For conditions of thermodynamic equilibrium, together the number densities n _ 2 and n _ 1, the Einstein coefficients, and the spectral energy density provide sufficient information to determine the absorption and emission rates.
12.
Along with detailed balancing, at temperature we may use our knowledge of the equilibrium energy distribution of the atoms, as stated in the Maxwell Boltzmann distribution, and the equilibrium distribution of the photons, as stated in Planck's law of black body radiation to derive universal relationships between the Einstein coefficients.
