In this paper, we use the validation test cases initialized within the subtask C, "Daylight design tools", of IEA SHC Task 21, "Daylight in buildings" to assess the accuracy of a commercial lighting software, Lightscape 3.2. We first analyzed the applicability and the limitations of the IEA 21 test cases, and we concluded some directives for validation test cases in order to guaranty its applicability to assess any lighting software.