin  |first7=S.M.
 |year=2000
 |title=Slipping surface discharge as a source of hard UV radiation
 |journal=Journal of Physics D: Applied Physics
 |volume=33  |number=7  |pages=859
 |bibcode=2000JPhD...33..859B  |doi=10.1088/0022-3727/33/7/317
|s2cid=250819933 }}
</ref>

==Solar ultraviolet==
[[File:Ozone altitude UV graph.svg|thumb|upright=1.35|Levels of ozone at various altitudes (DU/km) and blocking of different bands of ultraviolet radiation: In essence, all UVC is blocked by diatomic oxygen (100–200&nbsp;nm) or by ozone (triatomic oxygen) (200–280&nbsp;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. UVA makes up almost all UV light that penetrates the Earth's atmosphere.]]
Very hot objects emit UV radiation (see [[Astronomy:Black-body radiation|black-body radiation]]). The [[Astronomy:Sun|Sun]] emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10&nbsp;nm. Extremely hot [[Astronomy:Star|star]]s (such as O- and B-type) emit proportionally more UV radiation than the Sun. [[Astronomy:Sunlight|Sunlight]] in space at the top of Earth's atmosphere (see [[Astronomy:Solar constant|solar constant]]) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m<sup>2</sup> in vacuum.<ref>{{cite web|title=Solar radiation |url=http://curry.eas.gatech.edu/Courses/6140/ency/Chapter3/Ency_Atmos/Radiation_Solar.pdf |archive-url=https://web.archive.org/web/20121101070344/http://curry.eas.gatech.edu/Courses/6140/ency/Chapter3/Ency_Atmos/Radiation_Solar.pdf|archive-date=1 November 2012|url-status=live}}</ref>

The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared.<ref>{{cite web|title=Introduction to Solar Radiation|url=http://www.newport.com/Introduction-to-Solar-Radiation/411919/1033/content.aspx |website=newport.com|url-status=live|archive-date=29 October 2013|archive-url=https://web.archive.org/web/20131029234117/http://www.newport.com/Introduction-to-Solar-Radiation/411919/1033/content.aspx}}</ref><ref>{{cite web|title=Reference Solar Spectral Irradiance: Air Mass 1.5|url=http://rredc.nrel.gov/solar/spectra/am1.5/|access-date=2009-11-12|url-status=live|archive-url=https://web.archive.org/web/20130928011257/http://rredc.nrel.gov/solar/spectra/am1.5/ASTMG173/ASTMG173.xls|archive-date=28 September 2013}}</ref> Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. Almost no UVC reaches the Earth's surface.<ref name="Skin Cancer Foundation">{{citation|url=http://www.skincancer.org/prevention/uva-and-uvb/understanding-uva-and-uvb|title=Understanding UVA and UVB|access-date=2012-04-30|url-status=live|archive-url=https://web.archive.org/web/20120501231522/http://www.skincancer.org/prevention/uva-and-uvb/understanding-uva-and-uvb|archive-date=1 May 2012}}</ref> The fraction of UVA and UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. On "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by [[Physics:Rayleigh scattering|Rayleigh scattering]] in the same way as the visible blue light from those parts of the sky. UVB also plays a major role in plant development, as it affects most of the plant hormones.<ref name="Vanhaelewyn et al. 2016">{{citation|url=https://academic.oup.com/jxb/article/67/15/4469/1750169|archive-url=https://web.archive.org/web/20160708010101/https://academic.oup.com/jxb/article/67/15/4469/1750169|title=Hormone-controlled UV-B responses in plants|url-status=dead|archive-date=8 July 2016}}</ref> During total overcast, the amount of absorption due to clouds is heavily dependent on the thickness of the clouds and latitude, with no clear measurements correlating specific thickness and absorption of UVA and UVB.<ref>{{Cite journal|last1=Calbó |first1=Josep|last2=Pagès|first2=David|last3=González|first3=Josep-Abel|date=2005|title=Empirical studies of cloud effects on UV radiation: A review |journal=Reviews of Geophysics|language=en|volume=43|issue=2|at=RG2002 |doi=10.1029/2004RG000155|bibcode=2005RvGeo..43.2002C |issn=1944-9208|hdl=10256/8464|s2cid=26285358 |hdl-access=free}}</ref>

The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the [[Physics:Ozone layer|ozone layer]] when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air.

== Blockers, absorbers, and windows ==
Ultraviolet absorbers are molecules used in organic materials ([[Chemistry:Polymers|polymers]], paints, etc.) to absorb UV radiation to reduce the [[Physics:UV degradation|UV degradation]] (photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary.

In [[Chemistry:Sunscreen|sunscreen]], ingredients that absorb UVA/UVB rays, such as [[Chemistry:Avobenzone|avobenzone]], [[Chemistry:Oxybenzone|oxybenzone]]<ref>{{cite journal |last1=Burnett |first1=M. E. |last2=Wang |first2=S. Q. |year=2011 |title=Current sunscreen controversies: a critical review |journal=Photodermatology, Photoimmunology & Photomedicine |volume=27 |issue=2| pages=58–67 |doi=10.1111/j.1600-0781.2011.00557.x |pmid=21392107| s2cid=29173997 |doi-access=free}}</ref> and [[Chemistry:Octyl methoxycinnamate|octyl methoxycinnamate]], are [[Chemistry:Organic compound|organic chemical absorbers]] or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as [[Chemistry:Carbon black|carbon black]], [[Chemistry:Titanium dioxide|titanium dioxide]], and [[Chemistry:Zinc oxide|zinc oxide]].

For clothing, the ultraviolet protection factor (UPF) represents the ratio of sunburn-causing UV without and with the protection of the fabric, similar to sun protection factor (SPF) ratings for [[Chemistry:Sunscreen|sunscreen]].{{citation needed|date=July 2020}} Standard summer fabrics have UPFs around 6, which means that about 20% of UV will pass through.{{citation needed|date=July 2020}}

Suspended [[Physics:Nanoparticle|nanoparticle]]s in stained-glass prevent UV rays from causing chemical reactions that change image colors.{{citation needed|date=June 2020}} A set of stained-glass color-reference chips is planned to be used to calibrate the color cameras for the 2019 ESA Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars.{{citation needed|date=May 2020}}

Common [[Engineering:Soda–lime glass|soda–lime glass]], such as window glass, is partially [[Transparency and translucency|transparent]] to UVA, but is [[Physics:Opacity (optics)|opaque]] to shorter wavelengths, passing about 90% of the light above 350&nbsp;nm, but blocking over 90% of the light below 300&nbsp;nm.<ref>{{cite web | title = Soda Lime Glass Transmission Curve | url = http://www.sinclairmfg.com/datasheets/optical3.html | url-status=dead | archive-url = https://web.archive.org/web/20120327213950/http://www.sinclairmfg.com/datasheets/optical3.html | archive-date = 27 March 2012 | access-date = 20 January 2012 }}</ref><ref>{{cite web|url=http://www.pgo-online.com/intl/katalog/curves/B270_kurve.html|title=B270-Superwite Glass Transmission Curve|website=Präzisions Glas & Optik|access-date=2017-01-13|url-status=live|archive-url=https://web.archive.org/web/20170709022735/https://www.pgo-online.com/intl/katalog/curves/B270_kurve.html|archive-date=9 July 2017}}</ref><ref>{{cite web|url=http://www.pgo-online.com/intl/katalog/curves/whitefl_kurve.html|title=Selected Float Glass Transmission Curve|website=Präzisions Glas & Optik|access-date=2017-01-13|url-status=live|archive-url=https://web.archive.org/web/20151019025929/http://www.pgo-online.com/intl/katalog/curves/whitefl_kurve.html|archive-date=19 October 2015}}</ref> A study found that car windows allow 3-4% of ambient UV to pass through, especially if the UV was greater than 380&nbsp;nm.<ref name="UV exposure in cars">{{cite journal |last1=Moehrle |first1=Matthias |last2=Soballa |first2=Martin |last3=Korn |first3=Manfred |title=UV exposure in cars |journal=Photodermatology, Photoimmunology & Photomedicine |date=2003 |volume=19 |issue=4 |pages=175–181 |doi=10.1034/j.1600-0781.2003.00031.x |pmid=12925188 |s2cid=37208948 |language=en |issn=1600-0781}}</ref> Other types of car windows can reduce transmission of UV that is greater than 335&nbsp;nm.<ref name="UV exposure in cars" /> [[Chemistry:Fused quartz|Fused quartz]], depending on quality, can be transparent even to vacuum UV wavelengths. Crystalline [[Chemistry:Quartz|quartz]] and some crystals such as CaF<sub>2</sub> and MgF<sub>2</sub> transmit well down to 150&nbsp;nm or 160&nbsp;nm wavelengths.<ref>{{cite web | url=https://www.newport.com/n/optical-materials | title=Optical Materials | publisher=Newport Corporation | access-date=14 June 2020 | archive-date=11 June 2020 | archive-url=https://web.archive.org/web/20200611014515/https://www.newport.com/n/optical-materials | url-status=live }}</ref>

[[Physics:Wood's glass|Wood's glass]] is a deep violet-blue barium-sodium silicate glass with about 9% nickel oxide developed during [[Social:World War I|World War I]] to block visible light for covert communications. It allows both infrared daylight and ultraviolet night-time communications by being transparent between 320&nbsp;nm and 400&nbsp;nm and also the longer infrared and just-barely-visible red wavelengths. Its maximum UV transmission is at 365&nbsp;nm, one of the wavelengths of mercury lamps.

== Artificial sources ==

=== "Black lights" ===
{{multiple image
|direction = vertical
|width = 220
|image1 = Two black light fluorescent tubes.jpg
|image2 = Two black light lamps.jpg
|footer = Two black light fluorescent tubes, showing use. The longer tube is a F15T8/BLB 18&nbsp;inch, 15&nbsp;watt tube, shown in the bottom image in a standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12&nbsp;inch, 8&nbsp;watt tube, used in a portable battery-powered black light sold as a pet urine detector.
}}
{{Main|Physics:Blacklight}}
A ''black light'' lamp emits long-wave UV‑A radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a [[Physics:Phosphor|phosphor]] on the inner tube surface which emits UV‑A radiation instead of visible light. Some lamps use a deep-bluish-purple [[Physics:Wood's glass|Wood's glass]] optical filter that blocks almost all visible light with wavelengths longer than 400&nbsp;nanometers.<ref>
{{cite web
 |title=Insect-O-Cutor
 |url=http://www.insect-o-cutor.com/ioclibrary/blacklight.pdf
 |url-status=live
 |archive-url=https://web.archive.org/web/20130604215247/http://www.insect-o-cutor.com/ioclibrary/blacklight.pdf
 |archive-date=4 June 2013
}}
</ref> The purple glow given off by these tubes is not the ultraviolet itself, but visible purple light from mercury's 404&nbsp;nm spectral line which escapes being filtered out by the coating. Other black lights use plain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating.

Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light (''see section below''). These are cheaper but very inefficient, emitting only a small fraction of a percent of their power as UV. Mercury-vapor black lights in ratings up to 1&nbsp;kW with UV-emitting phosphor and an envelope of [[Physics:Wood's glass|Wood's glass]] are used for theatrical and concert displays.

Black lights are used in applications in which extraneous visible light must be minimized; mainly to observe ''[[Biology:Fluorescence|fluorescence]]'', the colored glow that many substances give off when exposed to UV light. UV‑A / [[Engineering:UV-B lamps|UV‑B emitting bulbs]] are also sold for other special purposes, such as [[Physics:Tanning lamp|tanning lamp]]s and reptile-husbandry.

