Caustics refers to the bending and refraction of light when passing through transparent materials.

Caustics can be set for a transparent object to change the way the object treats light passing through it.

Caustic Refraction

Example of caustic refraction for some transparent objects.

A caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface.

The Caustic effect produces focused light and shadow effects from a point light.

This is a glass bowl of apples, (with a pyramid procedural bump effect), and a glass cone, rendered with transparency and refraction, and with Caustic effects. (Reflection 0.90, refraction 1.15).

These scene is illuminated with a spotlight.

See also: Caustics