where c is the speed of light or (2.9979)10 m/s, k is Boltzmann's constant or (1.38)10 J/K, h is Planck's constant or (6.626)10 J s, v is frequency (s), and the quantities K v and L v are the energy and entropy fluxes per unit frequency, area, and solid angle. In deriving this blackbody spectral entropy radiance, with the goal of deriving the blackbody energy formula, Planck postulated that the energy of a photon was quantized (partly to simplify the mathematics), thereby starting quantum theory.