There is a simple and interesting relationship between the peak wavelength and the temperature at which a blackbody radiates. Wilhelm Carl Werner Otto Fritz Wien (1864–1928), a Nobel prize recipient in 1911, discovered this behavior of the blackbody [Eq. (1.12)]. The equation states that the product of the peak wavelength and the source temperature is constant, which means the peak of the radiation shifts to shorter wavelengths as the temperature increases. Figure below shows the displacement of the peak wavelength.

Applying Planck's law, the spectral radiant emittance at the peak wavelength is

*Wien's displacement law.*