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ultraviolet
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{{short description|Electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays}}{{other uses}}{{redirect|UV}}{{pp-move-indef}}{{Use dmy dates|date=August 2013}}{{multiple image
|direction = horizontal
|align = right
|image1 = UV-handlamp hg.jpg
|caption1 = Portable ultraviolet lamp
|width1 = 110
|image2 = Pipefitter welder kutzo.jpg
|caption2 = UV radiation is also produced by electric arcs. Arc welders must wear eye protection and cover their skin to prevent photokeratitis and serious sunburn.
|width2 = 240
|footer =
}}Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total output of the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.Suntan and sunburn are familiar effects of over-exposure of the skin to UV, along with higher risk of skin cancer. Living things on dry land would be severely damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earth's atmosphere.WEB,weblink Reference Solar Spectral Irradiance: Air Mass 1.5, 2009-11-12, yes,weblink" title="web.archive.org/web/20110127004149weblink">weblink 27 January 2011, dmy-all, More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground.JOURNAL, Haigh, Joanna D. ., 2007, The Sun and the Earth's Climate: Absorption of solar spectral radiation by the atmosphere, Living Reviews in Solar Physics, 4, 2, 2,weblink July 12, 2014, 10.12942/lrsp-2007-2, 2007LRSP....4....2H, no,weblink" title="web.archive.org/web/20160304050402weblink">weblink 4 March 2016, dmy-all, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans (specifically, UVB).JOURNAL, Wacker, Matthias, Holick, Michael F., 2013-01-01, Sunlight and Vitamin D, Dermato-endocrinology, 5, 1, 51–108, 10.4161/derm.24494, 1938-1972, 3897598, 24494042, The UV spectrum thus has effects both beneficial and harmful to human health.The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although some people can perceive light at slightly shorter wavelengths than this (see below). Insects, birds, and some mammals can see near-UV (i.e. slightly lower wavelengths than humans can see).{{TOC limit|3}}

Visibility

Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea.JOURNAL, Violet and blue light blocking intraocular lenses: photoprotection versus photoreception, British Journal of Ophthalmology, 2006, 90, 784–792, M A Mainster, 1860240, 16714268, 10.1136/bjo.2005.086553, 6, Humans lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the 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.NEWS, Let the light shine in, David Hambling, The Guardian, 29 May 2002,weblink 2 January 2015, no,weblink" title="web.archive.org/web/20141123170913weblink">weblink 23 November 2014, dmy-all, Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm.BOOK, Lynch, David K., Livingston, William Charles, Color and Light in Nature,weblink 12 October 2013, 2nd, 2001, Cambridge University Press, Cambridge, UK, 978-0-521-77504-5, 231, Limits of the eye's overall range of sensitivity extends from about 310 to 1050 nanometers, no,weblink" title="web.archive.org/web/20131231214332weblink">weblink 31 December 2013, dmy-all, BOOK, Dash, Madhab Chandra, Dash, Satya Prakash, Fundamentals Of Ecology 3E,weblink 18 October 2013, 2009, Tata McGraw-Hill Education, 978-1-259-08109-5, 213, 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., no,weblink" title="web.archive.org/web/20131231214338weblink">weblink 31 December 2013, dmy-all, Near-UV radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.WEB,weblink Want ultraviolet vision? You're going to need smaller eyes, Joseph, Bennington-Castro, no,weblink" title="web.archive.org/web/20160507082220weblink">weblink 7 May 2016, dmy-all, JOURNAL, Hunt, D. M., Carvalho, L. S., Cowing, J. A., Davies, W. L., Evolution and spectral tuning of visual pigments in birds and mammals, Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 1531, 2009, 2941–2955, 0962-8436, 10.1098/rstb.2009.0044, 19720655, 2781856,

Discovery

"Ultraviolet" means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the highest frequencies of visible light. Ultraviolet has a higher frequency (and thus a shorter wavelength) than violet light.UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "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 John William Draper, who named them "tithonic rays""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"Description of the Tithonometer", J.W. Draper, The Practical Mechanic and Engineer's Magazine, January 1844, pp.122–127). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and infrared radiation, respectively.BOOK, Beeson, Steven, Mayer, James W, Patterns of light: chasing the spectrum from Aristotle to LEDs, Springer, New York, 978-0-387-75107-8, 149, 12.2.2 Discoveries beyond the visible, 2007-10-23, JOURNAL
, Hockberger
, Philip E.
, A history of ultraviolet photobiology for humans, animals and microorganisms
, Photochem. Photobiol.
, 76
, 6
, 561–79
, 2002
, 10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2
, 12511035
, In 1878 the sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established.James Bolton, Christine Colton, The Ultraviolet Disinfection Handbook, American Water Works Association, 2008 {{ISBN|978 1 58321 584 5}}, pp. 3–4The discovery of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by the German physicist Victor Schumann.The ozone layer also protects living beings from this.JOURNAL
, Lyman
, T.
, Victor Schumann
, Astrophysical Journal
, 38
, 1–4
, 1914
, 1914ApJ....39....1L
, 10.1086/142050
,

