Using the implicit equation x = 4 ( 1 − − e − − x ) yields the peak in the spectral radiance density function expressed in the parameter radiance per proportional bandwidth. (That is, the density of irradiance per frequency bandwidth proportional to the frequency itself, which can be calculated by considering infinitesimal intervals of ln ⁡ ⁡ ν ν (or equivalently ln ⁡ ⁡ λ λ ) rather of frequency itself.) This is perhaps a more intuitive way of presenting "wavelength of peak emission". That yields x = 3.920 690 394 872 886 343....