- Lines in the spectrum caused by transitions between the various possible locations for the electron of a hydrogen atom. There are several series of hydrogen lines, each known by the name of a scientist involved in their elucidation. The first is the Lyman series, which involves transitions between the ground state and the five excited states above it, and which are observed in the ultraviolet. The Balmer series involves transitions between the first excited level and the four above it and is observable in visible light (hydrogen alpha). In the infrared come the Paschen and Brackett series, which are produced by transitions to and from the second and third excitement states from above.