Editing Visible spectrum

{{short description|Portion of the electromagnetic spectrum that is visible to the human eye}}
{{Redirect|Color spectrum|the music album|The Color Spectrum}}
[[File:Light dispersion of a mercury-vapor lamp with a flint glass prism IPNr°0125.jpg|thumb|White [[light]] is [[dispersion (optics)|dispersed]] by a glass [[triangular prism (optics)|prism]] into the colors of the visible spectrum.]]

The '''visible spectrum''' is the [[spectral band|band]] of the [[electromagnetic spectrum]] that is [[visual perception|visible]] to the [[human eye]]. [[Electromagnetic radiation]] in this range of [[wavelength]]s is called ''[[visible light]]'' (or simply light).
The '''optical spectrum''' is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the [[ultraviolet]] and [[infrared]] parts of the electromagnetic spectrum as well, known collectively as ''[[optical radiation]]''.<ref>{{cite book |title=Introduction to Optics |isbn=9781108428262 |pages=7–8 |date=December 21, 2017 |publisher=Cambridge University Press |first1=Frank L. |last1=Pedrotti |first2=Leno M. |last2=Pedrotti |first3=Leno S. |last3=Pedrotti}}</ref><ref name="ThoughtCo">{{Cite web |title=What Is the Visible Light Spectrum? |url=https://www.thoughtco.com/the-visible-light-spectrum-2699036 |access-date=2024-10-04 |website=ThoughtCo |language=en |archive-date=2024-09-18 |archive-url=https://web.archive.org/web/20240918221444/https://www.thoughtco.com/the-visible-light-spectrum-2699036 |url-status=live }}</ref>

A typical [[human eye]] will respond to wavelengths from <!--

Before you go and edit this, note that:
* The edges of human vision are not hard cutoffs
* The exact range probably varies from person to person
* The text says "about"
* The text is supported by a reference.

Do you really think whatever number you were about to put in here is somehow more accurate than what is already here? On what basis do you think that?

-->about 380 to about 750 [[nanometers]].<ref>{{cite book | title = Biology: Concepts and Applications | author = Starr, Cecie | publisher = Thomson Brooks/Cole | year = 2005 | isbn = 978-0-534-46226-0 | url = https://archive.org/details/biologyconceptsa06edstar| url-access = registration | page = [https://archive.org/details/biologyconceptsa06edstar/page/94 94] }}</ref> In terms of frequency, this corresponds to a band in the vicinity of 400–790&nbsp;[[Terahertz (unit)|terahertz]]. These boundaries are not sharply defined and may vary per individual.<ref name="Britannica-2024">{{cite web| url= https://www.britannica.com/science/color/The-visible-spectrum| title= The visible spectrum| date= 27 May 2024| publisher= Britannica| access-date= 13 January 2021| archive-date= 12 July 2022| archive-url= https://web.archive.org/web/20220712212209/https://www.britannica.com/science/color/The-visible-spectrum| url-status= live}}</ref> Under optimal conditions, these limits of human perception can extend to 310&nbsp;nm (ultraviolet) and 1100&nbsp;nm (near infrared).<ref>{{cite journal |date=February 2016 |author=D. H. Sliney |pmid=26768917 |pmc=4763133 |issn=1476-5454 |pages=222–229 |journal=Eye |doi=10.1038/eye.2015.252 |issue=2 |title=What is light? The visible spectrum and beyond|volume=30 }}</ref><ref>{{cite book |date=2001 |author=W. C. Livingston |url=https://books.google.com/books?id=4Abp5FdhskAC&pg=PA231 |publisher=Cambridge University Press |isbn=0-521-77284-2 |location=Cambridge, UK |edition=2nd |title=Color and light in nature |access-date=2021-03-05 |archive-date=2024-10-04 |archive-url=https://web.archive.org/web/20241004082506/https://books.google.com/books?id=4Abp5FdhskAC&pg=PA231#v=onepage&q&f=false |url-status=live }}</ref><ref>{{cite journal |date=December 2014 |author=Grazyna Palczewska |display-authors=etal | pages=E5445–E5454 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.1410162111 |number=50 |title=Human infrared vision is triggered by two-photon chromophore isomerization|volume=111 |pmid=25453064 |pmc=4273384 |bibcode=2014PNAS..111E5445P |doi-access=free }}</ref>

The spectrum does not contain all the [[color]]s that the human [[visual system]] can distinguish. ''[[Excitation purity|Unsaturated colors]]'' such as [[pink]], or [[purple]] variations like [[magenta]], for example, are absent because they can only be made from a mix of multiple wavelengths. Colors containing only one wavelength are also called ''pure colors'' or [[spectral color]]s.<ref name="hyperphysics">{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/vision/specol.html#c1 |title=Spectral Colors |work=Hyperphysics |first=R |last=Nave |accessdate=2022-05-11 |archive-date=2017-10-27 |archive-url=https://web.archive.org/web/20171027012933/http://hyperphysics.phy-astr.gsu.edu/hbase/vision/specol.html#c1 |url-status=live }}</ref><ref>{{Cite web |date=2024-09-10 |title=Colour - Visible Spectrum, Wavelengths, Hues {{!}} Britannica |url=https://www.britannica.com/science/color/The-visible-spectrum |access-date=2024-10-04 |website=www.britannica.com |language=en |archive-date=2022-07-12 |archive-url=https://web.archive.org/web/20220712212209/https://www.britannica.com/science/color/The-visible-spectrum |url-status=live }}</ref>

