Lighting simulation is becoming increasingly more important as a method for design and evaluation. There is a wide range of packages that provide the accuracy and the usability in lighting simulation. Relux developed by Relux Informatik AG, Switzerland, Relux offers users innovative and high-performance light planning software with open interfaces and simultaneous access to the latest product data from luminaire and lamp manufacturers. The goals of this report is to explore some of the lighting simulation issues relating to Relux. It is hoped that it will provide some background information that will enable a designer and engineer to make some informed judgements on the potential of the current state-of-the-art in computer prediction of lighting in buildings and how this may be used to assist in building design.