Illuminance 773153 218731286 2008-06-11T22:31:48Z TXiKiBoT 3171782 robot Adding: [[be-x-old:Асьветленасьць]] [[Image:Lux meter.jpg|thumb|right|A lux meter for measuring illuminances in work environments.]] In [[photometry (optics)|photometry]], '''illuminance''' is the total [[luminous flux]] incident on a surface, per unit [[area]]. It is a measure of the intensity of the incident [[light]], wavelength-weighted by the [[luminosity function]] to correlate with human brightness perception. Similarly, '''luminous emittance''' is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as '''luminous exitance'''. In [[SI]] [[SI derived units|derived units]], these are both measured in [[lux]] (lx) or [[lumen (unit)|lumens]] per [[square metre]] (cd&middot;sr&middot;m<sup>−2</sup>). In the [[CGS]] system, the unit of illuminance is the [[phot]]. One phot is equal to 10,000 lux. The [[foot-candle]] is a non-metric unit of illuminance that is used in [[photography]]. Illuminance was formerly often called [[brightness]], but this leads to confusion with other uses of the word. "Brightness" should never be used for quantitative description, but only for nonquantitative references to physiological sensations and perceptions of light. The human eye is capable of seeing somewhat more than a 2 trillion-fold range: The presence of white objects is somewhat discernible under starlight, at 5×10<sup>−5</sup> lux, while at the bright end, it is possible to read large text at 10<sup>8</sup> lux, or about 1,000 times that of direct [[sunlight]], although this can be very uncomfortable and cause long-lasting [[afterimages]]. ==See also== *[[Irradiance]] *[[Exposure_value#EV_as_a_measure_of_luminance_and_illuminance|Exposure value]] {{SI_light_units}} == References == * Knowledgedoor, LLC (2005). [http://www.knowledgedoor.com/1/Library_of_Units_and_Constants/Quantity_Index/illuminance.htm Library of Units and Constants: Illuminance Quantity]. Retrieved [[2006-07-21]]. * [http://www.convertthis.com/converters/illuminance.aspx Illuminance Converter]. Retrieved [[2006-07-21]]. == 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]. <!--Categories--> [[Category:Physical quantity]] [[Category:Photometry]] [[be-x-old:Асьветленасьць]] [[bg:Осветеност]] [[cs:Osvětlenost]] [[de:Beleuchtungsstärke]] [[es:Iluminancia]] [[fr:Éclairement lumineux]] [[ko:조도]] [[is:Lýsing]] [[lv:Virsmas apgaismojums]] [[lt:Apšvieta]] [[nl:Illuminantie]] [[ja:照度]] [[pl:Natężenie oświetlenia]] [[ru:Освещённость]] [[fi:Valaistusvoimakkuus]] [[uk:Освітленість]]