Editing Tapetum lucidum (section)

==Function and mechanism==
[[Image:Calf-Eye-Posterior-With-Retina-Detached-2005-Oct-13.jpg|thumb|Choroid dissected from a calf's eye, tapetum lucidum appearing iridescent blue]]

The presence of a tapetum lucidum enables animals to see in dimmer light than would otherwise be possible. The tapetum lucidum, which is [[iridescent]], reflects light roughly on the [[Interference (wave propagation)|interference]] principles of [[thin-film optics]], as seen in other iridescent tissues. However, the tapetum lucidum cells are [[Chromatophore#Iridophores and leucophores|leucophore]]s, not [[Chromatophore#Iridophores and leucophores|iridophore]]s.{{dubious|date=January 2021|reason=Then why is the tapetum lucidum colored?}}

The tapetum functions as a [[retroreflector]] which reflects light directly back along the light path. This serves to match the original and reflected light, thus maintaining the sharpness and contrast of the image on the retina. The tapetum lucidum reflects with [[Interference (wave propagation)|constructive interference]],<ref name="Locket1974"/> thus increasing the quantity of light passing through the retina. In the cat, the tapetum lucidum increases the sensitivity of vision by 44%, allowing the cat to see light that is imperceptible to human eyes.<ref>{{cite journal |vauthors=Gunter R, Harding HG, Stiles WS |title=Spectral reflexion factor of the cat's tapetum |journal=Nature |volume=168 |issue=4268 |pages=293–4 |date=August 1951 |pmid=14875072 |doi= 10.1038/168293a0|bibcode=1951Natur.168..293G |s2cid=4166491 }}</ref> When a tapetum lucidum is present, its location on the eyeball varies with the placement of the eyeball in the head.<ref name="Lee1886">{{cite journal |last=Lee |first=Henry |year=1886 |title=On the ''Tapetum Lucidum'' |journal=Med Chir Trans |volume=69 |pages=239–245 |doi=10.1177/095952878606900113 |pmc=2121549 |pmid=20896672}}</ref>

Apart from its eyeshine, the tapetum lucidum itself has a color. It is often described as iridescent. In [[tiger]]s, it is greenish.<ref>Fayrer, Sir Joseph (1889) ''The deadly wild beasts of India'', pp. 218–240 in James Knowls (ed) ''The Nineteenth Century'', Henry S. King & Co., v. 26; p. 219. [https://books.google.com/books?id=kTMAAAAAYAAJ via Google Books]</ref> In [[ruminant]]s, it may be golden green with a blue periphery,<ref name="Charnock1896" /> or whitish or pale blue with a lavender periphery. In [[dog]]s, it may be whitish with a blue periphery.<ref name="Charnock1896" /> The color in [[reindeer]] changes seasonally, allowing the animals to better avoid predators in low-light winter at the price of blurrier vision.<ref>{{cite journal |doi=10.1098/rspb.2013.2451 |title=Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer |author1=Karl-Arne Stokkan |author2=Lars Folkow |author3=Juliet Dukes |author4=Magella Neveu |author5=Chris Hogg |author6= Sandra Siefken |author7=Steven C. Dakin |author8=Glen Jeffery |date=22 December 2013 |journal=Proceedings of the Royal Society B|volume=280 |issue=1773 |pmid=24174115 |pmc=3826237 }}</ref>