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Light Measurement - Useful Formulae

Light Measurement Formulae

The table below provides a list of useful formulae used in photometry and colorimetry.

Parameter

Equation

Notes

CIE (1931) Chromaticity Coordinates

 

1931 2° observer 

 

 

 

CIE (1976) Chromaticity Coordinates

 

1964 10° observer 

 

 

 

Illuminance

 

E = illuminance (lx)
Fv = luminous flux (lm)
A = area (m2

 

E = illuminance (lx)
I = luminous intensity (cd)
r = distance (m)
(Applies to the far-field)

Inverse Squared Law

E = illuminance (lx)
x = distance (m)
(Applies to the far-field)

Luminance

L = luminance (cd/m2)
E = illuminance (lx)
p = reflectance 

Luminous Exitance

M = luminous exitance (lm/m2)
Fv = luminous flux (lm)
A = area (m2)

 

 M = luminous exitance (lm/m2)
E = illuminance (lx)
p = reflectance

Luminous Intensity

I = luminous intensity (cd)
 Fv = luminous flux (lm)
W = solid angle (sr-1)

 

 I = luminous intensity (cd)
E = illuminance (lx)
A = area (m2)
W = solid angle (sr-1)
r = distance (m)

Solid Angle

 W = solid angle (sr-1)
A = spherical surface area (m2)
r = radius of sphere (m)

 

 W = solid angle (sr-1)
a = planar angle (°)
(This is an approximation)

Wave Number

l = wavelength (µm)

» Back - Guide to Units

» Next - Glossary of Terms

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