===Short-wave ultraviolet lamps===
{{multiple image
| align = right
| direction = vertical
| header =
| image1 = Germicidal Lamp 1.jpg
| caption1 = 9&nbsp;watt germicidal UV bulb, in compact fluorescent (CF) form factor
| image2 = Кварцевая лампа.JPG
| caption2 = Commercial germicidal lamp in butcher shop
| width = 220
}}

Shortwave UV lamps are made using a [[Physics:Fluorescent lamp|fluorescent lamp]] tube with no phosphor coating, composed of [[Chemistry:Fused quartz|fused quartz]] or [[Engineering:Vycor|vycor]], since ordinary glass absorbs UV‑C. These lamps emit ultraviolet light with two peaks in the UV‑C band at 253.7&nbsp;nm and 185&nbsp;nm due to the [[Chemistry:Mercury (element)|mercury]] within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7&nbsp;nm, whereas only 5–10% is at 185&nbsp;nm.<ref>{{cite book |last1=Rodrigues |first1=Sueli |last2=Fernandes |first2=Fabiano Andre Narciso |title=Advances in Fruit Processing Technologies |date=18 May 2012 |publisher=CRC Press |isbn=978-1-4398-5153-1 |page=5 |url=https://books.google.com/books?id=XyXOBQAAQBAJ |language=en |access-date=22 October 2022 |archive-date=5 March 2023 |archive-url=https://web.archive.org/web/20230305221819/https://books.google.com/books?id=XyXOBQAAQBAJ |url-status=live }}</ref> The fused quartz tube passes the 253.7&nbsp;nm radiation but blocks the 185&nbsp;nm wavelength. Such tubes have two or three times the UV‑C power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100&nbsp;watts of electricity consumed by the lamp, they will produce approximately 30–40&nbsp;watts of total UV output. They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.

===Incandescent lamps===
'Black light' incandescent lamps are also made from an incandescent light bulb with a filter coating which absorbs most visible light. [[Engineering:Halogen lamp#Spectrum|Halogen lamps]] with [[Chemistry:Fused quartz|fused quartz]] envelopes are used as inexpensive UV light sources in the near UV range, from 400 to 300&nbsp;nm, in some scientific instruments. Due to its black-body spectrum a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV.

===Gas-discharge lamps===
{{Main|Physics:Gas-discharge lamp}}
Specialized UV [[Physics:Gas-discharge lamp|gas-discharge lamp]]s containing different gases produce UV radiation at particular spectral lines for scientific purposes. [[Chemistry:Argon|Argon]] and [[Physics:Deuterium arc lamp|deuterium arc lamp]]s are often used as stable sources, either windowless or with various windows such as [[Chemistry:Magnesium fluoride|magnesium fluoride]].<ref>
{{cite report
 |last1=Klose    |first1=Jules Z.
 |last2=Bridges  |first2=J. Mervin
 |last3=Ott      |first3=William R.
 |date=June 1987
 |title=Radiometric standards in the V‑UV
 |series=NBS Special Publication
 |id=250–3
 |department=NBS Measurement Services
 |publisher=U.S. [[Organization:National Institute of Standards and Technology|National Institute of Standards and Technology]]
 |url=https://www.nist.gov/calibrations/upload/sp250-3.pdf
 |url-status=live
 |archive-url=https://web.archive.org/web/20160611075213/http://www.nist.gov/calibrations/upload/sp250-3.pdf
 |archive-date=11 June 2016
}}
</ref> These are often the emitting sources in UV spectroscopy equipment for chemical analysis.

Other UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), [[Physics:Deuterium arc lamp|deuterium arc lamp]]s, [[Physics:Xenon arc lamp#Xenon-mercury|mercury-xenon arc lamps]], and [[Physics:Metal-halide lamp|metal-halide arc lamp]]s.

The [[Physics:Excimer lamp|excimer lamp]], a UV source developed in the early 2000s, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet.

===Ultraviolet LEDs===
[[File:UV LED Fluoresence.jpg|thumb|upright|A 380&nbsp;nanometer UV LED makes some common household items fluoresce.]]
Light-emitting diodes (LEDs) can be manufactured to emit radiation in the ultraviolet range. In 2019, following significant advances over the preceding five years, UV‑A LEDs of 365&nbsp;nm and longer wavelength were available, with efficiencies of 50% at 1.0&nbsp;W output. Currently, the most common types of UV LEDs are in 395&nbsp;nm and 365&nbsp;nm wavelengths, both of which are in the UV‑A spectrum. The rated wavelength is the peak wavelength that the LEDs put out, but light at both higher and lower wavelengths are present.

The cheaper and more common 395&nbsp;nm UV LEDs are much closer to the visible spectrum, and give off a purple color. Other UV LEDs deeper into the spectrum do not emit as much visible light<ref>{{cite web
 |title=What is the difference between 365&nbsp;nm and 395&nbsp;nm UV LED lights?
 |website=waveformlighting.com
 |url=https://www.waveformlighting.com/tech/what-is-the-difference-between-365-nm-and-395-nm-uv-led-lights
 |access-date=2020-10-27
 |archive-date=22 May 2021
 |archive-url=https://web.archive.org/web/20210522101632/https://www.waveformlighting.com/tech/what-is-the-difference-between-365-nm-and-395-nm-uv-led-lights
 |url-status=live
 }}</ref> LEDs are used for applications such as [[Physics:UV curing|UV curing]] applications, charging glow-in-the-dark objects such as paintings or toys, and lights for detecting counterfeit money and bodily fluids. UV LEDs are also used in digital print applications and inert UV curing environments. Power densities approaching 3&nbsp;W/cm<sup>2</sup> (30&nbsp;kW/m<sup>2</sup>) are now possible, and this, coupled with recent developments by photo-initiator and resin formulators, makes the expansion of LED cured UV materials likely.

UV‑C LEDs are developing rapidly, but may require testing to verify effective disinfection. Citations for large-area disinfection are for non-LED UV sources<ref>
{{cite journal
 |last1=Boyce |first1=J.M.
 |year=2016
 |title=Modern technologies for improving cleaning and disinfection of environmental surfaces in hospitals
 |journal=Antimicrobial Resistance and Infection Control
 |volume=5 |page=10
 |pmid=27069623 |pmc=4827199 |doi=10.1186/s13756-016-0111-x
|doi-access=free
 }}
</ref> known as [[Physics:Germicidal lamp|germicidal lamp]]s.<ref name="Liverpool, UVGI" >
{{cite web
 |title=Ultraviolet germicidal irradiation  |page=3
 |publisher=[[Organization:University of Liverpool|University of Liverpool]]
 |url=https://www.liverpool.ac.uk/media/livacuk/radiation/pdf/UV_germicidal.pdf
 |url-status=dead
 |archive-url=https://web.archive.org/web/20160806185506/https://www.liverpool.ac.uk/media/livacuk/radiation/pdf/UV_germicidal.pdf
 |archive-date=2016-08-06
}}
</ref> Also, they are used as line sources to replace deuterium lamps in liquid chromatography instruments.<ref>
{{cite news
 |title=UV‑C LEDs Enhance Chromatography Applications
 |website=GEN Eng News
 |url=http://www.genengnews.com/gen-articles/uvc-leds-enhance-chromatography-applications/5880
 |url-status=live
 |archive-url=https://web.archive.org/web/20161104020423/http://www.genengnews.com/gen-articles/uvc-leds-enhance-chromatography-applications/5880
 |archive-date=4 November 2016
}}
</ref>

===Ultraviolet lasers===
[[Engineering:Gas laser|Gas laser]]s, [[Engineering:Laser diode|laser diode]]s, and [[Physics:Solid-state laser|solid-state laser]]s can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1&nbsp;nm and 357.6&nbsp;nm in wavelength. Another type of high-power gas lasers are excimer lasers. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV [[Chemistry:Argon fluoride laser|argon-fluoride]] excimer lasers operating at 193&nbsp;nm are routinely used in [[Engineering:Integrated circuit|integrated circuit]] production by [[Engineering:Photolithography|photolithography]]. The current{{Clarify timeframe|date=June 2020}} wavelength limit of production of coherent UV is about 126&nbsp;nm, characteristic of the Ar<sub>2</sub>* excimer laser.

Direct UV-emitting laser diodes are available at 375&nbsp;nm.<ref>{{cite web
 | title=UV laser diode: 375&nbsp;nm center wavelength
 | website=Thorlabs
 | location=United States / Germany
 | series=Product Catalog
 | language=en
 | url=http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=5400
 | access-date=14 December 2014
 | archive-date=15 December 2014
 | archive-url=https://web.archive.org/web/20141215055051/http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=5400
 | url-status=live
 }}</ref> UV diode-pumped solid state lasers have been demonstrated using [[Chemistry:Cerium|cerium]]-[[Chemistry:Dopant|doped]] lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at [[Organization:Lawrence Livermore National Laboratory|Lawrence Livermore National Laboratory]].<ref name="Marshall1996">
{{cite report
 |last = Marshall |first = Chris
 |title = A simple, reliable ultraviolet laser: The Ce:LiSAF
 |publisher = [[Organization:Lawrence Livermore National Laboratory|Lawrence Livermore National Laboratory]]
 |year = 1996
 |url = https://www.llnl.gov/str/Marshall.html
 |access-date = 2008-01-11  |url-status = dead
 |archive-url = https://web.archive.org/web/20080920155324/https://www.llnl.gov/str/Marshall.html
 |archive-date = 20 September 2008
}}
</ref> Wavelengths shorter than 325&nbsp;nm are commercially generated in [[Physics:Diode-pumped solid-state laser|diode-pumped solid-state laser]]s. Ultraviolet lasers can also be made by applying [[Physics:Nonlinear optics|frequency conversion]] to lower-frequency lasers.

Ultraviolet lasers have applications in industry ([[Physics:Laser engraving|laser engraving]]), medicine (dermatology, and keratectomy), chemistry (MALDI), free-air secure communications, computing ([[Engineering:Optical storage|optical storage]]), and manufacture of integrated circuits.

