In the 3D world, caustics and global illumination are one of the easiest ways to create realistic lighting. Although memory-hungry, these effects — also called photon effects — are well worth the time.
Very quick and physically accurate global-illumination and caustic lighting can be simulated. To do this, energy is emitted into the scene in the form of simulated photons. The final density of these photons on diffuse surfaces in the scene is computed and stored in the photon map.
