Specifies the number of samples the Progressive Lightmapper uses for direct environment lighting calculations. The default value is 256. The range is 8 to 131072.
Note that for indirect lighting only 1 environment sample per bounce per indirect sample is used. Noise introduced by the environment in indirect lighting can be reduced by increasing the indirect sample count. If you increase this value, the quality of your lightmaps might improve, but baking takes more time.