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Photonics HandbookGeneral Reference

Photometric Units

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Photometric Units


SI Units


Quantity
Unit
 
Luminous flux
lumen    lm
 
Luminous intensity
candela    cd
 
Luminance
cd/m2
 
lm/m2    lx
 


Non-SI Units


Luminous Intensity
candlepower = the candela

Luminance
1 stilb = 1 cd/cm2 = 10,000 cd/m2
1 apostilb = (1/p) cd/m2 = 0.3183 cd/m2
1 lambert = (10,000/p) cd/m2 = 3183 cd/m2
1 millilambert = 0.001 lambert = 3.183 cd/m2
1 footlambert = (1/p) cd/ft2 = 3.426 cd/m2
1 candela/ft2 = 10.76 cd/m2
1 candela/in.2 = 1550 cd/m2

Illuminance
1 footcandle = 1 lm/ft2 = 10.76 lm/m2 or lx


Glossary
illuminance
Luminous flux incident per unit area of a surface; luminous incidence. (The use of the term "illumination" for this quantity conflicts with its more general meaning.)
intensity
Flux per unit solid angle.
illuminanceintensityphotometric unitsGeneral Reference

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