Advanced computer simulation tools for analyzing daylighting features and thermal performance of buildings are improved at the Fraunhofer Institute for Solar Energy Systems.For an analysis of daylighting elements in lighting simulations, new light-deflecting structures and materials have been measured and modeled. In order to study the interaction between lighting and thermal behaviour of rooms, thermal and lighting simulation techniques are linked together. Thus, integrated energy concepts can be evaluated. Programs for handling parallel image generation in a network of high-performance Unix workstations have been developed.