This idea was first prototyped in the Moria environment for LOTR. Based on Debevec’;s Radiance idea for image based lighting, A line of pre-rendered spherical views was strung out along the path of the Cave Troll and the ambient / bounce light was provided by interpolating between the spheres based on the Troll’s position.
Radiance Maps are a quick and dirty way to simulate diffuse inter-reflection of the environment onto active objects in a game engine. They are similar to environment or reflection maps, but are intended to create low frequency reflections. They can therefore be much lower resolution. The maps used in this demo are 16 by 16 pixels, and could be even lower as they were blurred with a 4×4 box filter before application.
As you can see, when the active object passes into shadow we can see the bounce light from the sky having an effect on the ambient shade, and when in full sunlight, the strong bounce light from the ground showing up on the underside.
As a comparison, the left most image is a normal Key Light + Ambient light setup, the middle one is a Radiance Sphere + Key Light setup and the rightmost is a full Reflection only to demonstrate what’s actually happening at the unfiltered reflection level.