Visible wavelengths pass largely unattenuated through the [[Earth's atmosphere]] via the "[[optical window]]" region of the electromagnetic spectrum. An example of this phenomenon is when clean air [[scattering|scatters]] blue light more than red light, and so the midday sky appears blue (apart from the area around the Sun which appears white because the light is not scattered as much). The optical window is also referred to as the "visible window" because it overlaps the human visible response spectrum. The [[near infrared]] (NIR) window lies just out of the human vision, as well as the medium wavelength infrared (MWIR) window, and the long-wavelength or far-infrared (LWIR or FIR) window, although other animals may perceive them.<ref name="ThoughtCo" /><ref name="Britannica-2024" />

==Spectral colors==
{{Spectral colors simple table}}
{{main|Spectral color}}
Colors that can be produced by visible light of a narrow band of wavelengths ([[monochromatic light]]) are called [[Spectral color|spectral colors]]. The various color ranges indicated in the illustration are an approximation: The spectrum is continuous, with no clear boundaries between one color and the next.<ref>Bruno, Thomas J. and Svoronos, Paris D. N. (2005). ''[https://books.google.com/books?id=FgjHjhCh5wsC&pg=PP1 CRC Handbook of Fundamental Spectroscopic Correlation Charts.] {{Webarchive|url=https://web.archive.org/web/20241004082506/https://books.google.com/books?id=FgjHjhCh5wsC&pg=PP1 |date=2024-10-04 }}'' CRC Press. {{ISBN|9781420037685}}</ref>

==History==
[[File: Newton's color circle.png|thumb|Newton's color circle, from ''Opticks'' of 1704, showing the colors he associated with [[musical note]]s. The spectral colors from red to violet are divided by the notes of the musical scale, starting at D. The circle completes a full [[octave]], from D to D. Newton's circle places red, at one end of the spectrum, next to violet, at the other. This reflects the fact that non-spectral [[purple]] colors are observed when red and violet light are mixed.]]

In the 13th century, [[Roger Bacon]] theorized that [[rainbow]]s were produced by a similar process to the passage of light through glass or crystal.<ref>{{cite book|url=https://archive.org/details/thescienceoflogi01coffuoft|page=[https://archive.org/details/thescienceoflogi01coffuoft/page/185 185]|quote=roger bacon prism.|title=The Science of Logic: An Inquiry Into the Principles of Accurate Thought |first=Peter|last=Coffey|year=1912|publisher=Longmans}}</ref>

In the 17th century, [[Isaac Newton]] discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book ''[[Opticks]]''. He was the first to use the word ''spectrum'' ([[Latin]] for "appearance" or "apparition") in this sense in print in 1671 in describing his [[experiment]]s in [[optics]]. Newton observed that, when a narrow beam of [[sunlight]] strikes the face of a glass [[Dispersive prism|prism]] at an angle, some is [[reflected]] and some of the beam passes into and through the glass, emerging as different-colored bands. Newton hypothesized light to be made up of "corpuscles" (particles) of different colors, with the different colors of light moving at different speeds in transparent matter, red light moving more quickly than violet in glass. The result is that red light is bent ([[refracted]]) less sharply than violet as it passes through the prism, creating a spectrum of colors.

