Imagine I have a 10x10x10cm cube filled with a scintillating material (material capable of generating light when energized). Three cameras are looking at this cube from three orthogonal directions (x, y, and z). Light is generated inside the cube and is refracted as it leaves the cube and reaches the camera. Although the cube wall is transparent, some light is reflected internally, and some light will not leave the cube because of total internal reflection. My goal is to reconstruct the distribution of light generated inside this cube in three dimensions. I have created a projection matrix, by ray tracing each pixel inside this cube back to the camera. However, I'm not sure how to approach the reflection problem as light may be bouncing around multiple times inside the cube. I have looked at Fresnel equation for reflection and the best I can think of is to trace each pixel to all pixels on the interior wall of the cube. Because the angle of incident is known, the fraction of light that is reflected from that particular ray can be calculated. The reflected ray can further be traced to the next wall and the fraction of light transmitted/reflected can be calculated. The problem with this approach is that it is computationally expensive and will result in a massive projection matrix. I am wondering if there is a more elegant way to approach this problem. Any help is greatly appreciated.