Subtypes

The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO-21348:WEB, ISO 21348 Definitions of Solar Irradiance Spectral Categories,weblink no,weblink" title="web.archive.org/web/20131029233428weblink">weblink 29 October 2013, dmy-all, {| class="wikitable" style="margin:2em auto; text-align:center;"! Name! Abbreviation! Wavelength(nm)! Photon energy(eV, aJ)! Notes/alternative names
| Ultraviolet A| UVA| 315–400
3.103.94aJdisp=br()}}| Long-wave, black light, not absorbed by the ozone layer: soft UV
| Ultraviolet B| UVB| 280–315
3.944.43aJdisp=br()}}| Medium-wave, mostly absorbed by the ozone layer: intermediate UV
| Ultraviolet C| UVC| 100–280
4.4312.4aJdisp=br()}}Ultraviolet germicidal irradiation>germicidal, completely absorbed by the ozone layer and atmosphere: hard UV
| Near ultraviolet| NUV| 300–400
3.104.13aJdisp=br()}}
| Middle ultraviolet| MUV| 200–300
4.136.20aJdisp=br()}}|
| Far ultraviolet| FUV| 122–200
6.2010.16aJdisp=br()}}|
Lyman-alpha line>Lyman-alpha| H Lyman-α| 121–12210.1610.25aJdisp=br()}}| Spectral line at 121.6 nm, 10.20 eV.Ionizing radiation at shorter wavelengths
| Vacuum ultraviolet| VUV| 10–200
6.20124aJdisp=br()}}| Strongly absorbed by atmospheric oxygen,though 150–200 nm wavelengths can propagate through nitrogen
| Extreme ultraviolet| EUV| 10–121
10.25124abbr=valuesaJ}}| Entirely ionizing radiation by some definitions;completely absorbed by the atmosphere
A variety of 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 photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are available. Spectrometers and radiometers are made for measurement of UV radiation. Silicon detectors are used across the spectrum.WEB,weblinkweblink" title="web.archive.org/web/20090109215922weblink">weblink 2009-01-09, Gullikson, Korde, Canfield, Vest, " Stable Silicon Photodiodes for absolute intensity measurements in the VU V and soft x-ray regions", Jrnl of Elec. Spect. and Related Phenomena 80(1996) 313–316, Ts.nist.gov, 2011-11-08, Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths of about 150–200 nm can propagate through nitrogen. Scientific instruments can therefore utilize 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 photolithography equipment (for semiconductor manufacturing) and 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 "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 nm interact mainly with the outer valence electrons 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+ spectral line at 30.4 nm. EUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50 percent of EUV radiation at normal incidence. This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the Extreme Ultraviolet Explorer (EUVE) satellite.File:Ozone altitude UV graph.svg|thumb|upright=1.25|Levels of ozone at various altitudes (w:Dobson unit|DU/km]]) and blocking of different bands of ultraviolet radiation. In essence, all UVC is blocked by diatomic oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone, and most of it reaches the ground. UVA makes up almost all of the circa 25 percent of the Sun's total UV light that penetrates the Earth's atmosphere.]]Some sources use the distinction of "hard UV" and "soft UV" - in the case of astrophysics the boundary may be at the Lyman limit i.e. wavelength 91.2 nm, with "hard UV" being more energetic.{{citation| title =The Birth of Stars and Planets| first = John| last = Bally| first2 = Bo | last2 = Reipurth | page =177| publisher = Cambridge University Press | year = 2006 }} The same terms may also used in other fields, such as cosmetology, optoelectronic, etc. - the numerical value 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 nm between hard and soft UV regions.{{citation| title = Slipping surface discharge as a source of hard UV radiation | journal = Journal of Physics D: Applied Physics | volume =33 | pages = 859 | number = 7 | url =http://stacks.iop.org/0022-3727/33/i=7/a=317 | bibcode = 2000JPhD...33..859B | 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 | doi = 10.1088/0022-3727/33/7/317 }}

Solar ultraviolet

Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum.WEB,weblink Solar radiation, no,weblink" title="web.archive.org/web/20121101070344weblink">weblink 1 November 2012, dmy-all, 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.WEB,weblink Introduction to Solar Radiation, www.newport.com, no,weblink" title="web.archive.org/web/20131029234117weblink">weblink 29 October 2013, dmy-all, WEB,weblink Reference Solar Spectral Irradiance: Air Mass 1.5, 2009-11-12, no,weblink" title="web.archive.org/web/20130928011257weblink">weblink 28 September 2013, dmy-all, Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. There is essentially no UVC.{{citation|url=http://www.skincancer.org/prevention/uva-and-uvb/understanding-uva-and-uvb|title=Understanding UVA and UVB|accessdate=2012-04-30|deadurl=no|archiveurl=https://web.archive.org/web/20120501231522weblink|archivedate=1 May 2012|df=dmy-all}} The fraction of UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. Thick clouds may block up to 90% of UVB radiation,"What does SPF Mean?" but in "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by Rayleigh scattering in the same way as the visible blue light from those parts of the sky. UV-B also plays a major role in plant development as it affects most of the plant hormones.{{citation|url=https://academic.oup.com/jxb/article/67/15/4469/1750169|archive-url=https://web.archive.org/web/20160708010101weblink|title=Hormone-controlled UV-B responses in plants|deadurl=yes|archivedate=8 July 2016|df=dmy-all}}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 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 and absorbers

