The spectral lines of hydrogen are produced when hydrogen gas is excited using a high-voltage source. This means that the electrons in the atom are actually excited, and thus emit radiation. Importantly, the visible spectrum of the hydrogen atom, called the Balmer series of spectral lines, corresponds to a series of bands, meaning that only certain wavelength of light are actually being emitted by the atoms. This fitted with what Planck said about the energy being radiation being quantised.

Balmer was able to derive an empirical equation for the wavelengths of the spectral lines of hydrogen, which was later modified by Rydberg:

<<Insert eqn here>>

Where RH is the Rydberg constant, given on the data sheet

And ni and nf are integers.

Balmer of course did not know what these integers represented, they simply fitted the data well.

Bohr’s challenge was to then try to explain these spectral lines, and he set out to do this by assuming that the energy was quantised, and that the orbits of the electron were circular. This explanation is described in his postulates.

This empirical equation for the wavelengths of the hydrogen spectrum therefore led to the development of Bohr’s postulates, from which a theoretical equation may be derived that supports Balmer’s empirical equation.