Notes. The elapsed time for the photon shooting phase of a simulation is divided by the number of grid cells crossed during that phase. The result is an indication of the time spent per cell crossing, including grid traversal calculations and some overhead for generating the random paths and for storing results. The tests were performed on a typical desktop computer using a single core. The last column lists the ratio between the run times for the Voronoi and octree grids. Larger numbers indicate slower performance.