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 | Φ | power | watt (W) |
| irradiance | E | power incident per unit area (irrespective of angle) | W•m-2 |
| spectral irradiance | Eλ | 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 | Lλ | radiance per unit wavelength interval at a given wavelength | W•sr-1•m-2•nm-1 |