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:
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Apostilb (deprecated)
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1 asb | = |
1/pi cd/m2
|
|
Blondel (deprecated)
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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)
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1 fL | = |
3.426 cd/m2
|
|
Lambert (deprecated)
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1 L | = |
104/pi cd/m2
|
|
Nit
|
1 nit | = |
1 cd/m2
|
|
Skot (deprecated)
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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
|
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