Editing Luminance (section)

{{Short description|Photometric measure}}
{{Distinguish|Luma (video)|Luminescence|Illuminance}}
{{Other uses}}
{{More citations needed|date=April 2023}}
[[File:TealightLuminanceImage.jpg|thumb|A [[tea light]]-type candle, imaged with a luminance camera; [[false color]]s indicate luminance levels per the bar on the right (cd/m<sup>2</sup>)]]
'''Luminance''' is a [[Photometry (optics)|photometric]] measure of the [[luminous intensity]] per [[units of measurement|unit area]] of [[light]] travelling in a given direction.<ref>{{cite encyclopedia | title=luminance, 17-21-050 | encyclopedia=CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition. | publisher=CIE - International Commission on Illumination | accessdate=20 April 2023 | year=2020 | url=https://cie.co.at/eilvterm/17-21-050}}</ref> It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given [[solid angle]].

The procedure for conversion from spectral [[radiance]] to luminance is standardized by the [[International Commission on Illumination|CIE]] and [[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>

[[Brightness]] is the [[terminology|term]] for the ''subjective'' impression of the ''objective'' luminance measurement standard (see {{Section link|Objectivity (science)|Objectivity in measurement}} for the importance of this contrast).

The [[SI base unit|SI unit]] for luminance is [[candela per square metre]] (cd/m<sup>2</sup>). A non-SI term for the same unit is the [[nit (unit)|nit]]. The unit in the [[Centimetre–gram–second system of units|Centimetre–gram–second system of units (CGS)]] (which predated the SI system) is the [[stilb (luminance)|stilb]], which is equal to one candela per square centimetre or 10&nbsp;kcd/m<sup>2</sup>.