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Luminance

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

 

References:
   brightness
light
luminous intensity
photometry
 
 
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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