===Tunable vacuum ultraviolet (VUV)===
The vacuum ultraviolet (V‑UV) band (100–200&nbsp;nm) can be generated by [[Physics:Nonlinear optics|non-linear 4&nbsp;wave mixing]] in gases by sum or difference frequency mixing of 2 or more longer wavelength lasers. The generation is generally done in gasses (e.g. krypton, hydrogen which are two-photon resonant near 193&nbsp;nm)<ref name=straussfunk/> or metal vapors (e.g. magnesium). By making one of the lasers tunable, the V‑UV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the V‑UV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4&nbsp;wave mixing. Difference frequency mixing (i.e., {{nowrap|{{mvar|f}}{{sub|1}} + {{mvar|f}}{{sub|2}} − {{mvar|f}}{{sub|3}}}}) has an advantage over sum frequency mixing because the phase matching can provide greater tuning.<ref name=straussfunk/>

In particular, difference frequency mixing two photons of an {{chem|[[Chemistry:Argon|Ar]]||[[Chemistry:Fluorine|F]]}} (193&nbsp;nm) excimer laser with a tunable visible or near&nbsp;IR laser in hydrogen or krypton provides resonantly enhanced tunable V‑UV covering from 100&nbsp;nm to 200&nbsp;nm.<ref name=straussfunk>
{{cite journal
 | last1 = Strauss  | first1 = C.E.M.
 | last2 = Funk     | first2 = D.J.
 | year = 1991
 | title = Broadly tunable difference-frequency generation of VUV using two-photon resonances in H{{sub|2}} and Kr
 | journal = Optics Letters
 | volume = 16  | issue = 15  | pages = 1192–4
 | doi=10.1364/ol.16.001192  | pmid = 19776917
 | bibcode = 1991OptL...16.1192S
 | url = https://www.osapublishing.org/ol/fulltext.cfm?uri=ol-16-15-1192&id=10705
 | access-date = 2021-04-11
}}
</ref> Practically, the lack of suitable gas / vapor cell window materials above the [[Chemistry:Lithium fluoride|lithium fluoride]] cut-off wavelength limit the tuning range to longer than about 110&nbsp;nm. Tunable V‑UV wavelengths down to 75&nbsp;nm was achieved using window-free configurations.<ref name="O2Ar">
{{Cite journal
 |last1 = Xiong  |first1 = Bo
 |last2 = Chang  |first2 = Yih-Chung
 |last3 = Ng     |first3 = Cheuk-Yiu
 |year = 2017
 |title = Quantum-state-selected integral cross sections for the charge transfer collision of {{math|{{small|O{{su|b=2|p=+}} (a{{sup|4}} Π {{sub|u 5/2,3/2,1/2,−1/2}}:}}}} {{math|{{small|v{{sup|+}}{{=}}1–2; J{{sup|+}})}}}} {{math|{{small|[ O{{su|b=2|p=+}} (X{{sup|2}} Π {{sub|g 3/2,1/2}}:}}}} {{math|{{small|v{{sup|+}}{{=}}22–23; J{{sup|+}}) ] + Ar}}}} at center-of-mass collision energies of 0.05–10.00&nbsp;eV
 |journal = Phys. Chem. Chem. Phys.
 |volume=19 |issue = 43 |pages=29057–29067
 |bibcode= 2017PCCP...1929057X  |pmid = 28920600 |doi = 10.1039/C7CP04886F
 |url = http://pubs.rsc.org/-/content/articlehtml/2017/cp/c7cp04886f
 |url-status = live
 |archive-url = https://web.archive.org/web/20171115202941/http://pubs.rsc.org/-/content/articlehtml/2017/cp/c7cp04886f
 |archive-date = 15 November 2017
}}
</ref>

===Plasma and synchrotron sources of extreme UV===
Lasers have been used to indirectly generate non-coherent extreme&nbsp;UV (E‑UV) radiation at 13.5&nbsp;nm for [[Physics:Extreme ultraviolet lithography|extreme ultraviolet lithography]]. The E‑UV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser.<ref>
{{cite web
 |title=E‑UV nudges toward 10&nbsp;nm
 |website=EE Times
 |url=http://www.eetimes.com/document.asp?doc_id=1322626
 |url-status=dead |access-date=26 September 2014
 |archive-url=https://web.archive.org/web/20141015014640/http://www.eetimes.com/document.asp?doc_id=1322626
 |archive-date=15 October 2014
}}
</ref> This technique does not require a synchrotron, yet can produce UV at the edge of the X‑ray spectrum. [[Engineering:Synchrotron light source|Synchrotron light source]]s can also produce all wavelengths of UV, including those at the boundary of the UV and X‑ray spectra at 10&nbsp;nm.

==Human health-related effects==
{{Further|Chemistry:Health effects of sunlight exposure}}
The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as [[Physics:Fluorescent lamps and health|fluorescent lamps and health]]. Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial.<ref name="sivamani">{{cite journal |last1=Sivamani |first1=R.K. |last2=Crane |first2=L.A. |last3=Dellavalle |first3=R.P. |title=The benefits and risks of ultraviolet tanning and its alternatives: The role of prudent sun exposure |journal=Dermatologic Clinics |date=April 2009 |volume=27 |issue=2 |pages=149–154 |pmid=19254658 |doi=10.1016/j.det.2008.11.008 |pmc=2692214}}</ref>

===Beneficial effects===

UV light (specifically, UV‑B) causes the body to produce [[Chemistry:Vitamin D|vitamin D]],<ref>{{Cite journal |last1=Wacker |first1=Matthias |last2=Holick |first2=Michael F. |date=2013-01-01 |title=Sunlight and Vitamin D |journal=Dermato-endocrinology |volume=5 |issue=1 |pages=51–108 |doi=10.4161/derm.24494 |issn=1938-1972 |pmc=3897598 |pmid=24494042}}</ref> which is essential for life. Humans need some UV radiation to maintain adequate vitamin&nbsp;D levels. According to the World Health Organization:<ref name="who.int"/>
<blockquote>There is no doubt that a little sunlight is good for you! But 5–15&nbsp;minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high.</blockquote>

Vitamin D can also be obtained from food and supplementation.<ref>{{cite journal |last1=Lamberg-Allardt |first1=Christel |title=Vitamin&nbsp;D in foods and as supplements |journal=Progress in Biophysics and Molecular Biology |date=1 September 2006 |volume=92 |issue=1 |pages=33–38 |doi=10.1016/j.pbiomolbio.2006.02.017 |pmid=16618499 |language=en |issn=0079-6107 |doi-access=free }}</ref> Excess sun exposure produces harmful effects, however.<ref name="who.int">{{cite report |url=https://www.who.int/uv/faq/uvhealtfac/en/index1.html |title=The known health effects of UV: Ultraviolet radiation and the INTERSUN Programme |archive-url=https://web.archive.org/web/20161016090300/http://www.who.int/uv/faq/uvhealtfac/en/index1.html |archive-date=16 October 2016 |publisher=World Health Organization}}</ref>

Vitamin D promotes the creation of [[Chemistry:Serotonin|serotonin]]. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives.<ref>{{cite magazine |author=Korb, Alex |date=17 November 2011 |title=Boosting your serotonin activity |magazine=Psychology Today |url=https://www.psychologytoday.com/blog/prefrontal-nudity/201111/boosting-your-serotonin-activity |archive-url=https://archive.today/20170801135657/https://www.psychologytoday.com/blog/prefrontal-nudity/201111/boosting-your-serotonin-activity |archive-date=1 August 2017}}</ref> Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings.<ref>{{cite journal |last = Young |first = S.N. |year = 2007 |title = How to increase serotonin in the human brain without drugs |journal = Journal of Psychiatry and Neuroscience |volume = 32 |issue = 6 |pages = 394–399 |pmid = 18043762 |pmc = 2077351}}</ref>

====Skin conditions====
UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat [[Medicine:Psoriasis|psoriasis]], eczema, [[Medicine:Jaundice|jaundice]], [[Medicine:Vitiligo|vitiligo]], [[Medicine:Atopic dermatitis|atopic dermatitis]], and localized [[Medicine:Scleroderma|scleroderma]].<ref>{{cite journal |last1=Juzeniene |first1=Asta |last2=Moan |first2=Johan |title=Beneficial effects of UV radiation other than via vitamin&nbsp;D production |journal=Dermato-Endocrinology|date=27 October 2014 |volume=4 |issue=2 |pages=109–117 |doi=10.4161/derm.20013 |pmid=22928066 |pmc=3427189}}</ref><ref>[http://healthycanadians.gc.ca/healthy-living-vie-saine/environment-environnement/sun-soleil/effects-uv-effets-eng.php "Health effects of ultraviolet radiation"] {{webarchive|url=https://web.archive.org/web/20161008013441/http://healthycanadians.gc.ca/healthy-living-vie-saine/environment-environnement/sun-soleil/effects-uv-effets-eng.php |date=8 October 2016 }}. Government of Canada.</ref> In addition, UV light, in particular UV‑B radiation, has been shown to induce [[Biology:Cell cycle|cell cycle]] arrest in keratinocytes, the most common type of skin cell.<ref>{{Cite journal |last1=Herzinger |first1=T. |last2=Funk |first2=J.O. |last3=Hillmer |first3=K. |last4=Eick |first4=D. |last5=Wolf |first5=D.A. |last6=Kind |first6=P. |year=1995 |title=Ultraviolet&nbsp;B irradiation-induced G2 cell cycle arrest in human keratinocytes by inhibitory phosphorylation of the cdc2 cell cycle kinase |journal=Oncogene |volume=11 |issue=10 |pages=2151–2156 |pmid=7478536}}</ref> As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary.<ref>{{cite journal |last1=Bhatia |first1=Bhavnit K. |last2=Bahr |first2=Brooks A. |last3=Murase |first3=Jenny E. |year=2015 |title=Excimer laser therapy and narrowband ultraviolet&nbsp;B therapy for exfoliative cheilitis |journal=International Journal of Women's Dermatology |volume=1 |issue=2 |pages=95–98 |doi=10.1016/j.ijwd.2015.01.006 |pmid=28491966 |pmc=5418752}}</ref>

=== Harmful effects ===
[[File:Erythemal action spectrum.svg|thumb|right|Sunburn effect (as measured by the UV index) is the product of the sunlight spectrum (radiation intensity) and the erythemal action spectrum (skin sensitivity) across the range of UV wavelengths. Sunburn production per milliwatt of radiation intensity is increased by nearly a factor of 100 between the near UV‑B wavelengths of 315–295&nbsp;nm.]]

In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and [[Biology:Retina|retina]]. The risk is elevated at high [[Altitude|altitude]]s and people living in high [[Earth:Latitude|latitude]] areas where snow covers the ground right into early summer and sun positions even at [[Zenith|zenith]] are low, are particularly at risk.<ref name="Meyer-Rochow 2000">{{cite journal |last=Meyer-Rochow |first=Victor Benno |year=2000 |title= Risks, especially for the eye, emanating from the rise of solar UV-radiation in the Arctic and Antarctic regions |journal=International Journal of Circumpolar Health |volume=59 |issue=1 |pages=38–51 |pmid=10850006}}</ref> Skin, the circadian system, and the [[Biology:Immune system|immune system]] can also be affected.<ref>{{cite web |title=Health effects of UV radiation |url=https://www.who.int/uv/health/uv_health2/en/ |publisher=World Health Organization |url-status=dead |archive-url=https://web.archive.org/web/20150317041542/http://www.who.int/uv/health/en/ |archive-date=17 March 2015 }}</ref>

The differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum".<ref>{{cite report
 |title=Ultraviolet Radiation Guide
 |date=April 1992
 |publisher=U.S.Navy
 |department=Environmental Health Center
 |place=Norfolk, Virginia
 |url=https://www.med.navy.mil/sites/nmcphc/Documents/policy-and-instruction/ih-ultraviolet-radiation-technical-guide.pdf
 |access-date=21 December 2019
 |archive-date=21 December 2019
 |archive-url=https://web.archive.org/web/20191221165034/https://www.med.navy.mil/sites/nmcphc/Documents/policy-and-instruction/ih-ultraviolet-radiation-technical-guide.pdf
 |url-status=dead
 }}</ref> The action spectrum shows that UVA does not cause immediate reaction, but rather UV begins to cause photokeratitis and skin redness (with lighter skinned individuals being more sensitive) at wavelengths starting near the beginning of the UVB band at 315&nbsp;nm, and rapidly increasing to 300&nbsp;nm. The skin and eyes are most sensitive to damage by UV at 265–275&nbsp;nm, which is in the lower UV‑C band. At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with so little penetrating the atmosphere. The WHO-standard [[Astronomy:Ultraviolet index|ultraviolet index]] is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at a given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UV‑A and UV‑B bands.

==== Skin damage ====
[[File:DNA UV mutation.svg|thumb|right|Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly.]]