[[File:Newton prismatic colours.JPG|thumb|upright=1.35|Newton's observation of prismatic colors ([[David Brewster]] 1855)]] Newton originally divided the spectrum into six named colors: [[red]], [[Orange (color)|orange]], [[yellow]], [[green]], [[blue]], and [[Violet (color)|violet]]. He later added [[indigo]] as the seventh color since he believed that seven was a perfect number as derived from the [[Ancient Greece|ancient Greek]] [[sophists]], of there being a connection between the colors, the musical notes, the known objects in the [[Solar System]], and the days of the week.<ref name="Isacoff2009">{{cite book|last=Isacoff|first=Stuart|title=Temperament: How Music Became a Battleground for the Great Minds of Western Civilization|url=https://books.google.com/books?id=2kasFeTRcf4C&pg=PA12|access-date=18 March 2014|date=16 January 2009|publisher=Knopf Doubleday Publishing Group|isbn=978-0-307-56051-3|pages=12–13|archive-date=4 October 2024|archive-url=https://web.archive.org/web/20241004082506/https://books.google.com/books?id=2kasFeTRcf4C&pg=PA12#v=onepage&q&f=false|url-status=live}}</ref> The human eye is relatively insensitive to indigo's frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some later commentators, including [[Isaac Asimov]],<ref>{{cite book|last=Asimov|first=Isaac|title=Eyes on the universe : a history of the telescope|year=1975|publisher=Houghton Mifflin|location=Boston|isbn=978-0-395-20716-1|page=[https://archive.org/details/eyesonuniverse00isaa/page/59 59]|url-access=registration|url=https://archive.org/details/eyesonuniverse00isaa/page/59}}</ref> have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet. Evidence indicates that what Newton meant by "indigo" and "blue" does not correspond to the modern meanings of those color words. Comparing Newton's observation of prismatic colors with a color image of the visible light spectrum shows that "indigo" corresponds to what is today called blue, whereas his "blue" corresponds to [[cyan]].<ref>{{cite book|last=Evans|first=Ralph M.|title=The perception of color|year=1974|publisher=Wiley-Interscience|location=New York|isbn=978-0-471-24785-2|edition=null}}</ref><ref>{{cite journal|last=McLaren|first=K.|title=Newton's indigo|journal=Color Research & Application|date=March 2007|volume=10|issue=4|pages=225–229|doi=10.1002/col.5080100411}}</ref><ref>{{cite book|last=Waldman|first=Gary|title=Introduction to light : the physics of light, vision, and color|year=2002|publisher=Dover Publications|location=Mineola|isbn=978-0-486-42118-6|pages=193|url=https://books.google.com/books?id=PbsoAXWbnr4C&q=Newton+color+Indigo&pg=PA193|edition=Dover|access-date=2020-10-29|archive-date=2024-10-04|archive-url=https://web.archive.org/web/20241004082617/https://books.google.com/books?id=PbsoAXWbnr4C&q=Newton+color+Indigo&pg=PA193#v=snippet&q=Newton%20color%20Indigo&f=false|url-status=live}}</ref>

In the 18th century, [[Johann Wolfgang von Goethe]] wrote about optical spectra in his ''[[Theory of Colours]]''. Goethe used the word ''spectrum'' (''Spektrum'') to designate a ghostly optical [[afterimage]], as did [[Schopenhauer]] in ''[[On Vision and Colors]]''. Goethe argued that the continuous spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow and blue-cyan edges with [[white]] between them. The spectrum appears only when these edges are close enough to overlap.

In the early 19th century, the concept of the visible spectrum became more definite, as light outside the visible range was discovered and characterized by [[William Herschel]] ([[infrared]]) and [[Johann Wilhelm Ritter]] ([[ultraviolet]]), [[Thomas Young (scientist)|Thomas Young]], [[Thomas Johann Seebeck]], and others.<ref>{{cite book
 | title = The Cambridge History of Science: The Modern Physical and Mathematical Sciences
 | volume = 5
 | editor = Mary Jo Nye
 | publisher = Cambridge University Press
 | year = 2003
 | isbn = 978-0-521-57199-9
 | page = 278
 | url = https://books.google.com/books?id=B3WvWhJTTX8C&q=spectrum+%22thomas+young%22+herschel+ritter&pg=PA278
 | access-date = 2020-10-29
 | archive-date = 2024-10-04
 | archive-url = https://web.archive.org/web/20241004082507/https://books.google.com/books?id=B3WvWhJTTX8C&q=spectrum+%22thomas+young%22+herschel+ritter&pg=PA278#v=snippet&q=spectrum%20%22thomas%20young%22%20herschel%20ritter&f=false
 | url-status = live
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Young was the first to measure the wavelengths of different colors of light, in 1802.<ref>{{cite book
 | title = Lines of light: the sources of dispersive spectroscopy, 1800–1930
 | author = John C. D. Brand
 | publisher = CRC Press
 | year = 1995
 | isbn = 978-2-88449-163-1
 | pages = 30–32
 | url = https://books.google.com/books?id=sKx0IBC22p4C&q=light+wavelength+color++young+fresnel&pg=PA30
 | access-date = 2020-10-29
 | archive-date = 2024-10-04
 | archive-url = https://web.archive.org/web/20241004082507/https://books.google.com/books?id=sKx0IBC22p4C&q=light+wavelength+color++young+fresnel&pg=PA30#v=snippet&q=light%20wavelength%20color%20%20young%20fresnel&f=false
 | url-status = live
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The connection between the visible spectrum and [[color vision]] was explored by Thomas Young and [[Hermann von Helmholtz]] in the early 19th century. Their [[Young–Helmholtz theory|theory of color vision]] correctly proposed that the eye uses three distinct receptors to perceive color.
{{clear}}

==Limits to visible range==
{{See also|Color vision#Physiology of color perception}}
[[Image:Luminosity.svg|thumb|upright=1.5|[[Photopic vision|Photopic]] (black) and [[scotopic]] (green) luminous efficiency functions. The horizontal axis is wavelength in [[Nanometre|nm]]. See [[luminous efficiency function]] for more info.]]

