For my master thesis for Civil Engineer in computer science at the Katholieke Universiteit Leuven (Belgium), I investigated the Lightcuts algorithm proposed by Walter et al. This algorithm allows calculating the illumination from many or complex light sources efficiently. In addition to implementing and evaluating their algorithm in PBRT, I also investigated two (small) extentions. The first improves the estimated error by also taking the visibility of the light sources into account and calculating a lower bound on the contribution of light sources (next to the upper bound used in the original paper). In the second extention the coherence between the cuts constructed for neighbouring pixels is exploited to reduce the cost of determining a good approximation. The full text and a short summary of it are available in Dutch but I also wrote a paper in English on the Coherent Lightcuts extention I proposed.
If anyone should be interested in the PBRT source code of my implementations (Lightcuts, Multidimensional Lightcuts, Lightcuts + Visibility bounds and Coherent Lightcuts), just send me a mail and I will gladly provide it.
UPDATE 10/12/2008:
After the first request for the source code I created a small page with a link to the package and some basic info
here.
Thomas De Bodt (thomas_de_bodt@hotmail.com) - Katholieke Universiteit Leuven - 2007-2008