Radiometry

In telecommunication, radiometry is the science of radiation measurement.

TABLE OF RADIOMETRIC TERMS
Term Symbol Quantity Unit

radiant energy Q energy joule (J)

radiant power Synonym optical power φ power watt (W)

irradiance E power incident per unit area (irrespective of angle) W·m^-2

spectral irradiance E_λ 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 solid angle per unit projected area W·sr^-1·m^-2

spectral radiance L_λ radiance per unit wavelength interval at a given wavelength W·sr^-1·m^-2·nm^-1

TABLE OF RADIOMETRIC TERMS
Term	Symbol	Quantity	Unit
radiant energy	Q	energy	joule (J)
radiant power Synonym optical power	φ	power	watt (W)
irradiance	E	power incident per unit area (irrespective of angle)	W·m^-2
spectral irradiance	E_λ	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 solid angle per unit projected area	W·sr^-1·m^-2
spectral radiance	L_λ	radiance per unit wavelength interval at a given wavelength	W·sr^-1·m^-2·nm^-1

Source: from Federal Standard 1037C