The visible spectrum is limited to wavelengths that can both reach the retina and trigger [[visual phototransduction]] (excite a [[vertebrate visual opsin|visual opsin]]). Insensitivity to [[UV light]] is generally limited by transmission through the [[Lens (vertebrate anatomy)|lens]]. Insensitivity to [[Infrared|IR light]] is limited by the [[spectral sensitivity]] functions of the visual opsins. The range is defined [[psychometrically]] by the [[luminous efficiency function]], which accounts for all of these factors. In humans, there is a separate function for each of two visual systems, one for [[photopic vision]], used in daylight, which is mediated by [[cone cell]]s, and one for [[scotopic vision]], used in dim light, which is mediated by [[rod cell]]s. Each of these functions have different visible ranges. However, discussion on the visible range generally assumes photopic vision.

===Atmospheric transmission===
The visible range of most animals evolved to match the [[optical window]], which is the range of light that can pass through the atmosphere. The ozone layer absorbs almost all UV light (below 315&nbsp;nm).<ref name="Hunt-2001">{{cite journal |last1=Hunt |first1=D.M. |last2=Wilkie |first2=S.E. |last3=Bowmaker |first3=J.K. |last4=Poopalasundaram |first4=S. |title=Vision in the ultraviolet |journal=Cellular and Molecular Life Sciences |date=October 2001 |volume=58 |issue=11 |pages=1583–1598 |doi=10.1007/PL00000798 |pmid=11706986 |s2cid=22938704 |quote=Radiation below 320 nm [ultraviolet (UV)A] is largely screened out by the ozone layer in the Earth's upper atmosphere and is therefore unavailable to the visual system,|pmc=11337280 }}</ref> However, this only affects cosmic light (e.g. [[sunlight]]), not terrestrial light (e.g. [[Bioluminescence]]).

===Ocular transmission===
[[File:Lens Cornea Transmission.png|thumb|upright=1.5|Cumulative [[absorption spectroscopy|transmission spectra]] of light as it passes through the ocular media, namely after the [[cornea]] (blue), before the [[Lens (vertebrate anatomy)|lens]] (red), after the lens (gray) and before the [[retina]] (orange). The solid lines are for a 4.5 year old eye. The dashed orange line is for a 53 year old eye, and dotted for a 75 year old eye, indicating the effect of lens yellowing.)]]
Before reaching the [[retina]], light must first transmit through the [[cornea]] and [[Lens (vertebrate anatomy)|lens]]. UVB light (<&nbsp;315&nbsp;nm) is filtered mostly by the cornea, and UVA light (315–400&nbsp;nm) is filtered mostly by the lens.<ref name="Boettner-1962">{{cite journal |last1=Boettner |first1=Edward A. |last2=Wolter |first2=J. Reimer |title=Transmission of Ocular Media |journal=Investigative Ophthalmology & Visual Science |date=December 1962 |volume=1 |page=776-783}}</ref> The lens also yellows with age, attenuating transmission most strongly at the blue part of the spectrum.<ref name="Boettner-1962"/> This can cause [[xanthopsia]] as well as a slight truncation of the short-wave (blue) limit of the visible spectrum. Subjects with [[aphakia]] are missing a lens, so UVA light can reach the retina and excite the visual opsins; this expands the visible range and may also lead to [[cyanopsia]].

===Opsin absorption===
Each opsin has a [[spectral sensitivity]] function, which defines how likely it is to absorb a photon of each wavelength. The luminous efficiency function is approximately the superposition of the contributing [[Vertebrate visual opsin|visual opsins]]. Variance in the position of the individual opsin spectral sensitivity functions therefore affects the luminous efficiency function and the visible range. For example, the long-wave (red) limit changes proportionally to the position of the L-opsin. The positions are defined by the peak wavelength (wavelength of highest sensitivity), so as the L-opsin peak wavelength blue shifts by 10&nbsp;nm, the long-wave limit of the visible spectrum also shifts 10&nbsp;nm. Large deviations of the L-opsin peak wavelength lead to a form of [[color blindness]] called [[protanomaly]] and a missing L-opsin ([[protanopia]]) shortens the visible spectrum by about 30&nbsp;nm at the long-wave limit. Forms of color blindness affecting the M-opsin and S-opsin do not significantly affect the luminous efficiency function nor the limits of the visible spectrum.

