Lighting Design and Simulation Knowledgebase

Lighting Design Glossary

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Photometric brightness is an old and deprecated term for luminance.

(Term of photometry)

The physical measure of brightness.
Luminous intensity per unit projected area of any surface, as measured from a specific direction.

Luminance (usually 'L' in formulas) is the amount of visible light leaving a point on a surface in a given direction. This "surface" can be a physical surface or an imaginary plane, and the light leaving the surface can be due to reflection, transmission, and/or emission

Standard unit of luminance is candela per square meter (cd/m²).
(also called Nits in the USA, from latin "nitere" = "to shine").

There are several older units of luminance:

Apostilb (deprecated) 1 asb  =  1/pi cd/m²
Blondel (deprecated) 1 blondel  =  1/pi cd/m²
Candela per square foot 1 cd/ft²  =  10.764 cd/m²
Candela per square inch 1 cd/in²  =  1550 cd/m²
Footlambert (deprecated) 1 fL  =  3.426 cd/m²
Lambert (deprecated) 1 L  =  104/pi cd/m²
Nit 1 nit  =  1 cd/m²
Skot (deprecated) 1 skot  =  10-3/pi cd/m²
Stilb (deprecated) 1 sb  =  10'000 cd/m²

Typical luminance values are:

 1.6 * 109 cd/m²   Solar disk at noon (don't look!)
600'000 cd/m²   Solar disk at horizon
120'000 cd/m²   Frosted bulb 60 W
11'000 cd/m²   T8 cool white fluorescent
8'000 cd/m²   Average clear sky
2'500 cd/m²   Moon surface
2'000 cd/m²   Average cloudy sky
30 cd/m²   Green electroluminescent source
0.0004 cd/m²   Darkest sky


luminous intensity
English    German
luminance    Die Leuchtdichte
candela per square foot    Die Candela pro Quadratfuß
candela per square inch    Die Candela pro Quadratinch;
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