8.1 Relevant quantities, their symbols and units

Quantity Symbol Unit(s)
Wavelength λ 1 nanometer = 1 nm = 10-9 m
1 Ångstrøm = 1 Å = 10-10 m
Power P 1 Watt = 1 W
Solid angle Ω 1 steradian = 1 sr
Radiant power or radiant flux Φe 1 Watt = 1 W
Radiant intensity Ie 1 W sr-1
Radiance Le 1 W sr-1 m-2
Irradiance Ee 1 W m-2
Radiant exitance

Me

Ee

1 W m-2

1 W m-2

Luminous flux Φv

1 lumen = 1 lm

photopic: 1 lm corresponds to Φe = 1 / 683 W at λm = 555 nm
skotopic: 1 lm corresponds to Φe = 1 / 1700 W at λ'm = 507 nm

Luminous intensity Iv 1 candela = 1 cd = 1 lm / sr
Luminance Lv 1 lm sr-1 m-2 = 1 cd m-2 = 1 nit
1 stilb = 1 sb = 1 cd m-2
1 apostilb = 1 asb = 1 / π cd m-2
1 lambert = 1 L = 104 / π cd m-2
1 foot-lambert = 1 fl = 3.426 cd m-2
Illuminance Ev 1 lux = 1 lx = 1 lm m-2
1 phot = 1 ph = 104 lx
1 foot-candle = 1 fc = 1 lm ft-2 = 10.764 lx
Luminous exitance

Mv

Ee

1 lm m-2

1 W m-2

Spectral radiant power Φλ(λ) 1 W nm-1
Spectral radiant intensity Iλ(λ) 1 W sr-1 nm-1
Spectral radiance Lλ(λ) 1 W sr-1 m-2 nm-1
Spectral irradiance Eλ(λ) 1 W m-2 nm-1
Spectral radiant exitance

Mλ(λ)

Ee

1 W m-2

1 W m-2

 

Please note: Units in italics are not SI units, not consistent with CIE regulations and should not be used!