===Different definitions===
Regardless of actual physical and biological variance, the definition of the limits is not standard and will change depending on the industry. For example, some industries may be concerned with practical limits, so would conservatively report 420–680&nbsp;nm,<ref>{{cite book |last=Laufer |first=Gabriel |chapter=Geometrical Optics |title=Introduction to Optics and Lasers in Engineering |chapter-url=https://books.google.com/books?id=4MxLPYMS5TUC&pg=PA11 |access-date=20 October 2013 |year= 1996 |isbn=978-0-521-45233-5 |page=11|publisher=Cambridge University Press |doi=10.1017/CBO9781139174190.004 |bibcode=1996iole.book.....L }}</ref><ref name="Bradt2004">{{cite book |last=Bradt |first=Hale |title=Astronomy Methods: A Physical Approach to Astronomical Observations |url=https://books.google.com/books?id=hp7vyaGvhLMC&pg=PA26 |access-date=20 October 2013 |year=2004 |publisher=Cambridge University Press |isbn=978-0-521-53551-9 |page=26}}</ref> while others may be concerned with [[psychometrics]] and achieving the broadest spectrum would liberally report 380–750, or even 380–800&nbsp;nm.<ref name="Ohannesian-2001">{{cite book |last1=Ohannesian |first1=Lena |last2=Streeter |first2=Anthony |title=Handbook of Pharmaceutical Analysis |url=https://books.google.com/books?id=DwPb4wgqseYC&pg=PA187 |access-date=20 October 2013 |year=2001 |publisher=CRC Press |isbn=978-0-8247-4194-5 |page=187}}</ref><ref name="Ahluwalia-2000">{{cite book |last1=Ahluwalia |first1=V.K. |last2=Goyal |first2=Madhuri |title=A Textbook of Organic Chemistry |url=https://books.google.com/books?id=tJNJnn0M75MC&pg=PA110 |access-date=20 October 2013 |year= 2000 |publisher=Narosa |isbn=978-81-7319-159-6 |page=110}}</ref> The luminous efficiency function in the [[Near-infrared|NIR]] does not have a hard cutoff, but rather an exponential decay, such that the function's value (or vision sensitivity) at 1,050&nbsp;nm is about 10<sup>9</sup> times weaker than at 700&nbsp;nm; much higher intensity is therefore required to perceive 1,050&nbsp;nm light than 700&nbsp;nm light.<ref name="Sliney-1976">{{cite journal |last1=Sliney |first1=David H. |last2=Wangemann |first2=Robert T. |last3=Franks |first3=James K. |last4=Wolbarsht |first4=Myron L. |year=1976 |title=Visual sensitivity of the eye to infrared laser radiation |journal=[[Journal of the Optical Society of America]] |volume=66 |issue=4 |pages=339–341 |bibcode=1976JOSA...66..339S |doi=10.1364/JOSA.66.000339 |pmid=1262982 |quote=The foveal sensitivity to several near-infrared laser wavelengths was measured. It was found that the eye could respond to radiation at wavelengths at least as far as 1,064 nm. A continuous 1,064 nm laser source appeared red, but a 1,060 nm pulsed laser source appeared green, which suggests the presence of second harmonic generation in the retina.}}</ref>

=== Vision outside the visible spectrum ===
Under ideal laboratory conditions, subjects may perceive infrared light up to at least 1,064&nbsp;nm.<ref name="Sliney-1976" /> While 1,050&nbsp;nm NIR light can evoke red, suggesting direct absorption by the L-opsin, there are also reports that pulsed NIR lasers can evoke green, which suggests [[two-photon absorption]] may be enabling extended NIR sensitivity.<ref name="Sliney-1976" />

Similarly, young subjects may perceive ultraviolet wavelengths down to about 310–313&nbsp;nm,<ref name="Lynch-2001">{{cite book |last1=Lynch |first1=David K. |url=https://books.google.com/books?id=4Abp5FdhskAC&pg=PA231 |title=Color and Light in Nature |last2=Livingston |first2=William Charles |publisher=Cambridge University Press |year=2001 |isbn=978-0-521-77504-5 |edition=2nd |location=Cambridge |page=231 |quote=Limits of the eye's overall range of sensitivity extends from about 310 to 1,050 nanometers |access-date=12 October 2013 |archive-url=https://web.archive.org/web/20221008031821/https://books.google.com/books?id=4Abp5FdhskAC&pg=PA231 |archive-date=8 October 2022 |url-status=live}}</ref><ref name="Dash-2009">{{cite book |last1=Dash |first1=Madhab Chandra |url=https://books.google.com/books?id=7mW4-us4Yg8C&pg=PA213 |title=Fundamentals of Ecology 3E |last2=Dash |first2=Satya Prakash |publisher=Tata McGraw-Hill Education |year=2009 |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. |access-date=18 October 2013 |archive-url=https://web.archive.org/web/20221008031820/https://books.google.com/books?id=7mW4-us4Yg8C&pg=PA213 |archive-date=8 October 2022 |url-status=live}}</ref><ref name="Saidman-1933">{{cite journal |last1=Saidman |first1=Jean |date=15 May 1933 |title=Sur la visibilité de l'ultraviolet jusqu'à la longueur d'onde 3130 |trans-title=The visibility of the ultraviolet to the wave length of 3130 |url=http://visualiseur.bnf.fr/ark:/12148/bpt6k3148d |url-status=live |journal=[[Comptes rendus de l'Académie des sciences]] |language=fr |volume=196 |pages=1537–9 |archive-url=https://web.archive.org/web/20131024092515/http://visualiseur.bnf.fr/ark:/12148/bpt6k3148d |archive-date=24 October 2013 |access-date=21 October 2013}}</ref> but detection of light below 380&nbsp;nm may be due to [[fluorescence]] of the ocular media, rather than direct absorption of UV light by the opsins. As UVA light is absorbed by the ocular media (lens and cornea), it may fluoresce and be released at a lower energy (longer wavelength) that can then be absorbed by the opsins. For example, when the lens absorbs 350&nbsp;nm light, the fluorescence emission spectrum is centered on 440&nbsp;nm.<ref>{{cite book |last1=Kurzel |first1=Richard B. |last2=Wolbarsht |first2=Myron L. |last3=Yamanashi |first3=Bill S. |chapter=Ultraviolet Radiation Effects on the Human Eye |date=1977 |title=Photochemical and Photobiological Reviews |pages=133–167 |doi=10.1007/978-1-4684-2577-2_3|isbn=978-1-4684-2579-6 }}</ref>

