The light simulation has proven to be a useful tool in the visualisation and verification of the lighting design. Initially, a number of steps are required for the preliminary planning of the rendering: the concept idea and the sketch, the 3D CAD model and the specification of the light sources and surface properties. For professional light simulations, the designer uses specialised software such as 3ds VIZ/Max or DIALux. Most CAD programs are not able to simulate light with physically accuracy.