Overexposure to UV‑B radiation not only can cause sunburn but also some forms of [[Medicine:Skin cancer|skin cancer]]. However, the degree of redness and eye irritation (which are largely not caused by UV‑A) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet.<ref>{{cite web |title=What is ultraviolet (UV) radiation? |website=cancer.org |url=https://www.cancer.org/cancer/skin-cancer/prevention-and-early-detection/what-is-uv-radiation.html |access-date=2017-06-11 |url-status=live |archive-url=https://web.archive.org/web/20170403181332/https://www.cancer.org/cancer/skin-cancer/prevention-and-early-detection/what-is-uv-radiation.html |archive-date=3 April 2017}}</ref>

All bands of UV radiation damage [[Biology:Collagen|collagen]] fibers and accelerate aging of the skin. Both UV‑A and UV‑B destroy vitamin&nbsp;A in skin, which may cause further damage.<ref>
{{cite journal
 |last1 = Torma      |first1 = H.
 |last2 = Berne      |first2 = B.
 |last3 = Vahlquist  |first3 = A.
 |year=1988
 |title = UV irradiation and topical vitamin A modulate retinol esterification in hairless mouse epidermis
 |journal = Acta Derm. Venereol.
 |volume = 68 |issue = 4 |pages = 291–299
 |pmid = 2459873
}}
</ref>

UVB radiation can cause direct DNA damage.<ref name="autogenerated145">{{cite journal |vauthors=Bernstein C, Bernstein H, Payne CM, Garewal H |date=June 2002 |title=DNA repair / pro-apoptotic dual-role proteins in five major DNA repair pathways: Fail-safe protection against carcinogenesis |journal=Mutat. Res. |volume=511 |issue=2 |pages=145–78 |pmid=12052432 |doi= 10.1016/S1383-5742(02)00009-1}}</ref> This cancer connection is one reason for concern about [[Earth:Ozone depletion|ozone depletion]] and the ozone hole.

The most deadly form of [[Medicine:Skin cancer|skin cancer]], malignant [[Medicine:Melanoma|melanoma]], is mostly caused by DNA damage independent from UV‑A radiation. This can be seen from the absence of a direct UV signature mutation in 92% of all melanoma.<ref name=Davies>{{cite journal |author1=Davies, H. |author2=Bignell, G.R. |author3=Cox, C. |date=June 2002 |title=Mutations of the ''BRAF'' gene in human cancer |journal=Nature |volume=417 |issue=6892 |pages=949–954 |doi=10.1038/nature00766 |pmid=12068308 |url=http://eprints.gla.ac.uk/121/1/Davis%2CH_2002_pdf.pdf |bibcode=2002Natur.417..949D |s2cid=3071547 |s2cid-access=free |access-date=30 November 2019 |archive-date=5 August 2020 |archive-url=https://web.archive.org/web/20200805053025/http://eprints.gla.ac.uk/121/1/Davis%2CH_2002_pdf.pdf |url-status=live }}</ref> Occasional overexposure and sunburn are probably greater risk factors for melanoma than long-term moderate exposure.<ref name=NS>{{cite magazine |first=Richard |last=Weller |date=10 June 2015 |title=Shunning the sun may be killing you in more ways than you think |magazine=New Scientist |url=https://www.newscientist.com/article/mg22630250-500-shunning-the-sun-may-be-killing-you-in-more-ways-than-you-think |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20170609062643/https://www.newscientist.com/article/mg22630250-500-shunning-the-sun-may-be-killing-you-in-more-ways-than-you-think/ |archive-date=9 June 2017}}</ref> UV‑C is the highest-energy, most-dangerous type of ultraviolet radiation, and causes adverse effects that can variously be mutagenic or carcinogenic.<ref>{{cite book |author=Hogan, C. Michael |orig-date=November 12, 2010 |date=May 25, 2012 |article=Sunlight |editor1=Saundry, P. |editor2=Cleveland, C. |title=Encyclopedia of Earth |article-url=http://www.eoearth.org/view/article/160592/ |archive-url=https://web.archive.org/web/20131019060416/http://www.eoearth.org/view/article/160592/ |archive-date=19 October 2013}}</ref>

In the past, UV‑A was considered not harmful or less harmful than UV‑B, but today it is known to contribute to skin cancer via [[Physics:Indirect DNA damage|indirect DNA damage]] (free radicals such as reactive oxygen species).{{citation needed|date=July 2020}} UV‑A can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. The DNA damage caused indirectly to skin by UV‑A consists mostly of single-strand breaks in DNA, while the damage caused by UV‑B includes direct formation of thymine dimers or cytosine dimers and double-strand DNA breakage.<ref>{{cite journal | pmid = 22271212 | doi=10.1007/s00403-012-1212-x | title=DNA damage after acute exposure of mice skin to physiological doses of UVB and UVA light |date=January 2012 | journal=Arch. Dermatol. Res. |vauthors=Svobodová AR, Galandáková A, Sianská J |display-authors=0 | volume=304 | issue=5 | pages=407–412| s2cid=20554266 }}</ref> UV‑A is immunosuppressive for the entire body (accounting for a large part of the immunosuppressive effects of sunlight exposure), and is mutagenic for basal cell keratinocytes in skin.<ref>{{cite journal | pmid = 22123419 | doi=10.1016/j.sder.2011.08.002 | volume=30 | issue=4 | title=Ultraviolet&nbsp;A radiation: Its role in immunosuppression and carcinogenesis |date=December 2011 | journal=Semin. Cutan. Med. Surg. | pages=214–21 |vauthors=Halliday GM, Byrne SN, Damian DL }}</ref>

UVB photons can cause direct DNA damage. UV‑B radiation [[Physics:Excited state|excites]] DNA molecules in skin cells, causing aberrant [[Chemistry:Covalent bond|covalent bond]]s to form between adjacent [[Chemistry:Pyrimidine|pyrimidine]] bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as [[Biology:Nucleotide excision repair|nucleotide excision repair]] that employs about 30&nbsp;different proteins.<ref name="autogenerated145"/> Those pyrimidine dimers that escape this repair process can induce a form of programmed cell death ([[Biology:Apoptosis|apoptosis]]) or can cause DNA replication errors leading to [[Biology:Mutation|mutation]].

As a defense against UV radiation, the amount of the brown pigment [[Chemistry:Melanin|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, protecting the skin against both [[Physics:Direct DNA damage|direct]] and [[Physics:Indirect DNA damage|indirect DNA damage]] from the UV. UV‑A gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the [[Chemistry:Melanin|melanin]] from [[Biology:Melanocyte|melanocyte]]s. UV‑B yields a tan that takes roughly 2&nbsp;days to develop because it stimulates the body to produce more melanin.

====Sunscreen safety debate====
{{Main|Chemistry:Sunscreen}}

[[File:UV and Vis Sunscreen.jpg|thumb|left|Demonstration of the effect of sunscreen. The man's face has sunscreen on his right side only. The left image is a regular photograph of his face; the right image is of reflected UV light. The side of the face with sunscreen is darker because the sunscreen absorbs the UV light.]]

Medical organizations recommend that patients protect themselves from UV radiation by using [[Chemistry:Sunscreen|sunscreen]]. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.<ref name=Parsons>{{cite journal |author1=Xu, C. |author2=Green, Adele |author3=Parisi, Alfio |author4=Parsons, Peter G |year= 2001 |title= Photosensitization of the sunscreen octyl p‑dimethylaminobenzoate&nbsp;b UV‑A in human melanocytes but not in keratinocytes |journal= Photochemistry and Photobiology |volume= 73 |issue= 6 |pages=600–604 |doi=10.1562/0031-8655(2001)073<0600:POTSOP>2.0.CO;2 |pmid=11421064|s2cid=38706861 }}</ref><ref name=Knowland1993>{{cite journal |author1=Knowland, John |author2=McKenzie, Edward A. |author3=McHugh, Peter J. |author4=Cridland, Nigel A. |title= Sunlight-induced mutagenicity of a common sunscreen ingredient | journal= FEBS Letters |volume= 324 |pages=309–313 |year=1993 |pmid=8405372 |doi= 10.1016/0014-5793(93)80141-G | issue=3|s2cid=23853321 }}</ref> The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage.<ref>{{cite journal | last1 = Chatelaine | first1 = E. | last2 = Gabard | first2 = B. | last3 = Surber | first3 = C. | year = 2003 | title = Skin penetration and sun protection factor of five UV filters: Effect of the vehicle | url = http://www.karger.com/Article/FullText/68291 | journal = Skin Pharmacol. Appl. Skin Physiol | volume = 16 | issue = 1 | pages = 28–35 | doi = 10.1159/000068291 | pmid = 12566826 | s2cid = 13458955 | access-date = 26 December 2013 | archive-date = 27 December 2013 | archive-url = https://web.archive.org/web/20131227063745/http://www.karger.com/Article/FullText/68291 | url-status = live }}</ref>

Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UV‑B, and the usual SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UV‑B protection factor".<ref>{{cite journal |pmid=21283919 |volume=10 |issue=2 |title=The impact of natural sunlight exposure on the UV‑B – sun protection factor (UVB-SPF) and UVA protection factor (UVA-PF) of a UV‑A / UV‑B SPF&nbsp;50 sunscreen |date=February 2011 |journal=J. Drugs Dermatol. |pages=150–155 |vauthors=Stephens TJ, Herndon JH, Colón LE, Gottschalk RW }}</ref> This rating, however, offers no data about important protection against UVA,<ref>{{cite journal |pmid=21669263 |doi=10.1016/j.ijpharm.2011.05.071 |volume=415 |issue=1–2 |title=Sunscreen products: what do they protect us from? |date=August 2011 |journal=Int. J. Pharm. |pages=181–184 |vauthors=Couteau C, Couteau O, Alami-El Boury S, Coiffard LJ }}</ref> which does not primarily cause sunburn but is still harmful, since it causes indirect DNA damage and is also considered carcinogenic. Several studies suggest that the absence of UV‑A filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users.<ref name=Garland>{{cite journal |vauthors=Garland C, Garland F, Gorham E |title=Could sunscreens increase melanoma risk? |journal=Am. J. Public Health |volume=82 |issue=4 |pages=614–615 |year=1992 |pmid=1546792 |doi=10.2105/AJPH.82.4.614 |pmc=1694089}}</ref><ref name=Westerdahl2000>{{cite journal |vauthors=Westerdahl J, Ingvar C, Masback A, Olsson H |title= Sunscreen use and malignant melanoma | journal= International Journal of Cancer |volume=87 |issue=1 |pages=145–150 |year=2000 |pmid=10861466 |doi=10.1002/1097-0215(20000701)87:1<145::AID-IJC22>3.0.CO;2-3 |doi-access=free }}</ref><ref name=Autier>{{cite journal |vauthors=Autier P, Dore JF, Schifflers E |title=Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France |journal=Int. J. Cancer |volume=61 |issue= 6|pages=749–755 |year=1995| doi = 10.1002/ijc.2910610602 |pmid=7790106|s2cid=34941555 |display-authors=0}}</ref><ref name="Weinstock">{{cite journal |author=Weinstock |first=M. A. |year=1999 |title=Do sunscreens increase or decrease melanoma risk: An epidemiologic evaluation |url=https://www.jidsponline.org/action/showPdf?pii=S1087-0024%2815%2930243-4 |url-status=live |journal=Journal of Investigative Dermatology Symposium Proceedings |volume=4 |issue=1 |pages=97–100 |doi=<!-- Deny Citation Bot--> |pmid=10537017 |archive-url=https://web.archive.org/web/20221205021844/https://www.jidsponline.org/action/showPdf?pii=S1087-0024(15)30243-4 |archive-date=5 December 2022 |access-date=5 December 2022}}</ref><ref name=Vainio>{{cite journal |author1=Vainio, H. |author2=Bianchini, F. |title=Commentary: Cancer-preventive effects of sunscreens are uncertain |journal= Scandinavian Journal of Work, Environment & Health |volume=26 |issue=6 |pages=529–531 |year=2000 |doi=10.5271/sjweh.578 |doi-access=free}}</ref> Some sunscreen lotions contain [[Chemistry:Titanium dioxide|titanium dioxide]], [[Chemistry:Zinc oxide|zinc oxide]], and [[Chemistry:Avobenzone|avobenzone]], which help protect against UV‑A rays.

