The science of radiation measurement. See Table of Radiometric Terms. TABLE OF RADIOMETRIC TERMS Term Symbol Quantity Unit radiant energy Q energy joule (J) radiant power Synonym optical power power watt (W) irradiance E power incident per unit area (irrespective of angle) W•m-2 spectral irradiance E irradiance per unit wavelength interval at a given wavelength W•m-2•nm-1 radiant emittance Synonym radiant exitance W power emitted (into a full sphere) per unit area W•m-2 radiant intensity I power per unit solid angle W•sr-1 radiance L power per unit angle per unit projected area W•sr-1•m-2 spectral radiance L radiance per unit wavelength interval at a given wavelength W•sr-1•m-2•nm-1