Editing Visible spectrum (section)

==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.