My understanding of ray tracing is that it maps out luminance for a scene. Now with ray tracing (backwards ray tracing that starts from the camera outwards) does each ray have a luminance value associated with it? In the case of a perfectly diffuse surface, can one simply take the mean of all of the secondary rays luminance to arrive at a luminance value for the primary ray or is this assumption wrong? If L0 are the primary rays luminance, and L1 ,L2 ,L3, L4 ,L5 are the secondary rays that are created due to the diffuse surface. (see Diagram for explanation).