What we have said about the atomic spectrum of hydrogen holds for other elements as well. Every chemical element, when heated to an incandescent gas, emits radiation at a particular set of frequencies, which is just as characteristic of the elements as are the fingerprints of a person. This is the element's atomic emission spectrum.

Conversely, if radiation of all wavelengths is passed through a somewhat cooler atomic gas of an element, the gas can absorb or remove radiation at the same set of frequencies, to produce an atomic absorption spectrum. These frequencies, which represent transitions between quantum levels of the atom, can be used to construct an energy-level diagram for that kind of atom.