After all rays have been fired for a particular irradiance evaluation, this feature looks at the resulting ray color of each hemisphere cell and then sends additional rays through those cells that greatly differ from their neighbors. This returns a more detailed look at high contrast areas of the environment and so a more accurate estimate. Currently about 25% more rays are fired, so for a setting of 100 rays you really get 125, but the results are better than if you just use a setting of 125 without supersampling, because the rays will be going in the more important directions.