Editing Light (section)

{{Short description|Electromagnetic radiation humans can see}}
{{Other uses}}
{{Redirect|Visible light}}
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{{Use dmy dates|date=September 2019}}

[[File:Prism flat rainbow (cropped).jpg|thumb|upright=1.3|A triangular [[dispersive prism|prism]] [[dispersion (optics)|dispersing]] a beam of white light. The longer wavelengths (red) and the shorter wavelengths (green-blue) are separated.]]
{{Modern physics}}

'''Light''', '''visible light''', or '''visible radiation''' is [[electromagnetic radiation]] that can be [[visual perception|perceived]] by the [[human eye]].<ref>[[International Commission on Illumination|CIE]] (1987). [http://www.cie.co.at/publ/abst/17-4-89.html ''International Lighting Vocabulary''] {{Webarchive|url=https://web.archive.org/web/20100227034508/http://www.cie.co.at/publ/abst/17-4-89.html |date=27 February 2010 }}. Number 17.4. CIE, 4th ed.. {{ISBN|978-3-900734-07-7}}.<br />By the ''International Lighting Vocabulary'', the definition of ''light'' is: "Any radiation capable of causing a visual sensation directly."</ref> Visible light spans the [[visible spectrum]] and is usually defined as having [[wavelength]]s in the range of 400–700 [[nanometre]]s (nm), corresponding to [[frequency|frequencies]] of 750–420 [[terahertz (unit)|terahertz]]. The visible band sits adjacent to the [[infrared]] (with longer wavelengths and lower frequencies) and the [[ultraviolet]] (with shorter wavelengths and higher frequencies), called collectively ''[[optical radiation]]''.<ref name="Pal2001">{{cite book |last1=Pal |first1=G.K. |last2=Pal |first2=Pravati |title=Textbook of Practical Physiology |chapter-url=https://books.google.com/books?id=CcJvIiesqp8C&pg=PA387 |access-date=11 October 2013 |edition=1st |year=2001 |publisher=Orient Blackswan |location=Chennai |isbn=978-81-250-2021-9 |page=387 |chapter=chapter 52 |quote=The human eye has the ability to respond to all the wavelengths of light from 400–700 nm. This is called the visible part of the spectrum. |archive-date=8 October 2022 |archive-url=https://web.archive.org/web/20221008031819/https://books.google.com/books?id=CcJvIiesqp8C&pg=PA387 |url-status=live }}</ref><ref name="BuserImbert1992">{{cite book |last1=Buser |first1=Pierre A. |last2=Imbert |first2=Michel |title=Vision |url=https://archive.org/details/vision0000buse |url-access=registration |access-date=11 October 2013 |year=1992 |publisher=MIT Press |isbn=978-0-262-02336-8 |page=[https://archive.org/details/vision0000buse/page/50 50] |quote=Light is a special class of radiant energy embracing wavelengths between 400 and 700 nm (or mμ), or 4000 to 7000 Å.}}</ref>

In [[physics]], the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not.<ref>{{Cite book |title=Camera lenses: from box camera to digital |author=Gregory Hallock Smith |publisher=SPIE Press |year=2006 |isbn=978-0-8194-6093-6 |page=4 |url=https://books.google.com/books?id=6mb0C0cFCEYC&pg=PA4 |access-date=15 November 2020 |archive-date=8 October 2022 |archive-url=https://web.archive.org/web/20221008031820/https://books.google.com/books?id=6mb0C0cFCEYC&pg=PA4 |url-status=live }}</ref><ref>{{Cite book |title=Comprehensive Physics XII |author=Narinder Kumar |publisher=Laxmi Publications |year=2008 |isbn=978-81-7008-592-8 |page=1416 |url=https://books.google.com/books?id=IryMtwHHngIC&pg=PA1416}}</ref> In this sense, [[gamma ray]]s, [[X-ray]]s, [[microwave]]s and [[radio wave]]s are also light. The primary properties of light are [[intensity (physics)|intensity]], propagation direction, frequency or wavelength [[spectrum]], and [[polarization (waves)|polarization]]. Its [[speed of light|speed in vacuum]], {{val|299792458|u=m/s}}, is one of the fundamental [[physical constant|constants]] of nature.<ref name="LeClerq">{{Cite book |last1=Uzan |first1=J-P |last2=Leclercq |first2=B |year=2008 |title=The Natural Laws of the Universe: Understanding Fundamental Constants |url=https://archive.org/details/the-natural-laws-of-the-universe-understanding-fundamental-constants |pages=43–44 |translator=Robert Mizon|isbn=978-0-387-73454-5|bibcode=2008nlu..book.....U |publisher=[[Springer-Praxis]], [[Internet Archive]]: 2020-06-14 AbdzexK uban|doi=10.1007/978-0-387-74081-2 |doi-broken-date=1 November 2024 }}</ref> All electromagnetic radiation exhibits some properties of both [[wave–particle duality|particles and waves]]. Single, massless elementary particles, or [[quantum|quanta]], of light called ''[[photon]]s'' can be detected with specialized equipment; phenomena like interference are described by waves. Most everyday interactions with light can be understood using [[geometrical optics]]; [[quantum optics]], is an important research area in [[modern physics]].

The main source of natural light on Earth is the [[Sun]]. Historically, another important source of light for humans has been [[fire]], from ancient campfires to modern [[kerosene lamp]]s. With the development of [[electric light]]s and [[history of electric power transmission|power systems]], electric lighting has effectively replaced firelight.