Luminance 18365 222833609 2008-07-01T09:59:25Z JAnDbot 1725149 robot Removing: [[sv:Luminans]] {{Otheruses}} '''Luminance''' is a [[Photometry (optics)|photometric]] measure of the [[density (disambiguation)|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/m<sup>2</sup>). The [[CGS]] unit of luminance is the stilb, which is equal to one candela per square centimetre or 10&nbsp;kcd/m<sup>2</sup>. Luminance is often used to characterize emission or reflection from flat, [[diffuse reflection|diffuse]] surfaces. The luminance indicates how much [[luminous flux|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 [[brightness|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_(unit)|nit]]". A typical computer display emits between 50 and 300 nits. Luminance is [[Invariant (physics)|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 :<math>L_v = \frac{d^2 F}{dA\,d{\Omega} \cos \theta}</math> where :<math>L_v</math> is the luminance ([[candela|cd]]/[[square metre|m<sup>2</sup>]]), :<math>F</math> is the [[luminous flux]] or luminous power ([[lumen (unit)|lm]]), :<math>\theta\,</math> is the [[angle]] between the [[surface normal]] and the specified direction, :<math>A</math> is the [[area]] of the surface ([[square metre|m<sup>2</sup>]]), and :<math>\Omega\,</math> is the [[solid angle]] ([[Steradian|sr]]). ==See also== *[[Diffuse reflection]] *[[Etendue]] *[[Illuminance]] *[[Lambert (unit)|Lambert]] *[[Lambertian reflectance]] *[[Lightness_(color)|Lightness]], property of a color *[[Radiance]] *[[Exposure_value#EV_as_a_measure_of_luminance_and_illuminance|Exposure value]] == External links == * 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]. {{SI light units}} [[Category:Photometry]] [[Category:Physical quantity]] [[cs:Jas]] [[de:Leuchtdichte]] [[et:Heledus]] [[es:Luminancia]] [[fr:Luminance]] [[ko:휘도]] [[nl:Luminantie]] [[ja:輝度 (光学)]] [[pl:Luminacja]] [[ru:Яркость]] [[fi:Luminanssi]] [[uk:Яскравість]]