Lux, SI unit of illuminance, symbol lx. Illuminance is the luminous flux (radiant energy per second in the visible part of the spectrum, measured in lumens) per unit area falling on a surface. For a point source of luminous intensity I at a distance d from a surface that is turned away from the source by an angle θ, the illuminance is given by Icos θ /d 2.
Jan 9th, 2015
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