Radiosity

Radiosity is similar to ray tracing in that it maps out the light sources in a 3D scene and calculates the paths that they take from the viewer back to the source. During their path, they interact with different objects and will reflect off of objects. Radiosity is even better than ray tracing because it is a more complete model. Not only does the radiosity model map out the paths of the light sources to the viewer and the interaction with objects, it also takes into account the interreflections that occur between diffuse object surfaces. This type of lighting is called second, or indirect, lighting. This image is from Radiance, a UNIX freeware copyrighted by the Regents of the University of California (Go Bears).

Pretty hallway

If you remember, diffuse lighting is light factor for an object, where the source direction is clear, but the object will remain lit from that side no matter where the viewer is. Well, in scenes where we have light coming from a source and bouncing off of objects, this is a factor that comes into play, because objects themselves will cast off light. Objects that have diffuse surfaces affect the illumination of the whole scene because light comes from objects in the scene as well as from the light sources. Radiosity is calculated by breaking down the original surfaces into even smaller pieces, which are called elements. Then, the amount of illumination that occurs between elements is stored. Realize that EACH element's interaction with every other element is stored! This is why radiosity takes so long to calculate, and can certainly not be done in realtime. Radiosity does not handle specular reflections.

Nicely lit room

       

Good reading light!