Spectra
The electromagnetic radiation that is emitted from a free atom only occurs at a number of discrete or separate wavelengths or frequencies. This is usually represented as a set of lines.
Visible spectrum of hydrogen spectrum
Interpretation of Spectra
After Einstein, frequency is now linked to energy by E = hf. Each line in the spectra now corresponds to a transition of an electron from one energy level to another level.
In fact, the discrete lines in the spectra must mean that electrons in atoms can only exist at specific energy levels, and the spectral lines represent transitions between these levels.
When an atom is excited electrons are sent to a higher energy level. From there, the electron drops back to the ground state by any of the possible paths, each drop emitting a photon of specific energy and frequency.
That right or completely wrong?