On the radiation from small particles

The laws of equilibrium radiation within cavities and from surfaces of bodies must be recast when the cavity or body dimension is of the same order as the wavelength being considered. New formulae for the Planck function, the Wien displacement law, and the Stefan-Boltzmann law for small spherical particles are presented in this paper in terms of the three independent variables temperature, wavelength, and diameter. The most significant element of the formulation for black particles is that radiant emission, or absorption, is not permitted at wavelengths greater than √2π times the particle diameter.