Wien's law is concerned with

1. relation between emissivity and absorptivity of a radiating surface
2. total radiation, emitted by a hot surface
3. an expression for spectral distribution of energy of a radiation from any source
4. a relation between the temperature of a black body and the wavelength at which there is maximum radiant energy per unit wavelength

According to Wein's displacement law, product of wavelength belonging to maximum intensity and temperature is constant i.e., λ_mT = constant.