Planck Radiation Law and Radiative Transfer

A.1 Planck Radiation Law Blackbody objects (i.e., perfect emitters of energy) whose temperatures are greater than absolute zero emit energy E per unit volume and per unit frequency at all wavelengths according to the Planck radiation law (A-1) where h = Planck's constant = 6.6256 x 10-34 J-s, kB = Boltzmann's constant = 1.380662 x 10-23 J/K, c = speed of light = 3 x 108 m/s, T = physical temperature of the emitting object in degrees K, f = frequency at which the energy is measured in Hz. Upon expanding the exponential term in the denominator, Eq. (A-1) may be rewritten as (A-2).