Ultraviolet absorbers are molecules used in organic materials (polymers, paints, etc.) to absorb UV radiation to reduce the 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 sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone, oxybenzoneJOURNAL, Burnett, M. E., Wang, S. Q., 2011, Current sunscreen controversies: a critical review, Photodermatology, Photoimmunology & Photomedicine, 27, 2, 58–67, 10.1111/j.1600-0781.2011.00557.x, 21392107, and octyl methoxycinnamate, are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as carbon black, titanium dioxide and 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 SPF (Sun Protection Factor) ratings for sunscreen. Standard summer fabrics have UPF of approximately 6, which means that about 20% of UV will pass through.Suspended nanoparticles in stained glass prevent UV rays from causing chemical reactions that change image colors. 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.WEB,weblink How medieval stained-glass is creating the ultimate SPACE camera: Nanoparticles used in church windows will help scientists see Mars' true colours under extreme UV light, ELLIE ZOLFAGHARIFARD, 15 October 2013, no,weblink" title="archive.today/20131228213901weblink">weblink 28 December 2013, dmy-all, Common soda–lime glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas fused quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.WEB, Soda Lime Glass Transmission Curve,weblink no,weblink" title="web.archive.org/web/20120327213950weblink">weblink 27 March 2012, dmy-all, WEB,weblink B270-Superwite Glass Transmission Curve, Präzisions Glas & Optik, 2017-01-13, no,weblink 9 July 2017, dmy-all, WEB,weblink Selected Float Glass Transmission Curve, Präzisions Glas & Optik, 2017-01-13, no,weblink" title="web.archive.org/web/20151019025929weblink">weblink 19 October 2015, dmy-all, Wood's glass is a nickel-bearing form of glass with a deep blue-purple color that blocks most visible light and passes ultraviolet.

Artificial sources

"Black lights"

{{multiple image|direction = vertical|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 inch, 15 watt tube, shown in the bottom image in a standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12 inch, 8 watt tube, used in a portable battery-powered black light sold as a pet urine detector.}}A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple Wood's glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometres.WEB,weblink Insect-O-Cutor, no,weblink" title="web.archive.org/web/20130604215247weblink">weblink 4 June 2013, dmy-all, Others 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 fraction of a percent of their power as UV. Mercury-vapor black lights in ratings up to 1 kW with UV-emitting phosphor and an envelope of 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 fluorescence, the colored glow that many substances give off when exposed to UV light. UVA/UVB emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-keeping.

Short-wave ultraviolet lamps

{{multiple image| align = right| direction = vertical| header =| image1 = Germicidal Lamp 1.jpg| caption1 = 9-watt germicidal UV lamp, in compact fluorescent (CF) form factor| image2 = Кварцевая лампа.JPG| caption2 = Commercial germicidal lamp in butcher shop| width = 200}}Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz, since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in the UVC band at 253.7 nm and 185 nm due to the 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 nm, whereas only 5–10% is at 185 nm.{{Citation needed|date=November 2012}} The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UVC power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–40 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. Halogen lamps with fused quartz envelopes are used as inexpensive UV light sources in the near UV range, from 400 to 300 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

Specialized UV gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes. Argon and deuterium arc lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride.JOURNAL,weblink Klose, Jules Z., Bridges, J. Mervin, Ott, William R., NBS Measurement Services: Radiometric Standards in the VUV, NBS Special Publication, 250–3, June 1987, no,weblink" title="web.archive.org/web/20160611075213weblink">weblink 11 June 2016, dmy-all, 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), deuterium arc lamps, mercury-xenon arc lamps, and metal-halide arc lamps.The 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|A 380 nanometre 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, UVA LEDs of 365 nm and longer wavelength were available with efficiencies of 50 percent at 1000 mW output. Such LEDs are increasingly used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. Power densities approaching 3 W/cm2 (30 kW/m2) are now possible, and this, coupled with recent developments by photoinitiator and resin formulators, makes the expansion of LED-cured UV materials likely.UVC LEDs are beginning to be used in disinfectionJOURNAL, Boyce, JM, Modern technologies for improving cleaning and disinfection of environmental surfaces in hospitals, Antimicrobial Resistance and Infection Control, 2016, 5, 10, 27069623, 4827199, 10.1186/s13756-016-0111-x, and as line sources to replace deuterium lamps in liquid chromatography instruments.WEB,weblink UVC LEDs Enhance Chromatography Applications - GEN, GEN, no,weblink" title="web.archive.org/web/20161104020423weblink">weblink 4 November 2016, dmy-all,

Ultraviolet lasers

Gas lasers, laser diodes and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available which 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 nm and 357.6.6 nm, wavelength. Another type of high power gas laser is the excimer laser. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride (ArF) excimer lasers operating at 193 nm are routinely used in integrated circuit production by photolithography. The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar2* excimer laser.Direct UV-emitting laser diodes are available at 375 nm.WEB,weblink UV Laser Diode: 375 nm Center Wavelength, Thorlabs, United States, Product Catalog, 14 December 2014, UV diode-pumped solid state lasers have been demonstrated using Ce:LiSAF crystals (cerium-doped lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory.WEB
, Marshall
, Chris
, A simple, reliable ultraviolet laser: the Ce:LiSAF
, Lawrence Livermore National Laboratory
, 1996
,weblink
, 2008-01-11
, no
,weblink
, 20 September 2008
, dmy-all
, Wavelengths shorter than 325 nm are commercially generated in diode-pumped solid-state lasers. Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers.Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology, and keratectomy), chemistry (MALDI), free air secure communications, computing (optical storage) and manufacture of integrated circuits.

