Lighting Design Glossary

Participating Medium

(Term of optics/computer graphics)

Material of a property that affects the transport of light through its volume. Examples include glass, water, fog and smoke. Clear air is also a participating medium, but one that only has a measurable effect over great distances.

A participating medium influences the travel of light by its extinction coefficient, which determines the amount of light that doesn't travel straight through per amount of distance, and is the sum of the scattering coefficient and the absorption coefficient. The ratio between the scattering coefficient and the absorption coefficient is called scattering albedo.

In the Radiance software, participating media are modelled by means of the mist material type.