Hello, I consider a Lambertian spherical emitter with radius R and placed at the point (0,0,h). I would like to compute the irradiance received by the infinitesimal surface patch at (0,0,0) whose normal is the vector (0,0,1). - My question is: is it possible to convert this calculation into calculating the irradiance received from an "equivalent" disk-shaped emitter placed at (0,0,h) ? - Is it correct to compute the flux received by each patch of the disk and then using it to compute the irradiance at (0,0,0)? (I know all this this might sound useless, but I am trying to re-cast the original problem because I will later need to compute the irradiance received from portions of the sphere, and it is easier to handle portions of a two dimensional disk instead). Thanks.