An equivalent way to view a SLF is as a function from the surface to lumispheres, where a lumisphere is a function from direction to color that represents the radiance leaving a point in all directions. This is the viewpoint that we take in our work. All of our techniques will make use of the fact that the lumisphere encodes a whole sphere of light and not just an outward facing hemisphere. We use lumispheres that are piecewise-linear with respect to a tesselation of the sphere which is described in the paper.