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Photonics Handbook

Photometric Units


Photometric Units


SI Units

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



Non-SI Units

                                                                  Luminous Intensity
                                                                  candlepower = the candela
                                                                
                                                                  Luminance
                                                                  1 stilb = 1 cd/cm2 = 10,000 cd/m2
                                                                  1 apostilb = (1/π) cd/m2 = 0.3183 cd/m2
                                                                  1 lambert = (10,000/π) cd/m2 = 3183 cd/m2
                                                                  1 millilambert = 0.001 lambert = 3.183 cd/m2
                                                                  1 footlambert = (1/π) 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.
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