Tunable vacuum ultraviolet (VUV) via sum and difference frequency mixing

The vacuum ultraviolet (VUV) band (100–200 nm) can be generated by non-linear 4 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 nm) or metal vapors (e.g. magnesium). By making one of the lasers tunable, the VUV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the VUV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. Difference frequency mixing (lambda1 + lambda2 − lambda3) has an advantage over sum frequency mixing because the phase matching can provide greater tuning. In particular, difference frequency mixing two photons of an ArF (193 nm) excimer laser with a tunable visible or near IR laser in hydrogen or krypton provides resonantly enhanced tunable VUV covering from 100 nm to 200 nm.
JOURNAL, Strauss
, CEM
, Funk
, DJ
, Broadly tunable difference-frequency generation of VUV using two-photon resonances in H2 and Kr
, Optics Letters
, 16
, 15
, 1192
, 1991
,weblink
, 10.1364/ol.16.001192
, 1991OptL...16.1192S
,
Practically, the lack of suitable gas/vapor cell window materials above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable VUV wavelengths down to 75 nm was achieved using window-free configurations.
JOURNAL
, Xiong
, Bo
, Chang
, Yih-Chung
, Ng
, Cheuk-Yiu
, Quantum-state-selected integral cross sections for the charge transfer collision of O2+(a4Πu5/2,3/2,1/2,−1/2: v+=1–2; J+) [O2+(X2Πg3/2,1/2: v+=22–23; J+)] + Ar at center-of-mass collision energies of 0.05–10.00 eV
, Phys. Chem. Chem. Phys.
, 2017
,weblink
, 10.1039/C7CP04886F
, 28920600
, no
,weblink" title="web.archive.org/web/20171115202941weblink">weblink
, 15 November 2017
, dmy-all
, 19
, 43
, 29057–29067, 2017PCCP...1929057X
,

Plasma and synchrotron sources of extreme UV

Lasers have been used to indirectly generate non-coherent extreme UV (EUV) radiation at 13.5 nm for extreme ultraviolet lithography. The EUV 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.WEB,weblink EUV Nudges Toward 10nm - EE Times, EETimes, no,weblink" title="web.archive.org/web/20141015014640weblink">weblink 15 October 2014, dmy-all, This technique does not require a synchrotron, yet can produce UV at the edge of the X-ray spectrum. Synchrotron light sources can also produce all wavelengths of UV, including those at the boundary of the UV and X-ray spectra at 10 nm.

Human health-related effects

{{Further|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 fluorescent lamps and health. Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial.JOURNAL, Sivamani, RK, Crane, LA, Dellavalle, RP, The benefits and risks of ultraviolet tanning and its alternatives: the role of prudent sun exposure, Dermatologic Clinics, April 2009, 27, 2, 149–54, vi, 19254658, 10.1016/j.det.2008.11.008, 2692214,

Beneficial effects

There is no doubt that a little sunlight is good for you! But 5 to 15 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.
— World Health Organization
UV light causes the body to produce vitamin D (specifically, UVB), which is essential for life. The human body needs some UV radiation in order for one to maintain adequate vitamin D levels; however, excess exposure produces harmful effects that typically outweigh the benefits."The known health effects of UV, Ultraviolet radiation and the INTERSUN Programme" {{webarchive|url=https://web.archive.org/web/20161016090300weblink |date=16 October 2016 }}, World Health Organization.Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives.Korb, Alex, "Boosting Your Serotonin Activity" {{webarchive|url=https://archive.today/20170801135657weblink |date=1 August 2017 }}. Psychology Today, 17 November 2011. Serotonin is thought to provide sensations of happiness, well being and serenity to human beings.JOURNAL, 2077351, 2007, Young, S. N., How to increase serotonin in the human brain without drugs, Journal of Psychiatry and Neuroscience, 32, 6, 394–399, 18043762,

Skin conditions

UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma.JOURNAL, Juzeniene, Asta, Moan, Johan, Beneficial effects of UV radiation other than via vitamin D production, Dermato-Endocrinology, 27 October 2014, 4, 2, 109–117, 10.4161/derm.20013, 22928066, 3427189, "Health effects of ultraviolet radiation" {{webarchive|url=https://web.archive.org/web/20161008013441weblink |date=8 October 2016 }}. Government of Canada. In addition, UV light, in particular UVB radiation, has been shown to induce cell cycle arrest in keratinocytes, the most common type of skin cell.JOURNAL, Ultraviolet B irradiation-induced G2 cell cycle arrest in human keratinocytes by inhibitory phosphorylation of the cdc2 cell cycle kinase, Oncogene, 11, 10, 2151–6, 7478536, 1995, Herzinger, T, Funk, J. O, Hillmer, K, Eick, D, Wolf, D. A, Kind, P, 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.JOURNAL, Excimer laser therapy and narrowband ultraviolet B therapy for exfoliative cheilitis, International Journal of Women's Dermatology, 1, 2, 95–98, 10.1016/j.ijwd.2015.01.006, 28491966, 5418752, 2015, Bhatia, Bhavnit K., Bahr, Brooks A., Murase, Jenny E.,

Harmful effects

In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and retina. The risk is elevated at high altitudes and people living in high latitude countries where snow covers the ground right into early summer and sun positions even at zenith are low, are particularly at risk.JOURNAL, Meyer-Rochow, Victor Benno, Risks, especially for the eye, emanating from the rise of solar UV-radiation in the Arctic and Antarctic regions, International Journal of Circumpolar Health, 2000, 59, 1, 38–51, 10850006, Skin, the circadian and immune systems can also be affected.WEB, Health effects of UV radiation,weblink World Health Organization, no,weblink" title="web.archive.org/web/20150317041542weblink">weblink 17 March 2015, dmy-all, 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 dimerthymine dimerFile:Erythemal action spectrum.svg|thumb|right|Sunburn effect (as measured by the UV IndexUV IndexThe differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum".WEB,weblink Navy Ultraviolet Radiation Guide, no,weblink" title="web.archive.org/web/20150617013119weblink">weblink 17 June 2015, dmy-all, The action spectrum shows that UVA does not cause immediate reaction, but rather UV begins to cause photokeratitis and skin redness (with Caucasians more sensitive) at wavelengths starting near the beginning of the UVB band at 315 nm, and rapidly increasing to 300 nm. The skin and eyes are most sensitive to damage by UV at 265–275 nm, which is in the lower UVC 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 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 UVA and UVB bands.

