In telecommunication, radiometry is the science of radiation measurement.
| 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 solid 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 |
Source: from Federal Standard 1037C
