STEFANBOLTZMANN LAW

statement that the total radiant-heat energy emitted from a surface is proportional to the fourth power of its absolute temperature. Formulated in 1879 by Josef Stefan, an Austrian physicist, as a result of his experimental studies, the same law was derived in 1889 by Ludwig Boltzmann, also an Austrian physicist, from thermodynamical considerations: if E is the radiant heat energy emitted from a unit area in one second and T is the absolute temperature (in degrees Kelvin), then E = sT4, the Greek letter sigma (s) representing the constant of proportionality, called the StefanBoltzmann constant. This constant has the value 1.36 10-4 kilocalories per metre2-second-K4. The law applies only to blackbodies, theoretical surfaces that absorb all incident heat radiation.