Create a photon map light source. The tool evaluates the illumination in the current scene and stores it to a photon map object. The scene must include ordinary light sources which cast photons around.

The tool has the following options: Settings - render settings to define how accurately photon bounces are traced. Recursion depth and threshold play an important role here. Rendering settings have a dedicated section in the misc tab for controlling photon mapping. For example, the desired photon count is defined there. Include Direct Photons - A special option to capture direct illuminaion from light sources. Usually this is not desirable as direct illumination is faster and more accurate to compute using ray tracing. When using this option, original lights should probably be erased; otherwise the photon map will duplicate their illumination. Note Usually photon mapping works best in closed interior scenes, where all traced photons contribute into the overall illumination. For other kind of scenes, use of spot lights is recommended; spot lights emit the photons efficiently along the defined light cone. This can speed up photon map rendering significantly. An example of a challenging photon map setup is a scene, where small objects are placed around a point light. In such a scene, 99.99% of photons can end up into empty space, creating nothing visible but just slowing down the rendering. See also: Models/Geometrics/Light Sources/photon map and Tutorials/Rendering/photon map Illumination.

Photon mapping applied to an architectural scene. Courtesy of Pixel Perfect.