Lambert

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lambert

A cgs unit of luminance (
or photometric brightness) equal to one lumen, or 1/π candela per square centimeter.

This luminance is produce by a blackbody source of luminous intensity 1 candela at a distance of 1 centimeter. The corresponding SI (or mks) unit is the apostilb, a unit 104 smaller produced by 1 candela at a distance of 1 m. The sun's disk at zenith at sea level under clear skies has a luminance of about 470 000 lambert, while that of a 60-watt, inside-frosted, tungsten-filament light bulb is about 38 lambert.

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