Skin damage

Overexposure to UVB radiation not only can cause sunburn but also some forms of skin cancer. However, the degree of redness and eye irritation (which are largely not caused by UVA) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet.WEB,weblink What Is Ultraviolet (UV) Radiation?, www.cancer.org, 2017-06-11, no,weblink 3 April 2017, dmy-all, All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.JOURNAL, Torma, H, Berne, B, Vahlquist, A, Acta Derm. Venereol., 1988, 68, 4, 291–299, UV irradiation and topical vitamin A modulate retinol esterification in hairless mouse epidermis, 2459873, UVB radiation can cause direct DNA damage.JOURNAL, Bernstein C, Bernstein H, Payne CM, Garewal H, DNA repair/pro-apoptotic dual-role proteins in five major DNA repair pathways: fail-safe protection against carcinogenesis, Mutat. Res., 511, 2, 145–78, June 2002, 12052432, 10.1016/S1383-5742(02)00009-1, This cancer connection is one reason for concern about ozone depletion and the ozone hole.The most deadly form of skin cancer, malignant melanoma, is mostly caused by DNA damage independent from UVA radiation. This can be seen from the absence of a direct UV signature mutation in 92% of all melanoma.JOURNAL, Davies H., Bignell G. R., Cox C., June 2002, Mutations of the BRAF gene in human cancer, Nature, 417, 6892, 949–954, 10.1038/nature00766, 12068308, dmy-all, Occasional overexposure and sunburn are probably greater risk factors for melanoma than long-term moderate exposure.JOURNAL, Richard Weller, Shunning the sun may be killing you in more ways than you think, New Scientist, Jun 10, 2015,weblink no,weblink 9 June 2017, dmy-all, UVC is the highest-energy, most-dangerous type of ultraviolet radiation, and causes adverse effects that can variously be mutagenic or carcinogenic.C.Michael Hogan. 2011. Sunlight. eds. P.Saundry & C.Cleveland. Encyclopedia of Earth. {{webarchive|url=https://web.archive.org/web/20131019060416weblink |date=19 October 2013 }}In the past, UVA was considered not harmful or less harmful than UVB, but today it is known to contribute to skin cancer via indirect DNA damage (free radicals such as reactive oxygen species). UVA 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 UVA consists mostly of single-strand breaks in DNA, while the damage caused by UVB includes direct formation of thymine dimers or other pyrimidine dimers and double-strand DNA breakage.JOURNAL, 22271212, 10.1007/s00403-012-1212-x, DNA damage after acute exposure of mice skin to physiological doses of UVB and UVA light, January 2012, Arch Dermatol Res, Svobodová AR, Galandáková A, Sianská J, etal, 304, 5, 407–412, UVA 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.JOURNAL, 22123419, 10.1016/j.sder.2011.08.002, 30, 4, Ultraviolet A radiation: its role in immunosuppression and carcinogenesis, December 2011, Semin Cutan Med Surg, 214–21, Halliday GM, Byrne SN, Damian DL, UVB photons can cause direct DNA damage. UVB radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent pyrimidine bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins. Those pyrimidine dimers that escape this repair process can induce a form of programmed cell death (apoptosis) or can cause DNA replication errors leading to mutation.As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, protecting the skin against both direct and indirect DNA damage from the UV. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.

Sunscreen safety debate

(File:UV and Vis Sunscreen.jpg|thumb|left|Demonstration of the effect of sunscreen. The man's face has sunscreen on his right only. The left image is a regular photograph of the face; the right image is taken by 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 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.JOURNAL, Xu, C., Green, Adele, Parisi, Alfio, Parsons, Peter G, 2001, Photosensitization of the Sunscreen Octyl p-Dimethylaminobenzoate b UVA in Human Melanocytes but not in Keratinocytes, Photochemistry and Photobiology, 73, 6, 600–604, 10.1562/0031-8655(2001)0732.0.CO;2, 11421064, JOURNAL, Knowland, John, McKenzie, Edward A., McHugh, Peter J., Cridland, Nigel A., Sunlight-induced mutagenicity of a common sunscreen ingredient, FEBS Letters, 324, 309–313, 1993, 8405372, 10.1016/0014-5793(93)80141-G, 3, The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage.Chatelaine, E.; Gabard, B.; Surber, C. (2003) pdf Skin Penetration and Sun Protection Factor of Five UV Filters: Effect of the Vehicle {{webarchive|url=https://web.archive.org/web/20131227063745weblink |date=27 December 2013 }}, Skin Pharmacol. Appl. Skin Physiol., 16:28–35 {{doi|10.1159/000068291}} {{PMID|12566826}}Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UVB, and the usual SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UVB protection factor".JOURNAL, 21283919, 10, 2, The impact of natural sunlight exposure on the UVB-sun protection factor (UVB-SPF) and UVA protection factor (UVA-PF) of a UVA/UVB SPF 50 sunscreen, February 2011, J Drugs Dermatol, 150–155, Stephens TJ, Herndon JH, Colón LE, Gottschalk RW, This rating, however, offers no data about important protection against UVA,JOURNAL, 21669263, 10.1016/j.ijpharm.2011.05.071, 415, 1–2, Sunscreen products: what do they protect us from?, August 2011, Int J Pharm, 181–4, Couteau C, Couteau O, Alami-El Boury S, Coiffard LJ, 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 UVA filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users.JOURNAL, Garland C, Garland F, Gorham E, Could sunscreens increase melanoma risk?, Am J Public Health, 82, 4, 614–5, 1992, 1546792, 10.2105/AJPH.82.4.614, 1694089, JOURNAL, Westerdahl J, Ingvar C, Masback A, Olsson H, Sunscreen use and malignant melanoma, International Journal of Cancer, 87, 1, 145–150, 2000, 10.1002/1097-0215(20000701)87:13.0.CO;2-3, 10861466, JOURNAL, Autier P, Dore JF, Schifflers E, Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France, Int. J. Cancer, 61, 6, 749–755, 1995, 10.1002/ijc.2910610602, 7790106, etal, JOURNAL, Weinstock, M. A., Do sunscreens increase or decrease melanoma risk: An epidemiologic evaluation, Journal of Investigative Dermatology Symposium Proceedings, 4, 1, 97–100, 1999, 10537017, 10.1038/sj.jidsp.5640190, 2019-05-24, JOURNAL, Vainio, H., Bianchini, F., Cancer-preventive effects of sunscreens are uncertain, Scandinavian Journal of Work Environment and Health, 26, 529–531, 2000, 10.5271/sjweh.578, Some sunscreen lotions now contain compounds including titanium dioxide, zinc oxide and avobenzone which helps protect against UVA rays.The photochemical properties of melanin make it an excellent 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 reactive oxygen species may be increased.JOURNAL, Hanson Kerry M., Gratton Enrico, Bardeen Christopher J., Sunscreen enhancement of UV-induced reactive oxygen species in the skin, 10.1016/j.freeradbiomed.2006.06.011, Free Radical Biology and Medicine, 41, 8, 1205–1212, 2006, 17015167,weblink JOURNAL, Damiani, E., Greci, L., Parsons, R., Knowland, Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient, Free Radic. Biol. Med., 26, 7–8, 809–816, 1999, 10.1016/S0891-5849(98)00292-5, The amount of sunscreen that penetrates through the 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 reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin. The study indicates that sunscreen must be reapplied within 2 hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.

