Abstract: We present an efficient method to simulate the propagation of wavefronts and approximate the behavior of light in an environment of freeform surfaces. The proposed method can emulate the behavior of a wavefront emanating from a point or spherical light source, and possibly refracted and/or reflected from a freeform surface. Moreover, it allows one to consider and to render images with extreme illumination conditions such as caustics. The proposed method can be embedded into rendering schemes that are based on scan conversion. Using a direct freeform surface Z buffer renderer, we also demonstrate the use of the wavefront approximation in illumination computation.