Radiance
Radiance is a physical quantity used in the sphere of radiometry to measure the intensity of a light beam, defined as power per unit solid angle per unit projected area.
| Φ | : | radiant flux [W] |
| θ | : | angle formed by surface normal and direction of radiance L [rad] |
| A | : | area |
| : | solid angle [sr] |
whereas
| Q | : | energy of light [J] |
| t | : | time [s] |
| : | energy of light at wavelength λ [J] | |
| λ | : | wavelength [m] |
| : | number of photons at wavelength λ | |
| : | energy of a photon at wavelength λ [J] | |
| h | : | Planck's constant |
| c | : | speed of light |