Focus on light
The term "caustics" is used to describe phenomena such as the flare of light on the table from light shining through a bottle or glass. The formation of the hot-spot itself can be thought of in terms of raytracing, which explains why you don't see them in Phong or radiosity renderings. On the other hand, you only see it because the light, once focused, is diffusely reflected off the table to your eye. This is pretty advanced rendering. As shown in the image at right, the "VRAY" rendering includes the ability to render caustics.
Last updated: April, 2014