What is shown in the simulation is [img]http://upload.wikimedia.org/math/1/0/c/10c96a8f2af7d9631a0f4dde5b817b62.png[/img].
It is the emitted power per unit area of emitting surface, [b]per unit solid angle[/b], and per unit wavelength (in unit of :angstrom). If integral over all solid angle, it need to be multipled by 4*?.