The spectral intensity of a blackbody, I λ λ , b was first determined by Max Planck. It is given by Planck's law per unit wavelength as: I λ λ , b ( λ λ , T ) = 2 h c 2 λ λ 5 ⋅ ⋅ 1 e h c / k B T λ λ − − 1 This formula mathematically follows from calculation of spectral distribution of energy in quantized electromagnetic field which is in complete thermal equilibrium with the radiating object. Planck's law shows that radiative energy increases with temperature, and explains why the peak of an emission spectrum shifts to shorter wavelengths at higher temperatures. It can also be found that energy emitted at shorter wavelengths increases more rapidly with temperature relative to longer wavelengths.