Stefan’s law states that the total amount of heat energy radiated per second per unit area of a perfect black body is directly proportional to the fourth power of its absolute temperature.
E α T4 or E = σ T4
where σ is called Stefan’s constant.
Its value is 5.67 x 10-8 W m-2 K-4
It is also called Stefan – Boltzmann law, as Boltzmann gave a theoretical proof of the result given by Stefan.