Planck's law for the spectrum of black-body radiation predicts the Wien displacement law and may be used to numerically evaluate the constant relating temperature and the peak parameter value for any particular parameterization. Commonly a wavelength parameterization is used and in that case the black body spectral radiance (power per emitting area per solid angle) is: u λ λ ( λ λ , T ) = 2 h c 2 λ λ 5 1 e h c / λ λ k T − − 1 .