Editing Luminous efficiency function (section)

{{Short description|Description of the average spectral sensitivity of human visual perception of brightness}}
{{For|the luminosity function in astronomy|Luminosity function (astronomy)}}
[[Image:Luminosity.svg|thumb|right|400px|[[Photopic vision|Photopic]] (black) and [[scotopic vision|scotopic]] (green) luminous efficiency functions.<ref name="scvl" group=c/> The photopic includes the CIE 1931 standard<ref name="ciexyz31" group=c/> (solid), the Judd–Vos 1978 modified data<ref name="vljv" group=c/> (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data<ref name="ssvl2" group=c/> (dotted). The horizontal axis is wavelength in [[Nanometre|nm]].]]
A '''luminous efficiency function''' or '''luminosity function''' represents the average [[spectral sensitivity]] of human [[visual perception]] of [[light]]. It is based on subjective judgements of which of a pair of different-colored lights is brighter, to describe relative sensitivity to light of different [[wavelength]]s.  It is not an absolute reference to any particular individual, but is a standard observer representation of visual sensitivity of a theoretical [[human eye]]. It is valuable as a baseline for experimental purposes, and in [[colorimetry]].  Different luminous efficiency functions apply under different lighting conditions, varying from [[photopic]] in brightly lit conditions through [[mesopic]] to [[scotopic]] under low lighting conditions.  When not specified, ''the luminous efficiency function'' generally refers to the photopic luminous efficiency function.

The CIE photopic luminous efficiency function {{math|{{overline|''y''}}(λ)}} or {{math|''V''(λ)}} is a standard function established by the [[Commission Internationale de l'Éclairage]] (CIE) and standardized in collaboration with the [[International Organization for Standardization|ISO]], <ref>{{cite book | url=https://www.iso.org/standard/83178.html | title=ISO/CIE 23539:2023 CIE TC 2-93 Photometry — The CIE system of physical photometry | publisher=ISO/CIE | date=2023 | language=en | doi=10.25039/IS0.CIE.23539.2023}}</ref> and may be used to convert [[radiant energy]] into luminous (i.e., visible) energy.  It also forms the central [[CIE 1931 color space#Color matching functions|color matching function]] in the [[CIE 1931 color space]].