What is the Planck’s law?

As mentioned in FAQ section, the quantity of energy emitted by a true blackbody only depends on its temperature. This radiation level, named Radiant Emittance R, is defined by the following distribution discovered in 1900 by the German scientist, Max Planck:



  • h is the Planck’s constant,                      h=6.626 x 1034 Js
  • K is the Boltzmann’s constant,                 K=1.381 x 10-23 J/K
  • c is the speed of light,                           c=2.998 x 108 m/s
  • λ is the wavelength (in meters) 
  • T is the temperature of the blackbody in Kelvin: T (Kelvin) = 273,16 + t (Celsius degree).

Download our calculation sheet to determine the energy emitted by a true blackbody at selected wavelengths, depending on the temperature of the blackbody.