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Expressions for the transmissivity of an interface between two dielectrics, averaged over all directions of incidence and over all polarization directions, are given, and the results are tabulated and graphed. When the radiation is incident from the medium with lower index of refraction, the average transmissivity Tav(n) differs from the transmissivity at normal incidence by less than 6% for values of the ratio of the indices of refraction, n, between 1 and 8. The average transmissivity when the light is incident from the high-index side of the interface is smaller than Tav(n) by a factor n−2. The connection of the results with the blackbody flux in a dielectric is noted. The results are used to estimate the energy density in a dielectric when isotropic radiation is generated internally.
Frank Stern (Wed,) studied this question.