 The result is much the same as with reflective colour, but because of the process of absorption and emission, the substance emits a glow.According to Planck, the energy of each photon is given by multiplying its frequency in cycles per second by a constant (Planck's constant, 6.626 x 10−27 erg seconds).It follows that the wavelength of a photon emitted from a luminescent system is directly related to the difference between the energy of the two atomic levels involved.