For lighting simulations in architecture there is the need for correct illumination calculation of virtual scenes. The Radiance Synthetic Imaging System delivers an excellent solution to that problem. Unfortunately, simulating complex scenes leads to long computation times even for one frame. This paper proposes a parallelization strategy which is suited for scenes with medium to high complexity to decrease calculation time. For a set of scenes the obtained speedup indicates the good performance of the chosen load balancing method. The use of MPI delivers a platform independent solution for clusters of workstations (CoWs) as well as for shared-memory multiprocessors (SMPs).