“…Although there is a huge literature on the radiosity equation in computer graphics, see the references in [7, 20 25], there are not so many mathematical investigations on the structure, for example regularity, of the solution ū of (1.1). Existence theory in the L p (S) spaces, p ∈ [1, ∞], or in spaces of continuous functions, under certain assumptions on S and E, can be found in [1,3,4,10,16,17]. In [17] the properties of ū along an edge were studied, if the function E is differentiable and in [3] one finds results for the regularity of ū near corners in the two-dimensional cases.…”