Aggravation of certain skin conditions

Ultraviolet radiation can aggravate several skin conditions and diseases, includingEuropean Guidelines for Photodermatoses > 2 Photoaggravated Disorders{{dead link|date=January 2016}} at European Dermatology Forum systemic lupus erythematosus, Sjögren's syndrome, Sinear Usher syndrome, rosacea, dermatomyositis, Darier's disease, and Kindler–Weary syndrome.

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 UVC band at 265–275 nm. Radiation of this wavelength is almost absent from sunlight but is found in welder's arc lights and other artificial sources. Exposure to these can cause "welder's flash" or "arc eye" (photokeratitis) and can lead to cataracts, pterygium and pinguecula formation. To a lesser extent, UVB in sunlight from 310–280 nm also causes photokeratitis ("snow blindness"), and the cornea, the lens, and the retina can be damaged.WEB,weblink The known health effects of UV, World Health Organization, no,weblink" title="web.archive.org/web/20161024170159weblink">weblink 24 October 2016, dmy-all, 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.WEB,weblink UV radiation, World Health Organization, no,weblink" title="web.archive.org/web/20161025234856weblink">weblink 25 October 2016, dmy-all, WEB,weblink What is UV radiation and how much does it increase with altitude?, NOAA, no,weblink" title="web.archive.org/web/20170103102305weblink">weblink 3 January 2017, dmy-all, Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate, inherently block most UV.WEB,weblink Optical properties of lens materials - Optician, www.opticianonline.net, no,weblink 26 October 2016, dmy-all,

Degradation of polymers, pigments and dyes

File:Failedrope1.jpg|thumb|left|UV damaged polypropylenepolypropyleneUV degradation is one form of polymer degradation that affects plastics exposed to 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.Sensitive polymers include thermoplastics and speciality fibers like aramids. 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.File:Irspec2.jpg|thumb|right|IR spectrum showing carbonyl absorption due to UV degradation of polyethylenepolyethyleneMany pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, 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 fluorescence in materials, ultraviolet radiation has a number of applications. The following tableWEB,weblink s-et.com, 2009-09-26, usurped,weblink" title="web.archive.org/web/20080820022822weblink">weblink 20 August 2008, dmy-all, gives some uses of specific wavelength bands in the UV spectrum

Photography

(File:UV Portrait.jpg|thumb|upright=0.9|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 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 nm requires special quartz lenses which do not absorb the radiation.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 (phenomenon)|Aurora at Jupiter's north pole as seen in ultraviolet light by the Hubble Space TelescopeHubble Space TelescopeIn 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

Corona discharge on electrical apparatus can be detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of ozone and nitrogen oxide.WEB, Corona – The Daytime UV Inspection Magazine,weblink no,weblink" title="web.archive.org/web/20040801222232weblink">weblink 1 August 2004, dmy-all, EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent (quartz) window on the top of the chip that allows the UV radiation in.