The photochemical properties of melanin make it an excellent [[Physics:Photoprotection|photoprotectant]]. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of [[Biology:Reactive oxygen species|reactive oxygen species]] may be increased.<ref name="Hanson">{{cite journal |author1=Hanson, Kerry M. |author2=Gratton, Enrico |author3=Bardeen, Christopher J. |title=Sunscreen enhancement of UV-induced reactive oxygen species in the skin |doi=10.1016/j.freeradbiomed.2006.06.011 |journal=Free Radical Biology and Medicine |volume=41 |issue=8 |pages=1205–1212 |year=2006 |pmid=17015167 |s2cid=13999532 |url=http://www.escholarship.org/uc/item/9f14s2dd |access-date=6 September 2018 |archive-date=6 August 2020 |archive-url=https://web.archive.org/web/20200806013940/https://www.escholarship.org/uc/item/9f14s2dd |url-status=live }}</ref><ref name=Parsons/><ref name=Knowland1993 /><ref name=Damiani1999>{{cite journal |author1=Damiani, E. |author2=Greci, L. |author3=Parsons, R. |author4=Knowland, J. |title=Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient |journal= Free Radic. Biol. Med. |volume=26 |issue=7–8 |pages=809–816 |year=1999 |doi=10.1016/S0891-5849(98)00292-5 |pmid=10232823}}</ref> The amount of sunscreen that penetrates through the [[Biology:Stratum corneum|stratum corneum]] may or may not be large enough to cause damage.

In an experiment by Hanson ''et al''. that was published in 2006, the amount of harmful [[Biology:Reactive oxygen species|reactive oxygen species]] (ROS) was measured in untreated and in sunscreen treated skin. In the first 20&nbsp;minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60&nbsp;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.<ref name="Hanson"/> The study indicates that sunscreen must be reapplied within 2&nbsp;hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.<ref name="Hanson"/>

==== Aggravation of certain skin conditions ====
Ultraviolet radiation can aggravate several skin conditions and diseases, including<ref name=euroderm>{{cite report |title=§2 Photoaggravated disorders |series=European guidelines for photodermatoses |website=European Dermatology Forum |url=http://www.euroderm.org/images/stories/guidelines/guideline_Photoaggravated_dermatoses.pdf |access-date=1 January 2016 }}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> [[Medicine:Systemic lupus erythematosus|systemic lupus erythematosus]], Sjögren's syndrome, Sinear Usher syndrome, [[Medicine:Rosacea|rosacea]], [[Medicine:Dermatomyositis|dermatomyositis]], [[Medicine:Darier's disease|Darier's disease]], Kindler–Weary syndrome and [[Medicine:Porokeratosis|Porokeratosis]].<ref name=Medscape>[https://emedicine.medscape.com/article/1059123-overview#a4 Medscape: Porokeratosis] {{Webarchive|url=https://web.archive.org/web/20210624201419/https://emedicine.medscape.com/article/1059123-overview#a4 |date=24 June 2021 }}.</ref>

====Eye damage====
[[File:UV Warning.jpg|thumb|Signs are often used to warn of the hazard of strong UV sources.]]
The eye is most sensitive to damage by UV in the lower UV‑C band at 265–275&nbsp;nm. Radiation of this wavelength is almost absent from sunlight at the surface of the Earth but is emitted by artificial sources such as the [[Physics:Electric arc|electrical arcs]] employed in [[Physics:Arc welding|arc welding]]. Unprotected exposure to these sources can cause "welder's flash" or "arc eye" (photokeratitis) and can lead to [[Medicine:Cataract|cataract]]s, [[Biology:Pterygium|pterygium]] and pinguecula formation. To a lesser extent, UV‑B in sunlight from 310 to 280&nbsp;nm also causes photokeratitis ("snow blindness"), and the [[Medicine:Cornea|cornea]], the [[Biology:Lens (anatomy)|lens]], and the [[Biology:Retina|retina]] can be damaged.<ref>{{cite report |url=https://www.who.int/uv/faq/uvhealtfac/en/index3.html |title=The known health effects of UV |publisher=World Health Organization |url-status=live |archive-url=https://web.archive.org/web/20161024170159/http://www.who.int/uv/faq/uvhealtfac/en/index3.html |archive-date=24 October 2016}}</ref>

Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light can reach the eyes 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.<ref>{{cite web |url=https://www.who.int/uv/faq/whatisuv/en/index3.html |title=UV radiation |publisher=World Health Organization |url-status=live |archive-url=https://web.archive.org/web/20161025234856/http://www.who.int/uv/faq/whatisuv/en/index3.html |archive-date=25 October 2016}}</ref><ref>{{cite report |title=What is UV radiation and how much does it increase with altitude? |publisher=U.S. National Oceanographic and Atmospheric Administration |url=http://www.wrh.noaa.gov/fgz/science/uv.php?wfo=fgz |url-status=live |archive-url=https://web.archive.org/web/20170103102305/http://www.wrh.noaa.gov/fgz/science/uv.php?wfo=fgz |archive-date=3 January 2017}}</ref>
Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UV‑A and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as [[Physics:Polycarbonate|polycarbonate]], inherently block most UV.<ref>{{cite web |url=https://www.opticianonline.net/features/optical-properties-of-lens-materials-2 |title=Optical properties of lens materials |website=Optician Online |date=6 June 2005 |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20161026000953/https://www.opticianonline.net/features/optical-properties-of-lens-materials-2 |archive-date=26 October 2016}}</ref>

==Degradation of polymers, pigments and dyes==
{{main|Physics:UV degradation}}
[[File:Failedrope1.jpg|thumb|left|UV damaged [[Chemistry:Polypropylene|polypropylene]] rope (left) and new rope (right)]]

[[Physics:UV degradation|UV degradation]] is one form of [[Chemistry:Polymer degradation|polymer degradation]] that affects plastics exposed to [[Astronomy:Sunlight|sunlight]]. The problem appears as discoloration or fading, cracking, loss of strength or disintegration. The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.
[[File:Irspec2.jpg|thumb|upright=1.15|IR spectrum showing carbonyl absorption due to UV degradation of [[Chemistry:Polyethylene|polyethylene]]]]

Sensitive polymers include [[Chemistry:Thermoplastic|thermoplastic]]s and speciality fibers like [[Chemistry:Aramid|aramid]]s. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.

Many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent lamps, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV. Various forms of picture framing glass, including acrylics (plexiglass), laminates, and coatings, offer different degrees of UV (and visible light) protection.

==Applications==
Because of its ability to cause chemical reactions and excite [[Biology:Fluorescence|fluorescence]] in materials, ultraviolet radiation has a number of applications. The following table<ref>{{cite web |title=Classification of UV |website=SETi |url=http://www.s-et.com/en/technology/uvled/ |access-date=2019-12-01 |archive-date=1 December 2019 |archive-url=https://web.archive.org/web/20191201143257/http://www.s-et.com/en/technology/uvled/ |url-status=live }}<br />{{cite web|url=http://www.s-et.com/applications/wavelength.html|title=Applications|website=SETi|access-date=2009-09-26|url-status=usurped|archive-url=https://web.archive.org/web/20080820022822/http://www.s-et.com/applications/wavelength.html|archive-date=20 August 2008}}</ref> gives some uses of specific wavelength bands in the UV spectrum.
* ''13.5&nbsp;nm'': [[Physics:Extreme ultraviolet lithography|Extreme ultraviolet lithography]]
* ''30–200&nbsp;nm'': [[Physics:Photoionization|Photoionization]], [[Physics:Ultraviolet photoelectron spectroscopy|ultraviolet photoelectron spectroscopy]], standard [[Engineering:Integrated circuit|integrated circuit]] manufacture by [[Engineering:Photolithography|photolithography]]
* ''230–365&nbsp;nm'': UV-ID, label tracking, [[Barcode|barcode]]s
* ''230–400&nbsp;nm'': Optical [[Engineering:Sensor|sensor]]s, various instrumentation
* ''240–280&nbsp;nm'': Disinfection, decontamination of surfaces and water ([[Biology:DNA|DNA]] absorption has a peak at 260&nbsp;nm), [[Physics:Germicidal lamp|germicidal lamp]]s<ref name="Liverpool, UVGI" />
* ''200–400&nbsp;nm'': Forensic analysis, drug detection
* ''270–360&nbsp;nm'': [[Biology:Protein|Protein]] analysis, [[Biology:DNA sequencing|DNA sequencing]], [[Medicine:Drug discovery|drug discovery]]
* ''280–400&nbsp;nm'': [[Medicine:Medical imaging|Medical imaging]] of [[Biology:Cell|cells]]
* ''300–320&nbsp;nm'': Light therapy in medicine
* ''300–365&nbsp;nm'': [[Chemistry:Curing|Curing]] of [[Chemistry:Polymer|polymer]]s and printer inks
* ''350–370&nbsp;nm'': [[Engineering:Bug zapper|Bug zapper]]s (flies are most attracted to light at 365&nbsp;nm)<ref>{{cite web |url=http://www.pestproducts.com/uv_light.htm |title=Ultraviolet Light, UV Rays, What is Ultraviolet, UV Light Bulbs, Fly Trap |publisher=Pestproducts.com |access-date=2011-11-08 |url-status=live |archive-url=https://web.archive.org/web/20111008084125/http://www.pestproducts.com/uv_light.htm |archive-date=8 October 2011 }}</ref>

===Photography===
[[File:UV Portrait.jpg|thumb|upright|A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers]]
Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350&nbsp;nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Photography with wavelengths shorter than 350&nbsp;nm requires special quartz lenses which do not absorb the radiation.
[[Engineering:Image sensor|Digital cameras sensors]] may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.

Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in applications as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings. Photography of the fluorescence produced by ultraviolet illumination uses visible wavelengths of light.

[[File:Jupiter.Aurora.HST.UV.jpg|thumb|right|Aurora at [[Astronomy:Jupiter|Jupiter]]'s north pole as seen in ultraviolet light by the Hubble Space Telescope]]
In [[Astronomy:Ultraviolet astronomy|ultraviolet astronomy]], measurements are used to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space.

===Electrical and electronics industry===
[[Physics:Corona discharge|Corona discharge]] on electrical apparatus can be detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of [[Chemistry:Ozone|ozone]] and [[Chemistry:Nitrogen oxide|nitrogen oxide]].<ref>
{{cite magazine
 | title = The daytime UV inspection magazine
 | magazine = Corona
 | url = http://www.seeing-corona.com/
 | url-status=live
 | archive-url = https://web.archive.org/web/20040801222232/http://seeing-corona.com/
 | archive-date = 1 August 2004
}}
</ref>

[[Engineering:EPROM|EPROM]]s (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent ([[Chemistry:Quartz|quartz]]) window on the top of the chip that allows the UV radiation in.

===Fluorescent dye uses===
Colorless [[Physics:Fluorophore|fluorescent dyes]] that emit blue light under UV are added as [[Physics:Optical brightener|optical brightener]]s to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be present and causes the colors and whites to appear whiter or more brightly colored.

