Radiosity

Ideally the ambient light at some point on an object is the integral over all surfaces in its surroundings of the light emitted in its direction.

This may be approximated by summing the light reflected in its direction by each of the polygonal facets in the surroundings.

The complication is that each of these contributions contains a term from the facet being considered, so that the result is a set of simultaneous equations

Various approximations to the solution of this problem have been proposed.

Ray Tracing

This is used in place of simple z-buffer or scanline hidden surface elimination, and surface normal shading.

It traces the route backwards of rays from a scene striking in turn each pixel of the screen in a virtual camera.

Each ray is traced back to see which surfaces it would strike. The surface that is hit nearest to the camera (the 'first hit') is used to control the colour of that pixel.

Features:

Advantages over simple hidden surface removal with ambient shading are:

A number of raytracers are available.
A good test is the Stanford Bunny (69,451 polygons)