Table 13.

A brief summary of radiometric quantities as they apply to non-contact thermometry

Quantity	Quantity symbol	Typical description	SI unit
Power, radiant flux	ϕ	Collected by an optical radiation detector	W
Irradiance	E	Radiant flux per area at the detector	W m−2
Radiance	L	Radiant flux in a defined beam and a given direction per area at the source	W m−2 sr−1
Exitance	M	Radiant flux per source area emitted by a source into the hemisphere	W m−2
Radiance temperature	TR	Temperature derived from radiant flux with an emissivity of unity for the source	K