Abstract: Precise quality control for hierarchical lighting simulations is still a hard problem, due in part to the difficulty of analysing the source of error and to the close interactions between different components of the algorithm. In this paper we attempt to address this issue by examining two of the most central components of these algorithms: visibility computation and the mesh. We first present an investigation tool in the form of a new hierarchical algorithm: this algorithmic extension encapsulates exact visibility information with respect to the light source in the form of the backprojection data structure, and allows the use of discontinuity meshes in the solution hierarchy. This tool permits us to study separately the effects of visibility and meshing error on image quality, computational expense as well as solution convergence. Initial experimental results are presented by comparing standard quadtree-based hierarchical radiosity with point-sampling visibility to the approaches incorporating backprojections, discontinuity meshes or both.