# Luminance

Luminance

Luminance is a photometric measure of the density of luminous intensity in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2). The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2.

Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much luminous power will be perceived by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil. Luminance is used in the video industry to characterize the brightness of displays. In this industry, one candela per square metre is commonly called a "nit". A typical computer display emits between 50 and 300 nits.

Luminance is invariant in geometric optics. This means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the output luminance is "at most" equal to the input. As an example, if you form a demagnified image with a lens, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be "brighter" than the source.

Definition

Luminance is defined by:$L_v = frac\left\{d^2 F\right\}\left\{dA,d\left\{Omega\right\} cos heta\right\}$

where:$L_v$ is the luminance (cd/m2),:$F$ is the luminous flux or luminous power (lm),:$heta,$ is the angle between the surface normal and the specified direction,:$A$ is the area of the surface (m2), and:$Omega,$ is the solid angle (sr).

ee also

*Diffuse reflection
*Etendue
*Illuminance
*Lambert
*Lambertian reflectance
*Lightness, property of a color
*Luma, the representation of luminance in a video monitor
*Exposure value

* A Kodak guide to [http://www.kodak.com/cluster/global/en/consumer/products/techInfo/am105/am105kic.shtml Estimating Luminance and Illuminance] using a camera's exposure meter. Also available in [http://www.kodak.com/cluster/global/en/consumer/products/techInfo/am105/am105kic.pdf PDF form] .

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### Look at other dictionaries:

• luminance — [ lyminɑ̃s ] n. f. • 1948; du rad. de lumineux ♦ Phys. Quotient de l intensité lumineuse d une surface par l aire apparente de cette surface pour un observateur lointain (exprimé en candela par mètre carré). ⇒ brillance. ● luminance nom féminin… …   Encyclopédie Universelle

• luminance — luminousness, 1862, from L. luminantem (nom. luminans), prp. of luminare (see LUMINARY (Cf. luminary)) …   Etymology dictionary

• luminance — [lo͞o′mə nəns] n. [< L lumen (gen. luminis), LIGHT1 + ANCE] 1. the quality or state of being luminous 2. a measure of the brightness of a luminous surface, measured in candelas per unit area …   English World dictionary

• Luminance — En physique, la luminance est l intensité d une source étendue dans une direction donnée, divisée par l aire apparente de cette source dans cette même direction. Ne pas confondre la luminance tout court, qui est une grandeur photométrique… …   Wikipédia en Français

• luminance — skaistis statusas T sritis Standartizacija ir metrologija apibrėžtis Paviršiaus elemento šviesos pasirinktąja kryptimi stipris, padalytas iš statmenosios to elemento projekcijos į statmeną pasirinktajai krypčiai plokštumą ploto. Matavimo vienetas …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• luminance — skaistis statusas T sritis fizika atitikmenys: angl. brightness; luminance; luminosity vok. Helligkeit, f; Leuchtdichte, f rus. яркость, f pranc. brillance, f; luminance, f …   Fizikos terminų žodynas

• luminance — /looh meuh neuhns/, n. 1. the state or quality of being luminous. 2. Also called luminosity. the quality or condition of radiating or reflecting light: the blinding luminance of the sun. 3. Optics. the quantitative measure of brightness of a… …   Universalium

• luminance — lu•mi•nance [[t]ˈlu mə nəns[/t]] n. 1) the state or quality of being luminous 2) the quality or condition of radiating or reflecting light: the blinding luminance of the sun[/ex] 3) opt the quantitative measure of brightness of a light source or… …   From formal English to slang

• Luminance — A&V The measurable, luminous intensity of a video signal. Differentiated from brightness in that the latter is nonrneasurable and sensory. The color video picture information contains two components: luminance (brightness and contrast) and… …   Audio and video glossary

• luminance — skaistis statusas T sritis chemija apibrėžtis Šviečiančio ar šviesą sklaidančio paviršiaus šviesos ryškumas tam tikra kryptimi (Cd/m²). atitikmenys: angl. brightness; luminance; luminosity rus. яркость …   Chemijos terminų aiškinamasis žodynas