Preparing Object Surfaces
 
 
 

To achieve a good caustic or global illumination effect, you have to set up your geometric objects' shaders in such a way as to enhance the effect. Here is a short checklist of things to keep in mind:

Both scenes (below) have the same setup, same shaders, and an equal number of lights. Notice in the second scene how the side of the desk with drawers is illuminated with ambient light, whereas the image above it has a very sharp falloff that appears less realistic when compared to a render using global illumination.

This scene has not been rendered with global illumination.

This scene uses a high Photon Reflection setting that causes the light from the windows to hit the floor and bounce off the walls.