===Non-visual light detection===
In addition to the photopic and scotopic systems, humans have other systems for detecting light that do not contribute to the primary [[visual system]]. For example, [[melanopsin]] has an absorption range of 420–540&nbsp;nm and regulates [[circadian rhythm]] and other reflexive processes.<ref name="Enezi-2011">{{cite journal | vauthors = Enezi J, Revell V, Brown T, Wynne J, Schlangen L, Lucas R | title = A "melanopic" spectral efficiency function predicts the sensitivity of melanopsin photoreceptors to polychromatic lights | journal = Journal of Biological Rhythms | volume = 26 | issue = 4 | pages = 314–323 | date = August 2011 | pmid = 21775290 | doi = 10.1177/0748730411409719 | s2cid = 22369861 | doi-access = free }}</ref> Since the melanopsin system does not form images, it is not strictly considered [[Visual perception|vision]] and does not contribute to the visible range.

==In non-humans==
{{See also|Evolution of color vision}}
The visible spectrum is defined as that visible to humans, but the variance between species is large. Not only can [[cone opsin]]s be spectrally shifted to alter the visible range, but [[vertebrate]]s with 4 cones (tetrachromatic) or 2 cones (dichromatic) relative to humans' 3 (trichromatic) will also tend to have a wider or narrower visible spectrum than humans, respectively.

Vertebrates tend to have 1-4 different opsin classes:<ref name="Hunt-2001"/>
* longwave sensitive (LWS) with peak sensitivity between 500–570&nbsp;nm,
* middlewave sensitive (MWS) with peak sensitivity between 480–520&nbsp;nm,
* shortwave sensitive (SWS) with peak sensitivity between 415–470&nbsp;nm, and
* violet/ultraviolet sensitive (VS/UVS) with peak sensitivity between 355–435&nbsp;nm.
Testing the visual systems of animals behaviorally is difficult, so the visible range of animals is usually estimated by comparing the peak wavelengths of opsins with those of typical humans (S-opsin at 420&nbsp;nm and L-opsin at 560&nbsp;nm).

===Mammals===
Most mammals have retained only two opsin classes (LWS and VS), due likely to the [[nocturnal bottleneck]]. However, old world primates (including humans) have since evolved two versions in the LWS class to regain trichromacy.<ref name="Hunt-2001"/> Unlike most mammals, rodents' UVS opsins have remained at shorter wavelengths. Along with their lack of UV filters in the lens, mice have a UVS opsin that can detect down to 340&nbsp;nm. While allowing UV light to reach the retina can lead to retinal damage, the short lifespan of mice compared with other mammals may minimize this disadvantage relative to the advantage of UV vision.<ref>{{cite journal |last1=Gouras |first1=Peter |last2=Ekesten |first2=Bjorn |title=Why do mice have ultra-violet vision? |journal=Experimental Eye Research |date=December 2004 |volume=79 |issue=6 |pages=887–892 |doi=10.1016/j.exer.2004.06.031|pmid=15642326 }}</ref> Dogs have two cone opsins at 429&nbsp;nm and 555&nbsp;nm, so see almost the entire visible spectrum of humans, despite being dichromatic.<ref>{{cite journal |last1=Neitz |first1=Jay |last2=Geist |first2=Timothy |last3=Jacobs |first3=Gerald H. |title=Color vision in the dog |journal=Visual Neuroscience |date=August 1989 |volume=3 |issue=2 |pages=119–125 |doi=10.1017/S0952523800004430|pmid=2487095 |s2cid=23509491 }}</ref> Horses have two cone opsins at 428&nbsp;nm and 539&nbsp;nm, yielding a slightly more truncated red vision.<ref>{{cite journal |last1=Carroll |first1=Joseph |last2=Murphy |first2=Christopher J. |last3=Neitz |first3=Maureen |last4=Ver Hoeve |first4=James N. |last5=Neitz |first5=Jay |title=Photopigment basis for dichromatic color vision in the horse |journal=Journal of Vision |date=3 October 2001 |volume=1 |issue=2 |pages=80–87 |doi=10.1167/1.2.2|pmid=12678603 |doi-access=free |s2cid=8503174 }}</ref>

