Caustics are created when light which has been specularly reflected or refracted is focused and dispersed indirectly iluminating a diffuse surface. Extra information must be specified in the lighting property editor for indirect illumination of caustics effects to occur in the scene.

Lights in the scene must be defined as photon emitters and therefore energy values as well as colors can be adjusted. Light energy is differnet in concept from the light color, it has a physically based energy contribution to the scene and will be conserved. Therefore all light emitted from the light source will appear as illumination in the final rendered image.

Point, spot and area lights are emitted in diverging directions and as in reality the light energy falls off using the inverse square of the distance. This is unlike usual light shader color which generally falls off in a linear fashion. As this is the case high levels of energy ranging into the thousands must be specified to illuminate distant objects whilst light shader color parameters can range from 0 -1.

The positon and parameters of the of the light are paramount in the creation of caustic effects. It is important that emitted photons hit objects which can store them. A point light in the scene that has only one small hidden photon absorber can cause most photons to be lost and error messages will occur in the rendering process.

With glass material fractions that are reflected and transmitted depend on the angle of incidence. When a beam strikes a glass surface at a glancing angle it is mainly reflected when it is perpendicular o the surface most of it passes through.With a transparent material such as glass there will be both reflection and refraction of light depending on the relative angle and position of both glazing and light. It is easier to view the effects if the light's color and intensity are turned off and the scene ambience set to black. The picture to the right was rendered with only the caustics on and the scene ambience set to black.