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Introduction to Radiosity.

The 'radiosity' method of computer image generation has its basis in
the field of thermal heat transfer.  Heat transfer theory describes
radiation as the transfer of energy from a surface when that surface
has been thermally excited.  This encompasses both surfaces which
are basic emitters of energy, as with light sources, and surfaces which
receive energy from other surfaces and thus have energy to transfer.

This 'thermal radiation' theory can be used to describe the transfer of
many kinds of energy between surfaces, including light energy.

As in thermal heat transfer, the basic radiosity method for computer
image generation assumes that surfaces are diffuse emitters and
reflectors of energy, emitting and reflecting energy uniformly over
their entire area.  It also assumes that an equilibrium solution can be
reached, such that all of the energy in an environment is accounted
for, through absorption and reflection.

The basic radiosity method is viewpoint independent. The distribution
of energy in the scene is the same regardless of the viewpoint of the
image.