Glossary

Diffusion: phenomenon by which a radiation is deflected in various directions by interaction with other objects
Reflectance: reflection coefficient related to the intensity
Divergence: defines the maximum angle between the light rays of a beam
Irradiance ( radiometry ): optical power received by unit area
Radiance ( radiometry ): for a light source or a diffusing/reflecting surface, power emitted per unit of solid angle and per unit of apparent area