Lambert, Luminance
The lambert (symbol L) is an obsolete unit of luminance named for Johann Heinrich Lambert. A related unit of luminance, the footlambert, is still sometimes used in the lighting industry. The SI units is the candela per square metre (cd/m²). Read more 
Luminance is a photometric measure of the density of luminous intensity in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m
2). The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m
2.
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Photometry