The  frequency  of radiation  absorbed  or emitted when transition occurs  between two stationary states with energies  E₁ (lower)  and  E₂ (higher)  is given by

According to Bohr's postulates:

The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by ΔE, is given by:

ν=$\frac{∆\mathrm{E}}{\mathrm{h}} =\frac{{\mathrm{E}}_2-{\mathrm{E}}_1}{\mathrm{h}}$​​

Where E_1​ and E₂​ are the energies of the lower and higher allowed energy states, respectively.