For a black body, Planck's law gives:::formula_2whereformula_3 (the Intensity or Brightness) is the amount of energy emitted per unit surface area per unit time per unit solid angle and in the frequency range between formula_1 and formula_5; formula_6 is the temperature of the black body; formula_7 is Planck's constant; formula_1 is frequency; formula_9 is the speed of light; and formula_10 is Boltzmann's constant.