Fluorescent dye uses

Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners 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. Blacklight paints 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, biochemistry and forensics). Some brands of pepper spray will leave an invisible chemical (UV dye) that is not easily washed off on a pepper-sprayed attacker, which would help police identify the attacker later.WEB, Pepper Spray FAQ,weblink yes,weblink" title="web.archive.org/web/20130615064211weblink">weblink 15 June 2013, In some types of 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.JOURNAL, Springer, E, Almog, J, Frank, A, Ziv, Z, Bergman, P, Gui Quang, W, 1994, Detection of dry bodily fluids by inherent short wavelength UV luminescence: Preliminary results, Forensic Sci Int, 66, 2, 89–94, 10.1016/0379-0738(94)90332-8, 8063277, 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.WEB,weblink Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source, Anja Fiedler, Mark Benecke, 2009-12-10, etal, yes,weblink" title="web.archive.org/web/20121130113644weblink">weblink 30 November 2012, 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 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.WEB, Digital Photography of Documents,weblinkweblink" title="archive.today/20120919133157weblink">weblink yes, 2012-09-19, wells-genealogy.org.uk,

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 equipmentpersonal protective equipmentUltraviolet aids in the detection of organic material deposits that remain on surfaces where periodic cleaning and sanitizing may not have been properly accomplished. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected.WEB, Integrated Cleaning And Measurement: Defining - What is Clean?,weblink Healthy Facilities Institute, 24 June 2017, en, yes,weblink" title="web.archive.org/web/20170921171252weblink">weblink 21 September 2017, dmy-all, WEB, Non-Destructive Inspection: Seeing Through the B-52,weblink US Air Force, 24 June 2017, NEWS, Escobar, David, Oxygen Cleaning: A Validated Process is Critical for Safety,weblink Valve Magazine, 20 April 2015, en-gb, no,weblink" title="web.archive.org/web/20171115202939weblink">weblink 15 November 2017, dmy-all, BOOK, Raj, Baldev, Jayakumar, T., Thavasimuthu, M., Practical Non-destructive Testing, 2002, Woodhead Publishing, 9781855736009, 10,weblink en, 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.NEWS, New Investigation Finds Some Hotels Don't Wash Sheets Between Guests,weblink House Beautiful, 15 September 2016, en, no,weblink" title="web.archive.org/web/20170703053642weblink">weblink 3 July 2017, dmy-all, NEWS, What's Hiding in Your Hotel Room?,weblink ABC News, 17 November 2010, no,weblink" title="web.archive.org/web/20160722060221weblink">weblink 22 July 2016, dmy-all,

Chemistry

UV/VIS spectroscopy is widely used as a technique in chemistry to analyze chemical structure, the most notable one being conjugated systems. UV radiation is often used to excite a given sample where the fluorescent emission is measured with a spectrofluorometer. In biological research, UV radiation is used for quantification of nucleic acids or proteins.(File:Fluorescent minerals hg.jpg|thumb|right|A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.)Ultraviolet lamps are also used in analyzing minerals and gems.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.N. E. Battikha (ed), The Condensed Handbook of Measurement and Control 3rd Ed. ISA 2007 {{ISBN|1-55617-995-2}}, pp. 65–66 Ultraviolet radiation can detect thin sheens of 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 Raman scattering in water.Mervin Fingas (ed.) Oil Spill Science and Technology Elsevier, 2011 {{ISBN|978-1-85617-943-0}} pp. 123–124

Material science uses

Fire detection

{{see also|Flame detector}}In general, ultraviolet detectors use either a solid-state device, such as one based on silicon carbide or 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 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 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 radiation in the UVC band, whereas the 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 hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.

Photolithography

Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The 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 semiconductors, integrated circuit components,WEB, Deep UV Photoresists,weblinkweblink" title="web.archive.org/web/20060312012823weblink">weblink 2006-03-12, and printed circuit boards. Photolithography processes used to fabricate electronic integrated circuits presently use 193 nm UV and are experimentally using 13.5 nm UV for 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 adhesives are formulated with photoinitiators and resins. When exposed to UV light, polymerization occurs, and so the adhesives harden or cure, usually within a few seconds. Applications include glass and plastic bonding, optical fiber coatings, the coating of flooring, UV coating and paper finishes in offset printing, dental fillings, and decorative fingernail "gels".UV sources for UV curing applications include UV lamps, UV LEDs, and 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 Hg (mercury) or 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 (roughness and hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet.JOURNAL, R. V. Lapshin, A. P. Alekhin, A. G. Kirilenko, S. L. Odintsov, V. A. Krotkov, 2010, Vacuum ultraviolet smoothing of nanometer-scale asperities of poly(methyl methacrylate) surface, Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 4, 1, 1–11, 1027-4510, 10.1134/S1027451010010015,weblink PDF, no,weblink" title="web.archive.org/web/20130909230837weblink">weblink 9 September 2013, dmy-all, UV radiation is useful in preparing low-surface-energy polymers for adhesives. Polymers exposed to UV will oxidize, thus raising the 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 catalytic chemical reaction from 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 formadehyde, 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 nm. Short-wave ultraviolet radiation can destroy DNA in living microorganisms.NEWS,weblink The Importance of UV Light for Plants Cultivated Indoors, 2017-06-11, Best LED Grow Lights Info, 2017-06-24, en-US, UVC's effectiveness is directly related to intensity and exposure time.UV has also been shown to reduce gaseous contaminants such as carbon monoxide and VOCs.JOURNAL, Scott, K.J., Wills, R.R.H., Patterson, B.D., 1971, Journal of the Science of Food and Agriculture, 10.1002/jsfa.2740220916, Removal by ultra-violet lamp of ethylene and other hydrocarbons produced by bananas, 22, 496–7, 9, JOURNAL, Scott, KJ, Wills, RBH, Atmospheric pollutants destroyed in an ultra violet scrubber, 1973, Laboratory Practice, 22, 2, 103–6, 4688707, JOURNAL, Shorter, AJ, Scott, KJ, 1986, Removal of ethylene from air and low oxygen atmospheres with ultra violet radiation, Lebensm-Wiss U Technology, 19, 176–9, UV lamps radiating at 184 and 254 nm can remove low concentrations of hydrocarbons and 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 nm and passed over iron pentaoxide to remove the ozone produced by the UV lamp.

