In this simulated scene the light shining through the specular glass window is casting caustic effects onto the diffuse surfaces in the room. Objects which receive caustic effects must have be assigned a diffuse surface as photon shaders on these objects store energy information in the form of a photon map used in the rendering process. Objects in the scene must be assigned photon shaders to reflect, transmit or store photons.

Caustics are created when specular light is focused onto diffuse surfaces. Materials which transmit photons such as the glass window are mainly specular as diffuse surfaces spread the light rather than focusing it. The glass required a Phong, Blinn, or anisotropic surface shader as the caustic effects are created by it's specularity. The diffuse component of the material was turned off.

Photon shaders on objects with a diffuse or partially diffuse surface will store energy information in the form of a photon map which is used in the rendering process. The room surfaces which recieve the caustics were assigned a diffuse material with the specular highlight turned off in the material property editor.

Objects that cast, receive, or create caustics cannot be black so the object’s diffuse color cannot be of RGB value (0.000, 0.000, 0.000). This is because totally black objects absorb photons so caustic effects which are caused by reflection and trasnmittance will not be produced.

Material Shaders on objects compute the direct illumination as usual and add the indirect caustic illumination by collecting nearby photons from the photon map and adding their contribution.