The interesting parts of this image are the smooth edges for the lights. If you look closely at the right edge of the light on the floor from the cone lamp on the left, you'll see concentric (or almost concentric) rings of various shades. This is because there are really 5 light sources in the cone lamp. In fact, all the other light sources are also actually 5 lights. It's not perfect, but it makes for a more photo-realistic image (although utilizing radiosity in addition to ray tracing would have worked too).