Throughout the past few years light simulation has been a fast growing method to accelerate the development process of components for the lighting industry. Most companies that have used light simulation in the development process are working not only with one, but with several different light simulation products. Independent of the simulation software used, the fundamental questions are virtually the same: how to realistically model the world? International Light Simulation Symposium (ILISIS) has the intention to bring together the light simulation software developers and their users. It is an opportunity for a scientific exchange about experiences in modelling optical behavior.