===Birds===
{{see also|Bird vision#Ultraviolet sensitivity}}
Most other vertebrates (birds, lizards, fish, etc.) have retained their [[tetrachromacy]], including UVS opsins that extend further into the ultraviolet than humans' VS opsin.<ref name="Hunt-2001"/> The sensitivity of avian UVS opsins vary greatly, from 355–425&nbsp;nm, and LWS opsins from 560–570&nbsp;nm.<ref name="Hart-2007">{{cite journal |last1=Hart |first1=Nathan S. |last2=Hunt |first2=David M. |title=Avian Visual Pigments: Characteristics, Spectral Tuning, and Evolution |journal=The American Naturalist |date=January 2007 |volume=169 |issue=S1 |pages=S7–S26 |doi=10.1086/510141|pmid=19426092 |bibcode=2007ANat..169S...7H |s2cid=25779190 |citeseerx=10.1.1.502.4314 }}</ref> This translates to some birds with a visible spectrum on par with humans, and other birds with greatly expanded sensitivity to UV light. The LWS opsin of birds is sometimes reported to have a peak wavelength above 600&nbsp;nm, but this is an effective peak wavelength that incorporates the filter of avian [[oil droplet]]s.<ref name="Hart-2007"/> The peak wavelength of the LWS opsin alone is the better predictor of the long-wave limit. A possible benefit of avian UV vision involves sex-dependent markings on their [[plumage]] that are visible only in the ultraviolet range.<ref>{{cite book|last=Cuthill|first=Innes C |author-link=Innes Cuthill |editor=Peter J.B. Slater|title=Advances in the Study of Behavior|publisher=Academic Press|location=Oxford, England|year=1997|volume=29|chapter=Ultraviolet vision in birds|page=161|isbn=978-0-12-004529-7}}</ref><ref>{{cite book|last=Jamieson|first=Barrie G. M. |title=Reproductive Biology and Phylogeny of Birds|publisher=University of Virginia|location=Charlottesville VA|year=2007|page=128|isbn=978-1-57808-386-2}}</ref>

===Fish===
{{see also|Vision in fish#Ultraviolet}}
[[Teleost]]s (bony fish) are generally tetrachromatic. The sensitivity of fish UVS opsins vary from 347-383 nm, and LWS opsins from 500-570 nm.<ref name="Carleton-2020">{{cite journal |last1=Carleton |first1=Karen L. |last2=Escobar-Camacho |first2=Daniel |last3=Stieb |first3=Sara M. |last4=Cortesi |first4=Fabio |last5=Marshall |first5=N. Justin |title=Seeing the rainbow: mechanisms underlying spectral sensitivity in teleost fishes |journal=Journal of Experimental Biology |date=15 April 2020 |volume=223 |issue=8 |doi=10.1242/jeb.193334|pmid=32327561 |pmc=7188444 |bibcode=2020JExpB.223B3334C }}</ref> However, some fish that use alternative [[chromophore]]s can extend their LWS opsin sensitivity to 625 nm.<ref name="Carleton-2020"/> The popular belief that the common goldfish is the only animal that can see both infrared and ultraviolet light<ref>{{cite web |url=http://www.skeptive.com/disputes/4484 |title=True or False? "The common goldfish is the only animal that can see both infra-red and ultra-violet light." |work= Skeptive |date=2013|access-date=September 28, 2013 |archive-url=https://web.archive.org/web/20131224110616/http://www.skeptive.com/disputes/4484 |archive-date=December 24, 2013 |url-status=usurped |df=mdy-all }}</ref> is incorrect, because goldfish cannot see infrared light.<ref>{{cite book |last=Neumeyer |first=Christa |editor1-first=Olga |editor1-last=Lazareva |editor2-first=Toru |editor2-last=Shimizu |editor3-first=Edward |editor3-last=Wasserman |title= How Animals See the World: Comparative Behavior, Biology, and Evolution of Vision |publisher=Oxford Scholarship Online |year=2012 |chapter=Chapter 2: Color Vision in Goldfish and Other Vertebrates |isbn= 978-0-19-533465-4}}</ref>

