This paper addresses the integration of the daylight effect during the early stages of the architectural design process. The first part presents a design assistance method that helps designers to characterize their daylight intentions and materialize them in architectural solutions. In this part, we describe the implementation of this method in a design tool, denoted DaylightGen, the implemented process and the different system components. The second part of this paper focuses on the investigation of the potential of the proposed method in design process. It was evaluated in educational design case study. This part integrates the experimentation process and his results.