In atomic physics, The Rydberg formula is used to describe the wavelengths of spectral lines of many chemical elements.
The modified Rydberg formula given below is used for any hydrogen-like chemical elements.
λvac= the wavelength of the light emitted in vacuum;
R = the Rydberg constant for this element;
Z = the atomic number, i.e. the number of protons in the atomic nucleus of this element;
n1and n2= integers such that n1< n2, corresponding to the principal quantum numbers of the orbitals occupied before and after.