UV fluorescent dyes that glow in the primary colors are used in paints, papers, and textiles either to enhance color under daylight illumination or to provide special effects when lit with UV lamps. [[Chemistry:Blacklight paint|Blacklight paint]]s that contain dyes that glow under UV are used in a number of art and aesthetic applications.

Amusement parks often use UV lighting to fluoresce ride artwork and backdrops. This often has the side effect of causing rider's white clothing to glow light-purple.

[[File:RBC Visa UV.jpg|right|thumb|A bird appears on many Visa credit cards when they are held under a UV light source.]]
To help prevent counterfeiting of currency, or forgery of important documents such as driver's licenses and passports, the paper may include a UV watermark or fluorescent multicolor fibers that are visible under ultraviolet light. Postage stamps are tagged with a phosphor that glows under UV rays to permit automatic detection of the stamp and facing of the letter.

UV fluorescent dyes are used in many applications (for example, [[Biology:Biochemistry|biochemistry]] and [[Physics:Forensic science|forensics]]). Some brands of [[Chemistry:Pepper spray|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 the attacker later.

In some types of [[Engineering:Nondestructive testing|nondestructive testing]] UV stimulates fluorescent dyes to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (liquid penetrant inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic particle inspection).

===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.<ref>
{{cite journal
 |last1=Springer |first1=E.       |last2=Almog     |first2=J.
 |last3=Frank    |first3=A.       |last4=Ziv       |first4=Z.
 |last5=Bergman  |first5=P.       |last6=Gui Quang |first6=W.
 |year=1994
 |title=Detection of dry bodily fluids by inherent short wavelength UV luminescence: Preliminary results
 |journal=Forensic Sci. Int.
 |volume=66 |issue=2 |pages=89–94
 |doi=10.1016/0379-0738(94)90332-8 |pmid=8063277
}}
</ref> For example, ejaculated fluids or saliva can be detected by high-power UV sources, irrespective of the structure or colour of the surface the fluid is deposited upon.<ref>
{{cite web
 |author1=Fiedler, Anja
 |author2=Benecke, Mark
 |display-authors=0
 |title=Detection of semen (human and boar) and saliva on fabrics by a very high-powered UV- / VIS-light source
 |website=Bentham Science
 |url=http://www.benthamscience.com/open/toforsj/articles/V001/12TOFORSJ.pdf
 |access-date=2009-12-10 |url-status=dead
 |archive-url=https://web.archive.org/web/20121130113644/http://www.benthamscience.com/open/toforsj/articles/V001/12TOFORSJ.pdf
 |archive-date=30 November 2012
}}
</ref> UV–vis microspectroscopy is also used to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.

Other applications include the authentication of various collectibles and art, and detecting counterfeit currency. Even materials not specially marked with UV sensitive dyes may have distinctive fluorescence under UV exposure or may fluoresce differently under short-wave versus long-wave ultraviolet.

==== Enhancing contrast of ink ====
Using multi-spectral imaging it is possible to read illegible [[Engineering:Papyrus|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.<ref>
{{cite web
 |title=Digital photography of documents
 |publisher=wells-genealogy.org.uk
 |url=http://www.wells-genealogy.org.uk/photography.htm
 |url-status=dead
 |archive-url=https://archive.today/20120919133157/http://www.wells-genealogy.org.uk/photography.htm
 |archive-date=2012-09-19
}}
</ref>

==== Sanitary compliance ====
[[File:Ultra-violet screening for potentially Ebola-carrying liquids (15811190376).jpg|alt=A person wearing full protective gear, glowing in ultraviolet light|thumb|After a training exercise involving fake body fluids, a healthcare worker's personal protective equipment is checked with ultraviolet to find invisible drops of fluids. These fluids could contain deadly viruses or other contamination.]]
Ultraviolet helps detect organic material deposits that remain on surfaces where periodic cleaning and sanitizing may have failed. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected.<ref>
{{cite web
 |title=Defining "What is clean?"
 |series=Integrated cleaning and measurement
 |publisher=Healthy Facilities Institute
 |url=http://www.healthyfacilitiesinstitute.com/a_353-Defining_What_is_Clean
 |language=en |url-status=dead |access-date=24 June 2017
 |archive-url=https://web.archive.org/web/20170921171252/http://www.healthyfacilitiesinstitute.com/a_353-Defining_What_is_Clean
 |archive-date=21 September 2017
}}
</ref><ref>{{cite news
 |title=Non-destructive inspection: Seeing through the B‑52
 |publisher={{wipe|U.S. Air Force}}
 |website=afgsc.af.mil
 |url=http://www.afgsc.af.mil/News/Article-Display/Article/989575/non-destructive-inspection-seeing-through-the-b-52/
 |access-date=24 June 2017
 |archive-date=16 November 2017
 |archive-url=https://web.archive.org/web/20171116031617/http://www.afgsc.af.mil/News/Article-Display/Article/989575/non-destructive-inspection-seeing-through-the-b-52/
 |url-status=live
 }}</ref><ref>
{{cite magazine
 |last1=Escobar  |first1=David
 |date=20 April 2015
 |title=Oxygen cleaning: A validated process is critical for safety
 |magazine=Valve Magazine
 |url=http://www.valvemagazine.com/web-only/categories/technical-topics/6658-oxygen-cleaning-a-validated-process-is-critical-for-safety.html
 |lang=en-gb  |url-status=live
 |archive-url=https://web.archive.org/web/20171115202939/http://www.valvemagazine.com/web-only/categories/technical-topics/6658-oxygen-cleaning-a-validated-process-is-critical-for-safety.html
 |archive-date=15 November 2017
}}
</ref><ref>
{{cite book
 |last1=Raj          |first1=Baldev
 |last2=Jayakumar    |first2=T.
 |last3=Thavasimuthu |first3=M.
 |date=2002
 |title=Practical Non-destructive Testing
 |page=10  |language=en-gb
 |publisher=Woodhead Publishing
 |isbn=9781855736009
 |url=https://books.google.com/books?id=qXcCKsL2IMUC&pg=PA10
}}
</ref>

Perennial news features for many television news organizations involve an investigative reporter using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.<ref>
{{cite magazine
 |title=New investigation finds some hotels don't wash sheets between guests
 |date=15 September 2016
 |magazine=House Beautiful
 |url=http://www.housebeautiful.com/lifestyle/news/a7060/clean-hotel-bed-sheets/
 |language=en |url-status=live
 |archive-url=https://web.archive.org/web/20170703053642/http://www.housebeautiful.com/lifestyle/news/a7060/clean-hotel-bed-sheets/
 |archive-date=3 July 2017
}}
</ref><ref>
{{cite news
 |title=What's hiding in your hotel room?
 |date=17 November 2010
 |website=ABC News
 |url=https://abcnews.go.com/GMA/Health/hiding-hotel-room/story?id=1507794
 |url-status=live
 |archive-url=https://web.archive.org/web/20160722060221/https://abcnews.go.com/GMA/Health/hiding-hotel-room/story?id=1507794
 |archive-date=22 July 2016
}}
</ref>

==== Chemistry ====
UV/Vis spectroscopy is widely used as a technique in [[Chemistry:Chemistry|chemistry]] to analyze [[Chemistry:Chemical structure|chemical structure]], the most notable one being [[Chemistry:Conjugated system|conjugated system]]s. UV radiation is often used to excite a given sample where the fluorescent emission is measured with a [[Physics:Spectrofluorometer|spectrofluorometer]]. In biological research, UV radiation is used for quantification of nucleic acids or [[Biology:Protein|protein]]s. In environmental chemistry, UV radiation could also be used to detect [[Earth:Contaminants of emerging concern|Contaminants of emerging concern]] in water samples.<ref name="ReferenceA" />

In pollution control applications, ultraviolet analyzers are used to detect emissions of nitrogen oxides, sulfur compounds, mercury, and ammonia, for example in the flue gas of fossil-fired power plants.<ref>
{{cite book
 |editor-first=N.E. |editor-last=Battikha
 |year=2007
 |title=The Condensed Handbook of Measurement and Control
 |edition=3rd |pages=65–66
 |publisher=ISA
 |isbn=978-1-55617-995-2
}}
</ref> Ultraviolet radiation can detect thin sheens of [[Earth:Oil spill|spilled oil]] on water, either by the high reflectivity of oil films at UV wavelengths, fluorescence of compounds in oil, or by absorbing of UV created by [[Physics:Raman scattering|Raman scattering]] in water.<ref>
{{cite book
 |editor-first=Mervin |editor-last=Fingas
 |year=2011 |title=Oil Spill Science and Technology
 |pages=123–124
 |publisher=Elsevier
 |isbn=978-1-85617-943-0
}}</ref> UV absorbance can also be uesd to quantify contaminants in wastewater. Most commonly used 254&nbsp;nm UV absorbance is genrally used as a surrogate parameters to quantify NOM.<ref name="ReferenceA">{{Cite journal |last1=Lee |first1=Brandon Chuan Yee |last2=Lim |first2=Fang Yee |last3=Loh |first3=Wei Hao |last4=Ong |first4=Say Leong |last5=Hu |first5=Jiangyong |date=January 2021 |title=Emerging Contaminants: An Overview of Recent Trends for Their Treatment and Management Using Light-Driven Processes |journal=Water |language=en |volume=13 |issue=17 |pages=2340 |doi=10.3390/w13172340 |issn=2073-4441 |doi-access=free }}</ref> Another form of light-based detection method uses a wide spectrum of excitation emission matrix (EEM) to detect and identify contaminants based on their flourense properties.<ref name="ReferenceA"/><ref>{{Cite web |title=What is an Excitation Emission Matrix (EEM)? |url=https://www.horiba.com/int/scientific/technologies/fluorescence-spectroscopy/what-is-an-excitation-emission-matrix-eem/ |access-date=2023-07-10 |website=www.horiba.com |language=en}}</ref> EEM could be used to discriminate different groups of NOM based on the difference in light emission and excitation of fluorophores. NOMs with certain molecular structures are reported to have fluorescent properties in a wide range of excitation/emission wavelengths.<ref>{{Cite journal |last1=Sierra |first1=M.M.D. |last2=Giovanela |first2=M. |last3=Parlanti |first3=E. |last4=Soriano-Sierra |first4=E.J. |date=February 2005 |title=Fluorescence fingerprint of fulvic and humic acids from varied origins as viewed by single-scan and excitation/emission matrix techniques |url=http://dx.doi.org/10.1016/j.chemosphere.2004.09.038 |journal=Chemosphere |volume=58 |issue=6 |pages=715–733 |doi=10.1016/j.chemosphere.2004.09.038 |pmid=15621185 |bibcode=2005Chmsp..58..715S |issn=0045-6535}}</ref><ref name="ReferenceA"/>

[[File:Fluorescent minerals hg.jpg|thumb|right|A collection of mineral samples fluorescing brilliantly at various wavelengths as seen while being irradiated by UV]]
Ultraviolet lamps are also used as part of the analysis of some [[Earth:Mineral|mineral]]s and [[Earth:Gemstone|gems]].

