This Demonstration calculates radiative heat transfer from the green surface to the black surface as a function of the temperature of the green surface. Both surfaces are blackbodies which lose energy by emission, but absorb all incident radiation. The blackbodies are maintained at constant temperatures by internal heaters. You can select "parallel plates", "perpendicular walls" or "parallel cylinders". The view factor is shown. The rate that heat transfers from the green surface and is intercepted by the black surface is plotted as a function of the temperature of the green surface. The magenta point on the plot represents the green surface temperature (select with a slider). You can change distances between surfaces and dimensions of the plates, walls or cylinders.