Specifies the radius the Progressive Lightmapper uses to filter the indirect lighting component of the lightmap when you use the Gaussian filter. (Editor only).
The range is 0.0 through 5.0. The default value is 5.0. A higher value increases the strength of the blur, which reduces the amount of noise from indirect light in the lightmap.
This setting affects lightmaps generated by the Baked Global Illumination system. It only applies to the the Progressive Lightmapper.
When Unity serializes this LightingSettings object as a Lighting Settings Asset, this property corresponds to the Filtering > Indirect Filter > Radius property in the Lighting Settings Asset Inspector.
Additional resources: Lighting Settings Asset.