It states that an electron might make a transition from one of its
specified non-radiating orbits to another of lower energy When it
does so, a photon is emitted having energy equal to the energy
difference between the initial and final states The frequency of the
emitted photon is then given by
hn  =   Ei – Ef
(12 6)
where Ei and Ef are the energies of the initial and final states and Ei > Ef