===Invertebrates===
The visual systems of invertebrates deviate greatly from vertebrates, so direct comparisons are difficult. However, UV sensitivity has been reported in most insect species.<ref>{{cite journal |last1=Briscoe |first1=Adriana D. |last2=Chittka |first2=Lars |title=The evolution of color vision in insects |journal=Annual Review of Entomology |date=January 2001 |volume=46 |issue=1 |pages=471–510 |doi=10.1146/annurev.ento.46.1.471|pmid=11112177 }}</ref>
[[Bee]]s and many other insects can detect ultraviolet light, which helps them find [[nectar]] in flowers. Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light rather than how colorful they appear to humans. Bees' long-wave limit is at about 590&nbsp;nm.<ref>{{cite journal |last1=Skorupski|first1=Peter|last2=Chittka|first2=Lars|date=10 August 2010 |title=Photoreceptor Spectral Sensitivity in the Bumblebee, ''Bombus impatiens'' (Hymenoptera: Apidae) |journal=PLOS ONE |volume=5 |issue=8 |pages=e12049 |doi=10.1371/journal.pone.0012049 |pmid=20711523|pmc=2919406|bibcode = 2010PLoSO...512049S |doi-access=free}}</ref> [[Mantis shrimp]] exhibit up to 14 opsins, enabling a visible range of less than 300 nm to above 700 nm.<ref name="Hunt-2001"/>

===Thermal vision===
{{main|Infrared sensing in snakes}}
Some snakes can "see"<ref>{{cite journal | pmc = 2693128 | pmid=7256281 | volume=213 | issue=4509 | title=Integration of visual and infrared information in bimodal neurons in the rattlesnake optic tectum | year=1981 | journal=Science | pages=789–91 | last1 = Newman | first1 = EA | last2 = Hartline | first2 = PH | doi=10.1126/science.7256281| bibcode=1981Sci...213..789N }}</ref> radiant heat at [[wavelength]]s between 5 and 30&nbsp;[[μm]] to a degree of accuracy such that a blind [[rattlesnake]] can target vulnerable body parts of the prey at which it strikes,<ref name="Kardong-1991">{{cite journal | last1 = Kardong | first1 = KV | last2 = Mackessy | first2 = SP | year = 1991 | title = The strike behavior of a congenitally blind rattlesnake | journal = Journal of Herpetology | volume = 25 | issue = 2| pages = 208–211 | doi=10.2307/1564650| jstor = 1564650 }}</ref> and other snakes with the organ may detect warm bodies from a meter away.<ref>{{cite journal|doi=10.1038/news.2010.122 |title=Snake infrared detection unravelled |author=Fang, Janet |journal=Nature News|date=14 March 2010 }}</ref> It may also be used in [[thermoregulation]] and [[predator]] detection.<ref name="Krochmal-2004">{{cite journal|last=Krochmal|first=Aaron R.|author2=George S. Bakken |author3=Travis J. LaDuc |title=Heat in evolution's kitchen: evolutionary perspectives on the functions and origin of the facial pit of pitvipers (Viperidae: Crotalinae)|journal=Journal of Experimental Biology |date=15 November 2004|volume=207|pages=4231–4238|doi=10.1242/jeb.01278|pmid=15531644|issue=Pt 24|doi-access=free|bibcode=2004JExpB.207.4231K }}</ref><ref name="Gre92">Greene HW. (1992). "The ecological and behavioral context for pitviper evolution", in Campbell JA, Brodie ED Jr. ''Biology of the Pitvipers''. Texas: Selva. {{ISBN|0-9630537-0-1}}.</ref>

==Spectroscopy==
[[File:Atmospheric electromagnetic opacity.svg|thumb|upright=1.95|[[Earth's atmosphere]] partially or totally [[Opacity (optics)|blocks]] some wavelengths of electromagnetic radiation, but in visible light it is mostly transparent]]
{{main|Spectroscopy}}

[[Spectroscopy]] is the study of objects based on the spectrum of color they emit, absorb or reflect. Visible-light spectroscopy is an important tool in [[astronomy]] (as is [[Astronomical spectroscopy|spectroscopy]] at other wavelengths), where scientists use it to analyze the properties of distant objects. [[Chemical element]]s and small [[molecule]]s can be detected in astronomical objects by observing [[emission line]]s and [[absorption line]]s. For example, [[helium]] was first detected by analysis of the spectrum of the [[Sun]]. The shift in frequency of spectral lines is used to measure the [[Doppler shift]] ([[redshift]] or [[blueshift]]) of distant objects to determine their velocities towards or away from the observer. [[Astronomical spectroscopy]] uses high-dispersion [[diffraction grating]]s to observe spectra at very high spectral resolutions.
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==See also==
{{Wikisource|Littell's Living Age/Volume 145/Issue 1869/Definition of the Color Indigo|Definition of the Color Indigo}}
{{Commons category|Visible spectrum}}
* [[Cosmic ray visual phenomena]]
* [[Electromagnetic absorption by water]]
* [[High-energy visible light]]
* [[Two-photon absorption]] - A method for seeing outside the visible spectrum
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==References==
{{reflist|35em}}
{{EMSpectrum}}
{{Color vision}}
{{Radiation}}
{{Color topics}}

[[Category:Color]]
[[Category:Electromagnetic spectrum]]
[[Category:Optical spectrum| ]]
[[Category:Vision]]