Specifies the number of samples the Progressive Lightmapper uses for indirect lighting calculations. (Editor only).
The range is 8 through 131072. The default value is 512. If you increase this value, the quality of your lightmaps might improve, but baking takes more time.
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 Indirect Samples property in the Lighting Settings Asset Inspector.
Additional resources: Lighting Settings Asset.