- Illuminance
In photometry, illuminance is the total
luminous flux incident on a surface, per unitarea . It is a measure of the intensity of the incidentlight , wavelength-weighted by theluminosity 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 derived units, these are both measured inlux (lx) or lumens persquare metre (cd·sr·m−2). In theCGS system, the unit of illuminance is thephot . One phot is equal to 10,000 lux. Thefoot-candle is a non-metric unit of illuminance that is used inphotography .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 5×10−5 lux, while at the bright end, it is possible to read large text at 108 lux, or about 1,000 times that of direct
sunlight , although this can be very uncomfortable and cause long-lastingafterimages .Fact|date=July 2008ee also
*
Irradiance
*Exposure valueReferences
* 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] . Retrieved2006-07-21 .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] .
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