The theory of electromagnetic fluctuations as developed by Rytov was used to calculate the radiant power as a function of frequency radiated from a homogeneous isothermal sphere. The formula obtained is valid for all radii, frequencies, and complex dielectric constants. It is also shown that the emission coefficient computed from this theory is precisely equal to the absorption coefficient computed from the Mie theory. The formula obtained is readily adaptable to numerical calculations, and results are presented for the case of a good conducting sphere with a wide range of size parameters.
G. W. Kattawar and M. Eisner, "Radiation from a Homogeneous Isothermal Sphere," Appl. Opt. 9, 2685-2690 (1970)