For easy demonstration of the discontinuous release of energy by free electrons upon collision with neon atoms, and the discreet energy states in neon atoms, as well as for determining the first excitation energy level. The Franck-Hertz curve is plotted either point-by-point with indicating instruments or continuously by means of a recorder or CASSY.
The relaxation of the neon atoms occurs partly via transitions in the visible region. Therefore, light bands corresponding to the various states of excitation can also be observed.