What I did this week was to do correct photon absorption and power adjustment. This is done through a randomized method called Russian Roulette. Here's a quick summary: when a photon hits a surface, given the surface is not a 100% reflective (mirror), the photon will bounce off with less power. Instead of casting a photon with decreased power, Russian Roulette method casts the photon with a probability equivalent to the reflectivity of the surface. When integrating (averaging) photon powers to get the reflected radiance, the results are the same. This is an optimization since less photons will have to be cast total, and thus less would have to be integrated.