Getting things evenly spaced is known mathematically as a "packing problem". I know there are formulas for covering an entire sphere with evenly placed centers for much smaller spheres, which would eliminate your convergence problem and the resultant need to modify each and every light source's strength. That particular reference was in a ScienceNews article a couple years back, so I don't have it at my fingertips. A web search on "packing problem" ought to turn up this example though. Carolly