Since CAD models can be used for other requirements than light simulation, the geometry model frequently causes problems in the simulation. While the wire cables of a banister can easily be designed as high-resolution cylinders in a CAD program, the calculation of the cylinder surface is complicated to render. The designer must take this into account as early as possible in the preparation of the 3D model in order to review the export settings. Since simulations require extensive calculations and will continue to do so, an optimised geometry considerably reduces the work and time involved in producing light simulations. Small, highly detailed geometries on a separate, inactive layer can reduce the calculation time. Similarly, it is advisable to use a material-based layer structure for quick provisional calculations.