| Table 1. Energy photometric quantities1 | |
|---|---|
| Quantity | Unit |
| 1Common synonyms and explanations are given in parentheses | |
| Radiation energy (radiant energy) ............... | J |
| Radiation flux (radiant flux) ............... | W |
| Luminous intensity (radiant intensity) ............... | W × sr–1 |
| Radiance ............... | W × sr–1 × m–2 |
| Irradiance (illuminance) ............... | W × m–2 |
| Energy luminosity ............... | W × m–2 |
| Energy exposure ............... | J × m–2 |
| Radiant intensity effect (the time integral of luminous intensity over the duration of a radiation pulse) ............... | J × sr–1 |
| Spectral density of energy photometric quantities (the derivative of the quantity with respect to the wavelength or some other spectral coordinate) ............... | |
In studies of the physical effects of the interaction between radiation and matter (photoelectric, photochemical, luminescence, and other effects), the energy photometric quantities are sometimes expressed in units of the photonic system. In this system, radiation energy is given by a dimensionless quantity, the photon number; radiation flux is given by the “flow” of photons per second (sec–1); and the dimensions of the unit of luminous energy intensity in this system are sec–1 × steradian–1 (sr–1).