Radiation energy per unit time is given Stefan-Boltzmann law as being proportional to temperature to the 4th power, and to surface area of the body. (For black bodies) This was told to me in our physics lecture. Later for a non black body it is the same except being multiplied by another constant called the emissivity of the body I am told emissivity is the ratio of the radiant energy emitted by a black body in unit time to the energy emitted by the body in hand. This makes perfect sense till the time I am told that:
Emissivity of the body depends on temperature of the body. This can only give 2 conclusions: Either radiant energy emitted per unit time is not proportional to temperature to the 4th power or, Regular bodies do not emit energy like blackbodies. If this is true, is there an alternate more accurate radiation heat transfer models for regular bodies, what are they? Also tell me which conclusion is correct?