Sterilization and disinfection

File:UV-ontsmetting laminaire-vloeikast.JPG|thumb|right|A low-pressure mercury vapor discharge tube floods the inside of a hood with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.]]Ultraviolet lamps are used to 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 nm being the peak germicidal effectiveness curve. UV at these germicidal wavelengths damage a microorganism's DNA so that it cannot reproduce, making it harmless, (even though the organism may not be killed). 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.JOURNAL, Welch, David, et al, Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases, Scientific Reports, 8, 1, 2752, 10.1038/s41598-018-21058-w, 29426899, 5807439, 2045-2322, January 2018, 2018NatSR...8.2752W, Due to their monochromatic nature (± 5 nm) 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.WEB,weblink Coming Of Age UV-C LED Technology Update, www.wateronline.com, no,weblink 20 April 2017, dmy-all, Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in municipal drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfectionWEB,weblink Solar Water Disinfection, Sodis.ch, 2 April 2011, 2011-11-08, no,weblink" title="web.archive.org/web/20120831050355weblink">weblink 31 August 2012, dmy-all, has been researched for cheaply treating contaminated water using natural 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 pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source.Rulfsorchard.com {{webarchive |url=https://web.archive.org/web/20130616030306weblink |date=16 June 2013 }} The effectiveness of such a process depends on the UV 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 UVWEB,weblink Video Demos, yes,weblink" title="web.archive.org/web/20141219140317weblink">weblink 19 December 2014, dmy-all, 27 November 2014,

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 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.JOURNAL, Silberglied, Robert E., Taylor, Orley R., 1978, Ultraviolet Reflection and Its Behavioral Role in the Courtship of the Sulfur Butterflies Colias eurytheme and C. philodice (Lepidoptera, Pieridae), Behavioral Ecology and Sociobiology, 3, 3, 203–43, 10.1007/bf00296311, In 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.JOURNAL, Meyer-Rochow, V.B., Järvilehto, M., Ultraviolet colours in Pieris napi from northern and southern Finland: Arctic females are the brightest!, Naturwissenschaften, 1997, 84, 4, 165–168, 1997NW.....84..165M, 10.1007/s001140050373, 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 light for collecting beetles in Chaco, ParaguayParaguayThe green fluorescent protein (GFP) is often used in 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 bug zappers 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 collecting nocturnal insects during faunistic survey studies.

Therapy

Ultraviolet radiation is helpful in the treatment of skin conditions such as psoriasis and vitiligo. Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralens is an effective treatment for psoriasis. Due to the potential of psoralens to cause damage to the liver, 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 vitamin A and D derivatives, or systemic treatments such as methotrexate and Soriatane.WEB, UVB Phototherapy,weblinkweblink" title="web.archive.org/web/20070622180124weblink">weblink 22 June 2007, php, 2007-09-23, National Psoriasis Foundation, USA,

Herpetology

Reptiles need UVB for biosynthesis of vitamin D, and other metabolic processes. Specifically cholecalciferol (vitamin D3), which is needed to for basic cellular / neural functioning as well as the utilization calcium for bone and egg production. 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 visual communication between individuals. 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 captive species to survive. Simple supplementation with cholecalciferol (Vitamin D3) will not be enough as there's a complete biosynthetic pathway that is "leapfrogged" (risks of possible overdoses), the intermediate molecules and metabolites also place important functions in the animals health. Natural sunlight in the right levels is always going to be superior to artificial sources, but this might be possible for keepers in different parts of the world.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 were blindness is the result from an improper UVa/b source use and placement photokeratitis. 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. 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. 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.WEB,weblink Vitamin D and Ultraviolet Light – a remarkable process, UV Guide UK, 2017-01-13, no,weblink" title="web.archive.org/web/20160531172209weblink">weblink 31 May 2016, dmy-all,

Evolutionary significance

The evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet radiation. UVB causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy. This leads to frameshifting during genetic replication and protein synthesis, usually killing the cell. Before formation of the UV-blocking ozone layer, when early prokaryotes 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 nucleotide excision repair enzymes. Many enzymes and proteins involved in modern mitosis and 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.BOOK
, Margulis, Lynn, Sagan, Dorion
, yes, Origins of Sex: Three Billion Years of Genetic Recombination
, 1
, Yale University Press
, 1986
,weblink
, 978-0-300-04619-9
, book
,

See also

References

{{Reflist|30em}}

Further reading

  • JOURNAL


, Hu
, S
, Ma
, F
, Collado-Mesa
, F
, Kirsner
, R. S.
, UV radiation, latitude, and melanoma in US Hispanics and blacks
, Arch. Dermatol.
, 140
, 7
, 819–824
, July 2004
, 10.1001/archderm.140.7.819
,
, 15262692,
  • JOURNAL


, Strauss
, CEM
, Funk
, DJ


, Broadly tunable difference-frequency generation of VUV using two-photon resonances in H2 and Kr
, Optics Letters
, 16
, 15
, 1192
, 1991
, 10.1364/ol.16.001192
, 1991OptL...16.1192S
,
  • JOURNAL


, Hockberger
, Philip E.
, A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms
, Photochemistry and Photobiology
, 76
, 6
, 561–569
, 2002
, 10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2
, 12511035,
  • BOOK, Allen, Jeannie, Ultraviolet Radiation: How it Affects Life on Earth,weblink 6 September 2001, Earth Observatory, NASA, USA
,

External links

  • {{Commons category-inline|Ultraviolet light}}
  • {{Wiktionary-inline}}
{{EMSpectrum}}{{Authority control}}

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