Luminous Power Per Unit Area of Surface
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Examples of common illuminance levels from Wikipedia at right. |
Include surface angle |
HyperPhysics***** Light and Vision | R Nave |
LuxThe lux is defined as a lumen per square meter and is a unit of illuminance. An equivalent term is luminous flux density. As such, it measures the amount of visible light striking a surface. The standard symbol for it is Ev. It must take into account the sensitivity of the eye for the wavelengths of light involved, but that is taken care of in establishing the number of lumens.
Most light meters measure this quantity, and it is the quantity most commonly used to state requirements for architectural lighting. Suggested illuminance levels from nzdl |
Index Photometry concepts Vision concepts Reference: Williamson & Cummins | ||
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NitThe nit is the unit of luminance and is defined as a candela per square meter. The unit could be written as cd/m2 or lm/m2sr. It is most often used to characterize the "brightness" of flat emitting or reflecting surfaces. Palmer gives the following examples: laptop computer screens 100 to 250 nits, while those which are sunlight-readable must have more than 1000 nits. Typical CRT monitors are said to have luminances of 50-125 nits. The standard symbol for the luminance in nits is Lv. |
Index Photometry concepts Vision concepts Reference: Williamson & Cummins | ||
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