Hi, the importance sampling have a limit parameter. Its default setting is 1. The help manual says The limit parameter is used to define the maximum solid angle in Steradians of the target sphere as seen from the scatter point. So I assume its maximum value cannot exceed 4*pi? But it turns out I can use any values I want to set the limit parameter. 

Could you tell me if I understand the manual correctly?

Thanks so much 

Erkang