Blackbody Radiation Think of the heat that a person feels from the embers of a fire. The energy that the body absorbs is radiated from the glowing coals. An idealization of this system that is more amenable to theoretical study is a red-hot block of metal a interior that can be observed through a hole small enough that the conditions inside the block are not perturbed. An ideal blackbody is shown in Figure 1. Under the condition of equilibrium between the radiation field inside the cavity and the glowing piece of matter, classical electromagnetic theory can predict what frequencies v of light are radi ated and their relative magnitudes.