Editing Ultraviolet (section)

{{Short description|Energetic, invisible radiant energy range}}
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| image1            = UV-handlamp hg.jpg
| caption1          = Portable ultraviolet lamp (UVA and UVB)
| image2            = Pipefitter welder kutzo.jpg
| caption2          = UV radiation is also produced by [[electric arc]]s. [[Arc welder]]s must wear [[eye protection]] and cover their skin to prevent [[photokeratitis]] and serious [[sunburn]].
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'''Ultraviolet radiation''', also known as simply '''UV''', is [[electromagnetic radiation]] of [[wavelength]]s of 10–400 [[Nanometre|nanometers]], shorter than that of [[visible light]], but longer than [[X-ray]]s. UV [[radiation]] is present in [[sunlight]] and constitutes about 10% of the total [[Electromagnetism|electromagnetic]] radiation output from the Sun. It is also produced by [[electric arc]]s, [[Cherenkov radiation]], and specialized lights, such as [[mercury-vapor lamp]]s, [[tanning lamp]]s, and [[black light]]s.

The [[photon]]s of ultraviolet have greater energy than those of visible light, from about 3.1&nbsp;to&nbsp;12&nbsp;[[electron volt]]s, around the minimum energy required to [[ionize]] [[atom]]s.<ref name="Maqbool" />{{rp|25-26}}  Although long-wavelength ultraviolet is not considered an [[ionizing radiation]]<ref name="Ida">{{cite book
  | last = Ida
  | first = Nathan 
  | title = Engineering Electromagnetics, 2nd Ed.
  | publisher = Springer Science and Business Media
  | date = 2008
  | pages = 1122
  | language = 
  | url = https://books.google.com/books?id=2CbvXE4o5swC&dq=ultraviolet+ionizing+non-ionizing+&pg=PA1122
  | archive-url= 
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  | isbn = 9780387201566
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  | jfm =}}</ref> because its [[photon]]s lack sufficient energy, it can induce [[chemical reaction]]s and cause many substances to glow or [[fluoresce]]. Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. These interactions can involve exciting orbital electrons to higher energy states in molecules potentially breaking chemical bonds. In contrast, the main effect of longer wavelength radiation is to excite vibrational or rotational states of these molecules, increasing their temperature.<ref name="Maqbool">{{cite book
  | last = Maqbool
  | first = Muhammad 
  | title = An Introduction to Non-Ionizing Radiation
  | publisher = Bentham Science Publishers
  | date = 2023
  | location = 
  | language = 
  | url = https://books.google.com/books?id=ZyHkEAAAQBAJ&pg=PA28
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  | jfm =}}</ref>{{rp|28}}  Short-wave ultraviolet light is [[ionizing radiation]].<ref name="Ida" /> Consequently, short-wave UV damages [[DNA]] and sterilizes surfaces with which it comes into contact.

For humans, [[Sun tanning|suntan]] and [[sunburn]] are familiar effects of exposure of the skin to UV, along with an increased risk of [[skin cancer]]. The amount of UV radiation 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 [[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, UV (specifically, UVB) is also responsible for the formation of [[vitamin D]] in most land [[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 detrimental to life.

The lower wavelength limit of the [[visible spectrum]] is conventionally taken as 400&nbsp;nm.  Although ultraviolet rays are not generally [[human vision|visible to humans]], 400&nbsp;nm is not a sharp cutoff, with shorter and shorter wavelengths becoming less and less visible in this range.<ref name='hambling'/>  Insects, birds, and some mammals can see near-UV (NUV), i.e., somewhat 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 |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 |doi-access=free |bibcode=2016JExpB.219.2790C |hdl-access=free }}</ref>
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