In
radiometry,
photometry and
color science, a
spectral power distribution (
SPD) measurement describes the
power per unit
area per unit
wavelength of an
illumination (
radiant exitance). More generally, the term
spectral power distribution can refer to the concentration, as a function of wavelength, of any radiometric or photometric quantity (e.g.
radiant energy,
radiant flux,
radiant intensity,
radiance,
irradiance,
radiant exitance,
radiosity,
luminance,
luminous flux,
luminous intensity,
illuminance,
luminous emittance).