Specifies the filter kernel that the Progressive Lightmapper uses for the direct lighting. (Editor only).
When this is set to None, the Progressive Lightmapper does not filter direct lighting. When this is set to any other value, the Progressive Lightmapper filters direct lighting with the specified filter.
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 > Direct property in the Lighting Settings Asset Inspector.
Additional resources: Lighting Settings Asset.