I am certainly no expert, but I can explain how I usually set up the lighting for a scene. The first thing is, I always have some amount of ambient light in the scene just so polys aren't so dark when they aren't pointed directly toward a point-source (althought I doubt it is a requirement to have an ambient light source). Then for the point-sources, I play around with their "brightness" (have you tried something brighter than 20, 20, 20?). The problem might have something to do with the distance of the light source, its brightness, and the color of the objects in the scene.