===Material science uses===

====Fire detection====
In general, ultraviolet detectors use either a solid-state device, such as one based on [[Chemistry:Silicon carbide|silicon carbide]] or [[Chemistry:Aluminium nitride|aluminium nitride]], or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by [[Astronomy:Sunlight|sunlight]] and artificial light. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the [[Physics:Infrared|IR]] region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some [[Physics:Thermal radiation|radiation]] in the UVC band, whereas the [[Astronomy:Sun|Sun]]'s radiation at this band is absorbed by the 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 [[Chemistry:Hydrocarbon|hydrocarbon]]s, metals, [[Chemistry:Sulfur|sulfur]], [[Chemistry:Hydrogen|hydrogen]], [[Chemistry:Hydrazine|hydrazine]], and [[Chemistry:Ammonia|ammonia]]. [[Physics:Arc welding|Arc welding]], electrical arcs, [[Astronomy:Lightning|lightning]], [[Physics:X-ray|X-ray]]s 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.

==== Photolithography ====
Ultraviolet radiation is used for very fine resolution [[Engineering:Photolithography|photolithography]], a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The exposure causes chemical reactions to occur in the photoresist. After removal of unwanted 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 is used in the manufacture of [[Physics:Semiconductor|semiconductor]]s, [[Engineering:Integrated circuit|integrated circuit]] components,<ref>{{cite web | title = Deep UV Photoresists | url = http://www.almaden.ibm.com/st/chemistry/lithography/deep_uv/ | archive-url = https://web.archive.org/web/20060312012823/http://www.almaden.ibm.com/st/chemistry/lithography/deep_uv/ | archive-date = 2006-03-12}}</ref> and [[Engineering:Printed circuit board|printed circuit board]]s. Photolithography processes used to fabricate electronic integrated circuits presently use 193&nbsp;nm UV and are experimentally using 13.5&nbsp;nm UV for [[Physics:Extreme ultraviolet lithography|extreme ultraviolet lithography]].

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

[[File:UV effect on finished wood.jpg|thumb|Effects of UV on finished surfaces in 0, 20 and 43 hours]]
Certain inks, coatings, and [[Chemistry:Adhesive|adhesive]]s are formulated with photoinitiators and resins. When exposed to UV light, [[Chemistry:Polymerization|polymerization]] occurs, and so the adhesives harden or cure, usually within a few seconds. Applications include glass and plastic bonding, [[Engineering:Optical fiber|optical fiber]] coatings, the coating of flooring, [[Engineering:UV coating|UV coating]] and paper finishes in offset printing, dental fillings, and decorative fingernail "gels".

UV sources for UV curing applications include UV lamps, UV [[Engineering:LED|LED]]s, and [[Physics:Excimer|excimer]] flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure [[Chemistry:Mercury (element)|Hg]] (mercury) or [[Chemistry:Iron|Fe]] (iron, doped)-based bulbs are used, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs can be used for static applications. Small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.

The impact of UV on polymers is used for modification of the ([[Physics:Surface roughness|roughness]] and hydrophobicity) of polymer surfaces. For example, a [[Chemistry:Poly(methyl methacrylate)|poly(methyl methacrylate)]] surface can be smoothed by vacuum ultraviolet.<ref>{{cite journal|author1=R. V. Lapshin|author2=A. P. Alekhin|author3=A. G. Kirilenko|author4=S. L. Odintsov|author5=V. A. Krotkov|year=2010|title=Vacuum ultraviolet smoothing of nanometer-scale asperities of poly(methyl methacrylate) surface|journal=Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques|volume=4|issue=1|pages=1–11|issn=1027-4510|doi=10.1134/S1027451010010015|s2cid=97385151|url=http://www.lapshin.fast-page.org/publications.htm#vacuum2010|url-status=live|archive-url=https://web.archive.org/web/20130909230837/http://www.lapshin.fast-page.org/publications.htm#vacuum2010|archive-date=9 September 2013}}</ref>

UV radiation is useful in preparing low-surface-energy [[Chemistry:Polymer|polymer]]s for adhesives. Polymers exposed to UV will oxidize, thus raising the [[Physics: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.

===Biology-related uses===

====Air purification====
Using a [[Physics:Photocatalysis|catalytic chemical reaction]] from [[Chemistry:Titanium dioxide|titanium dioxide]] and UVC exposure, oxidation of organic matter converts pathogens, pollens, and mold spores into harmless inert byproducts. However, the reaction of titanium dioxide and UVC is not a straight path. Several hundreds of reactions occur prior to the inert byproducts stage and can hinder the resulting reaction creating formaldehyde, aldehyde, and other VOC's en route to a final stage. Thus, the use of titanium dioxide and UVC requires very specific parameters for a successful outcome. The cleansing mechanism of UV is a photochemical process. Contaminants in the indoor environment are almost entirely organic carbon-based compounds, which break down when exposed to high-intensity UV at 240 to 280&nbsp;nm. Short-wave ultraviolet radiation can destroy DNA in living microorganisms.<ref>{{Cite news|url=https://bestledgrowlightsinfo.com/the-importance-of-uv-light-for-plants-cultivated-indoors/|title=The Importance of UV Light for Plants Cultivated Indoors|date=2017-06-11|work=Best LED Grow Lights Info|access-date=2017-06-24|language=en-US|archive-date=30 July 2018|archive-url=https://web.archive.org/web/20180730203142/https://bestledgrowlightsinfo.com/the-importance-of-uv-light-for-plants-cultivated-indoors/|url-status=live}}</ref> UVC's effectiveness is directly related to intensity and exposure time.

UV has also been shown to reduce gaseous contaminants such as [[Chemistry:Carbon monoxide|carbon monoxide]] and [[Earth:Volatile organic compound|VOCs]].<ref>{{cite journal |last1=Scott|first1=K.J. |last2=Wills|first2=R.R.H. |last3=Patterson|first3=B.D. |year=1971 |journal=Journal of the Science of Food and Agriculture |doi=10.1002/jsfa.2740220916 |title= Removal by ultra-violet lamp of ethylene and other hydrocarbons produced by bananas |volume=22|pages=496–7|issue=9|bibcode=1971JSFA...22..496S }}</ref><ref>{{cite journal |last1=Scott|first1=KJ |last2=Wills|first2=RBH |title=Atmospheric pollutants destroyed in an ultra violet scrubber |year=1973 |journal=Laboratory Practice|volume=22 |issue=2|pages=103–6 |pmid=4688707}}</ref><ref>{{cite journal |last1=Shorter|first1=AJ |last2=Scott|first2=KJ |year=1986|title=Removal of ethylene from air and low oxygen atmospheres with ultra violet radiation|journal=Lebensm-Wiss U Technology |volume=19|pages=176–9}}</ref> UV lamps radiating at 184 and 254&nbsp;nm can remove low concentrations of hydrocarbons and [[Chemistry:Carbon monoxide|carbon monoxide]] if the air is recycled between the room and the lamp chamber. This arrangement prevents the introduction of ozone into the treated air. Likewise, air may be treated by passing by a single UV source operating at 184&nbsp;nm and passed over iron pentaoxide to remove the ozone produced by the UV lamp.

====Sterilization and disinfection====
{{Main|Physics:Ultraviolet germicidal irradiation|Physics:Germicidal lamp}}

[[File:UV-ontsmetting laminaire-vloeikast.JPG|thumb|right|A low-pressure mercury vapor discharge tube floods the inside of a [[Organization:Fume hood|hood]] with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.]]

Ultraviolet lamps are used to [[Biology:Sterilization (microbiology)|sterilize]] workspaces and tools used in biology laboratories and medical facilities. Commercially available low-pressure mercury-vapor lamps emit about 86% of their radiation at 254 nanometers (nm), with 265&nbsp;nm being the peak germicidal effectiveness curve. UV at these germicidal wavelengths damage a microorganism's DNA/RNA so that it cannot reproduce, making it harmless, (even though the organism may not be killed).<ref>{{cite news |last1=Chang |first1=Kenneth |title=Scientists Consider Indoor Ultraviolet Light to Zap Coronavirus in the Air |url=https://www.nytimes.com/2020/05/07/science/ultraviolet-light-coronavirus.html |archive-url=https://web.archive.org/web/20200507214905/https://www.nytimes.com/2020/05/07/science/ultraviolet-light-coronavirus.html |archive-date=2020-05-07 |url-access=subscription |url-status=live |website=The New York Times |date=7 May 2020 |access-date=9 May 2020}}</ref> Since microorganisms can be shielded from ultraviolet rays in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.

UV-C LEDs are relatively new to the commercial market and are gaining in popularity.{{Failed verification|date=April 2020}}<ref>{{cite journal|author1=Welch, David |display-authors=et al |title=Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases|journal=Scientific Reports|volume=8|issue=1|pages=2752|doi=10.1038/s41598-018-21058-w|pmid=29426899|pmc=5807439|issn=2045-2322|date=January 2018|bibcode=2018NatSR...8.2752W}}</ref> Due to their monochromatic nature (±5&nbsp;nm){{Failed verification|date=April 2020}} these LEDs can target a specific wavelength needed for disinfection. This is especially important knowing that pathogens vary in their sensitivity to specific UV wavelengths. LEDs are mercury free, instant on/off, and have unlimited cycling throughout the day.<ref>{{cite web|url=https://www.wateronline.com/doc/coming-of-age-uv-c-led-technology-update-0001|title=Coming of Age UV-C LED Technology Update|website=wateronline.com|url-status=live|archive-url=https://web.archive.org/web/20170420045809/https://www.wateronline.com/doc/coming-of-age-uv-c-led-technology-update-0001|archive-date=20 April 2017}}</ref>

Disinfection using UV radiation is commonly used in [[Earth:Wastewater|wastewater]] treatment applications and is finding an increased usage in municipal drinking [[Earth:Water treatment|water treatment]]. Many bottlers of spring water use UV disinfection equipment to sterilize their water. [[Chemistry:Solar water disinfection|Solar water disinfection]]<ref>{{cite web |url=http://www.sodis.ch/index_EN |title=Solar Water Disinfection |publisher=Sodis.ch |date=2 April 2011 |access-date=2011-11-08 |url-status=dead |archive-url=https://web.archive.org/web/20120831050355/http://www.sodis.ch/index_EN |archive-date=31 August 2012 }}</ref> has been researched for cheaply treating contaminated water using natural [[Astronomy:Sunlight|sunlight]]. The UV-A irradiation and increased water temperature kill organisms in the water.

Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV can be used to [[Chemistry:Pasteurization|pasteurize]] fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV [[Physics:Absorbance|absorbance]] of the juice.

Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 nm. Pulsed light works with xenon flash lamps that can produce flashes several times per second. Disinfection robots use pulsed UV.<ref>{{cite web|url=http://www.xenex.com/xenex-robot/|title=Video Demos|url-status=dead|archive-url=https://web.archive.org/web/20141219140317/http://www.xenex.com/xenex-robot/|archive-date=19 December 2014|access-date=27 November 2014}}</ref>

The antimicrobial effectiveness of filtered far-UVC (222 nm) light on a range of pathogens, including bacteria and fungi showed inhibition of pathogen growth, and since it has lesser harmful effects, it provides essential insights for reliable disinfection in healthcare settings, such as hospitals and long-term care homes.<ref>{{Cite journal |last1=Lorenzo-Leal |first1=Ana C. |last2=Tam |first2=Wenxi |last3=Kheyrandish |first3=Ata |last4=Mohseni |first4=Madjid |last5=Bach |first5=Horacio |date=2023-10-31 |editor-last=Barbosa |editor-first=Joana |title=Antimicrobial Activity of Filtered Far-UVC Light (222 nm) against Different Pathogens |journal=BioMed Research International |language=en |volume=2023 |pages=1–8 |doi=10.1155/2023/2085140 |issn=2314-6141 |pmc=10630020 |pmid=37942030 |doi-access=free }}</ref> UVC has also been shown to be effective at degrading SARS-CoV-2 virus.<ref>{{cite journal | url=https://pubs.acs.org/doi/10.1021/acsphotonics.3c00828 | doi=10.1021/acsphotonics.3c00828 | title=Mechanisms of SARS-CoV-2 Inactivation Using UVC Laser Radiation | date=2023 | last1=Devitt | first1=George | last2=Johnson | first2=Peter B. | last3=Hanrahan | first3=Niall | last4=Lane | first4=Simon I. R. | last5=Vidale | first5=Magdalena C. | last6=Sheth | first6=Bhavwanti | last7=Allen | first7=Joel D. | last8=Humbert | first8=Maria V. | last9=Spalluto | first9=Cosma M. | last10=Hervé | first10=Rodolphe C. | last11=Staples | first11=Karl | last12=West | first12=Jonathan J. | last13=Forster | first13=Robert | last14=Divecha | first14=Nullin | last15=McCormick | first15=Christopher J. | last16=Crispin | first16=Max | last17=Hempler | first17=Nils | last18=Malcolm | first18=Graeme P. A. | last19=Mahajan | first19=Sumeet | journal=ACS Photonics | pmc=10797618 }}</ref>

====Biological====
Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet wavelengths. 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, are 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. For example, in the ''[[Biology:Colias eurytheme|Colias eurytheme]]'' butterfly, males rely on visual cues to locate and identify females. Instead of using chemical stimuli to find mates, males are attracted to the ultraviolet-reflecting color of female hind wings.<ref>{{cite journal | last1 = Silberglied | first1 = Robert E. | last2 = Taylor | first2 = Orley R. | year = 1978 | title = Ultraviolet Reflection and Its Behavioral Role in the Courtship of the Sulfur Butterflies Colias eurytheme and C. philodice (Lepidoptera, Pieridae) | journal = Behavioral Ecology and Sociobiology | volume = 3 | issue = 3| pages = 203–43 | doi=10.1007/bf00296311| s2cid = 38043008 }}</ref> In ''[[Biology:Pieris napi|Pieris napi]]'' butterflies it was shown that females in northern Finland with less UV-radiation present in the environment possessed stronger UV signals to attract their males than those occurring further south. This suggested that it was evolutionarily more difficult to increase the UV-sensitivity of the eyes of the males than to increase the UV-signals emitted by the females.<ref name= "Meyer-Rohow & Järvilehto 1997">{{cite journal| last1=Meyer-Rochow|first1=V.B.|last2=Järvilehto|first2=M.|title=Ultraviolet colours in Pieris napi from northern and southern Finland: Arctic females are the brightest!| journal= Naturwissenschaften|date=1997|volume=84|issue=4|pages= 165–168|bibcode=1997NW.....84..165M|doi=10.1007/s001140050373|s2cid=46142866}}</ref>

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.
[[File:ultraviolet trap entomologist.jpg|thumb|right|Entomologist using a UV lamp for collecting beetles in Chaco, Paraguay]]

The [[Biology:Green fluorescent protein|green fluorescent protein]] (GFP) is often used in [[Biology:Genetics|genetics]] as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.

Ultraviolet traps called [[Engineering:Bug zapper|bug zapper]]s are used to eliminate various small flying insects. They are attracted to the UV and are killed using an electric shock, or trapped once they come into contact with the device. Different designs of ultraviolet radiation traps are also used by entomologists for [[Social:Collecting|collecting]] nocturnal insects during [[Earth:Fauna|faunistic]] survey studies.

====Therapy====
Ultraviolet radiation is helpful in the treatment of skin conditions such as [[Medicine:Psoriasis|psoriasis]] and [[Medicine:Vitiligo|vitiligo]]. Exposure to UVA, while the skin is hyper-photosensitive, by taking [[Chemistry:Psoralen|psoralen]]s is an effective treatment for [[Medicine:Psoriasis|psoriasis]]. Due to the potential of psoralens to cause damage to the [[Biology:Liver|liver]], [[Physics:PUVA therapy|PUVA therapy]] may be used only a limited number of times over a patient's lifetime.

UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the exposure is needed. However, phototherapy can be effective when used in conjunction with certain topical treatments such as anthralin, coal tar, and [[Chemistry:Vitamin A|vitamin A]] and D derivatives, or systemic treatments such as [[Chemistry:Methotrexate|methotrexate]] and [[Chemistry:Acitretin|Soriatane]].<ref>
{{cite web |title = UVB Phototherapy |url = http://www.psoriasis.org/treatment/psoriasis/phototherapy/uvb.php |archive-url=https://web.archive.org/web/20070622180124/http://www.psoriasis.org/treatment/psoriasis/phototherapy/uvb.php |archive-date=22 June 2007 |format=php |access-date=2007-09-23 |publisher=National Psoriasis Foundation, USA}}</ref>

====Herpetology====
[[Biology:Reptile|Reptile]]s need UVB for biosynthesis of vitamin D, and other metabolic processes.<ref>{{Cite journal |last1=Diehl |first1=J. J. E. |last2=Baines |first2=F. M. |last3=Heijboer |first3=A. C. |last4=van Leeuwen |first4=J. P. |last5=Kik |first5=M. |last6=Hendriks |first6=W. H. |last7=Oonincx |first7=D. G. A. B. |date=February 2018 |title=A comparison of UVb compact lamps in enabling cutaneous vitamin D synthesis in growing bearded dragons |journal=Journal of Animal Physiology and Animal Nutrition |language=en |volume=102 |issue=1 |pages=308–316 |doi=10.1111/jpn.12728 |pmid=28452197 |s2cid=30124686 |doi-access=free }}</ref> Specifically [[Chemistry:Cholecalciferol|cholecalciferol]] (vitamin D3), which is needed for basic cellular / neural functioning as well as the utilization of calcium for bone and egg production.{{Citation needed|date=April 2022}} The UVA wavelength is also visible to many reptiles and might play a significant role in their ability survive in the wild as well as in visual communication between individuals.{{Citation needed|date=April 2022}} Therefore, in a typical reptile enclosure, a fluorescent UV a/b source (at the proper strength / spectrum for the species), must be available for many{{Which|date=April 2022}} captive species to survive. Simple supplementation with [[Chemistry:Cholecalciferol|cholecalciferol]] (Vitamin D3) will not be enough as there's a complete biosynthetic pathway{{Which|date=May 2022}} that is "leapfrogged" (risks of possible overdoses), the intermediate molecules and metabolites{{Which|date=April 2022}} also play important functions in the animals health.{{Citation needed|date=April 2022}} Natural sunlight in the right levels is always going to be superior to artificial sources, but this might not be possible for keepers in different parts of the world.{{Citation needed|date=April 2022}}

It is a known problem that high levels of output of the UVa part of the spectrum can both cause cellular and DNA damage to sensitive parts of their bodies – especially the eyes where blindness is the result of an improper UVa/b source use and placement photokeratitis.{{Citation needed|date=April 2022}} For many keepers there must also be a provision for an adequate heat source this has resulted in the marketing of heat and light "combination" products.{{Citation needed|date=April 2022}} Keepers should be careful of these "combination" light/ heat and UVa/b generators, they typically emit high levels of UVa with lower levels of UVb that are set and difficult to control so that animals can have their needs met.{{Citation needed|date=April 2022}} A better strategy is to use individual sources of these elements and so they can be placed and controlled by the keepers for the max benefit of the animals.<ref>{{cite web|url=http://www.uvguide.co.uk/vitdpathway.htm|title=Vitamin D and Ultraviolet Light – a remarkable process|website=UV Guide UK|access-date=2017-01-13|url-status=live|archive-url=https://web.archive.org/web/20160531172209/http://www.uvguide.co.uk/vitdpathway.htm|archive-date=31 May 2016}}</ref>

==Evolutionary significance==
The evolution of early reproductive [[Biology:Proteins|proteins]] and [[Biology:Enzymes|enzymes]] is attributed in modern models of evolutionary theory to ultraviolet radiation. UVB causes [[Chemistry:Thymine|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. This leads to frameshifting during genetic replication and protein synthesis, usually killing the cell. Before formation of the UV-blocking ozone layer, when early [[Biology:Prokaryote|prokaryote]]s approached the surface of the ocean, they almost invariably died out. The few that survived had developed enzymes that monitored the genetic material and removed thymine dimers by [[Biology:Nucleotide excision repair|nucleotide excision repair]] enzymes. Many enzymes and proteins involved in modern [[Biology:Mitosis|mitosis]] and [[Biology:Meiosis|meiosis]] are similar to repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome DNA damages caused by UV.<ref>{{Cite book |author1=Margulis, Lynn |author2=Sagan, Dorion |name-list-style=amp | title = Origins of Sex: Three Billion Years of Genetic Recombination | version = 1 | publisher = Yale University Press |year=1986 | url = https://books.google.com/books?id=3hDVTEk3ioIC&q=origins+of+sex:+three&pg=PP1 | isbn = 978-0-300-04619-9 | format = book}}</ref>

==Photobiology==
{{main|Biology:Photobiology}}

Photobiology is the scientific study of the beneficial and harmful interactions of non-ionizing radiation in living organisms, conventionally demarcated around 10 eV, the first ionization energy of oxygen. UV ranges roughly from 3 to 30 eV in energy. Hence photobiology entertains some, but not all, of the UV spectrum.

==See also==
{{colbegin|colwidth=18em}}
* [[Biology:Biological effects of high-energy visible light|Biological effects of high-energy visible light]]
* [[Physics:Infrared|Infrared]]
* [[Astronomy:Ultraviolet astronomy|Ultraviolet astronomy]]
* [[Physics:Ultraviolet catastrophe|Ultraviolet catastrophe]]
* [[Astronomy:Ultraviolet index|Ultraviolet index]]
* UV marker
* UV stabilizers in plastics
* [[Chemistry:Weather testing of polymers|Weather testing of polymers]]
{{colend}}

==References==
{{reflist}}

==Further reading==
* {{Cite book| last = Allen| first = Jeannie| title = Ultraviolet Radiation: How it Affects Life on Earth| url =http://earthobservatory.nasa.gov/Features/UVB/|date=6 September 2001| series = Earth Observatory| publisher = NASA, USA}}
* {{Cite journal | last = Hockberger | first = Philip E. | title = A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms | journal =Photochemistry and Photobiology | volume =76 | issue =6 | pages =561–569 | year =2002 | doi = 10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2 | pmid=12511035| s2cid = 222100404 }}
* {{Cite journal | last1 = Hu | first1 = S | last2 = Ma | first2 = F | last3 = Collado-Mesa | first3 = F | last4 = Kirsner | first4 = R. S. | title = UV radiation, latitude, and melanoma in US Hispanics and blacks | journal = Arch. Dermatol. | volume = 140 | issue = 7 | pages = 819–824 |date=July 2004 | doi = 10.1001/archderm.140.7.819 | pmid = 15262692 | doi-access = free }}
* {{Cite journal | last1 = Strauss | first1 = CEM | last2 = Funk | first2 = DJ | title = Broadly tunable difference-frequency generation of VUV using two-photon resonances in H2 and Kr | journal = Optics Letters | volume = 16 | issue = 15 | pages = 1192–4 |date=1991 | doi=10.1364/ol.16.001192 | pmid = 19776917 | bibcode = 1991OptL...16.1192S}}

== External links ==

{{EMSpectrum}}

[[Category:Electromagnetic radiation]]
[[Category:Electromagnetic spectrum]]
[[Category:Ultraviolet radiation]]

{{Sourceattribution|Ultraviolet}}