A convenient way to model radiation between a surface and a point is to use surface-effect elements superimposed on surfaces that emit or receive radiation. The following such elements are available: SURF151 for 2D models and SURF152 for 3D models. The element option KEYOPT(9) activates radiation for these elements. The view factor can be specified as a real constant (defaults to 1) using KEYOPT(9) = 1, or you can calculate a cosine effect (using KEYOPT(9) = 2 or 3) from the basic element orientation and the extra node location.