The look and some effects of the expensive Final Gather technique can be simulated with this light shader. PhysicalSkylight uses an HDRI environment map to light the scene and renders fast ambient occlusion shadows from the direction of the light source.
To accurately simulate a final gather look it is necessary to pre-filter the environment map in an external program using a technique called spherical harmonics.
Unlike true final gather, this technique does not introduce unwanted flicker in animation sequences, but it also does not handle secondary bounces.
Usage
This light shader is best suited for outdoor environments such as overcast daylight on a cloudy day. It is not intended for interior renders but may be used for directional ambient occlusion.
PhysicalSkylight can also be used to bring out small details in a scene without creating the dirty look of a multiplied occlusion pass.
