Efficient Radiosity for Daylight Simulation in Closed Environments


Radiosity is a useful tool for architects and lighting engineers to simulate illumination in the interior of buildings. Unfortunately, the computation time for radiosity is very high. However, radiosity algorithms can take advantage of special scene properties of specific classes of environments. Exploiting the additional information about the scene structure of a particular class can decrease the computation time significantly. The aim of this paper is to speed up the radiosity computation for the class of closed environments without artificial light sources.

Two Restrictions on the Scene Structure

The first restriction on the scene is that it is closed. The reason for this restriction is the fact that radiosity is based upon the energy conservation principle, that means that at any time the amount of emitted energy equals the amount of absorbed energy plus the amount of energy leaving the scene. In closed scenes no energy leaves the scene, thus simplifying the radiosity computation. However, this restriction does not impose problems, because radiosity is mostly used for interior scenes. The second restriction is that only daylight can be considered. Radiosity algorithms solve a set of equations, where the radiosities of patches are the unknowns and the emissions are the constant terms. In conventional radiosity all patches are allowed to emit light, i.e. to be an artificial light source. If we assume that no patch has emission, we only have to consider daylight. This allows the use of very efficient solution methods known in numerical mathematics for the set of equations. The second restriction does not limit the range of applications too much as well, because in most cases architects are interested in visualizing their design with daylight conditions.

Mathematical Foundation of the New Method

Details will be described in the final paper.


The new method reduces the computation time of both the radiosity evaluation and of image generation. Images can be generated at interactive rates even for very complex scenes, making the method suitable for walk-throughs and VR-applications. Since numerical techniques are mainly replaced by analytical formulas, no aliasing effects appear.

Conclusion and Future Work

The development of radiosity algorithms for special classes of scenes is a promising field of future research. Such algorithms are significantly faster and possibly more accurate than non-specialized algorithms.

Last update: March 23, 1995. If you have any comments, please send a mail to wp#cg.tuwien.ac.at.

Werner Purgathofer, Institute of Computer Graphics, Technical University of Vienna.