Radiant Quantities and Units

SI Unit(s)

Symbol

Flux

W, i.e. J/s

Φ

Intensity

W/sr

I

Exitance

W/m2

M

Irradiance

W/m2

E

Radiance

W/sr/m2

L

  • A prefix of “spectral” modifies the unit such that it is per wavelength or wavenumber.

  • Exitance and irradiance have the same units, but one refers to radiation exiting a surface and the other to radiation incident upon a surface.

  • A common unit for spectral radiance is the μFlick. 1 μFlick = 1 μW/sr/cm2/μm = 10-4 W/sr/m2/m.