A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies.

How are spectral lines created?

Spectral lines are produced by transitions of electrons within atoms or ions. As the electrons move closer to or farther from the nucleus of an atom (or of an ion), energy in the form of light (or other radiation) is emitted or absorbed.…

How do you find a spectral line?

For example, suppose one atom with an electron at energy level 7 (n2=7). That electron can "de-excite" from n2=7 to n1=6,5,4,3,2, or 1. All those transitions give one spectral line for each. Thus, total of 1×6=n1(n2−n1) (foot note 1) spectral lines would be present in the spectrum.