When electron jumps from higher orbit to lower orbit, then energy is radiated in the form of electromagnetic radiation and these radiations are used to record the emission spectrum
Energy of electron may be calculated as $\mathrm{E}=-\frac{2{\mathrm{p}}^2{\mathrm{m}}_{\mathrm{e}}{\mathrm{Z}}^2{\mathrm{e}}^4}{{\mathrm{n}}^2{\mathrm{h}}^2}$
where, m_e = rest mass of electron $\mathrm{DE}=\left({\mathrm{E}}_{{\mathrm{n}}_2}-{\mathrm{E}}_{{\mathrm{n}}_1}\right)=13.6\times {\mathrm{Z}}^2\times \left[\frac{1}{{\mathrm{n}}_1^2}-\frac{1}{{\mathrm{n}}_2^2}\right]\mathrm{eV}$ per atom
This equation was also used by Rydberg to calculate the wave number of a particular line in the spectrum.
$\overline{\mathrm{v}}=\frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}{\mathrm{Z}}^2\left[\frac{\mathrm{I}}{{\mathrm{n}}_{\mathrm{I}}^2}-\frac{\mathrm{I}}{{\mathrm{n}}_2^2}\right]{\mathrm{m}}^{-1}$
where, RH = 1.1 × 10⁷ m^–1 (Rydberg constant)
For Lyman, Balmer, Paschen, Brackett and Pfund series the value of n₁ = 1,2,3,4,5 respectively and n₂ = ∞  for series limit, If an electron jumps from higher orbit n to ground state than number of spectral line will be nC₂. Ritz modified the Rydberg equation by replacing the rest mass of electron with reduced mass (µ) .
$\frac{1}{\mathrm{\mu }}=\frac{\mathrm{I}}{{\mathrm{m}}_{\mathrm{N}}}+\frac{\mathrm{I}}{{\mathrm{m}}_{\mathrm{e}}}$ ; Here, m_N = mass of nucleus, m_e = mass of electron.