text: Helium is in the same category as alkaline earths with respect to spectroscopy, as it has two electrons in the S subshell as do the other alkaline earths.
  Helium has a diffuse series of doublet lines with wavelengths 5876, 4472 and 4026 Å. Helium when ionised is termed He and has a spectrum very similar to hydrogen but shifted to shorter wavelengths. This has a diffuse series as well with wavelengths at 6678, 4922 and 4388 Å.