Proper noun
Lyman series
A hydrogen spectral series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1 (where n is the principal quantum number), the lowest energy level of the electron.
Ionization here is due to Lyman series -alpha hydrogen radiation at a wavelength of 121.5 nanometre (nm) ionizing nitric oxide (NO). Source: Internet
The D layer is only present during the day, when some ionization occurs with nitric oxide being ionized by Lyman series -alpha hydrogen radiation. Source: Internet
These photons were from Lyman series transitions, putting them in the ultraviolet (UV) part of the electromagnetic spectrum. Source: Internet