Caption: A diagram illustrating the image line spectrum of hydrogen (i.e., the (neutral) atomic hydrogen spectral series) shown on a logarithmic scale for wavelength.

The hydrogen spectral series are observed when electromagnetic radiation (EMR) from a dilute neutral atomic hydrogen gas dispersed into what is called a line spectrum.

The atomic hydrogen spectral series are detailed in below in Table: Atomic Hydrogen Spectral Series.

Table: Atomic Hydrogen Spectral Series

1. Lyman series (Ly) n ≥ 2 → 1 transitions
2. Balmer series (Ba) n ≥ 3 → 2 transitions
   1. Hα n=3 → 2, λ=6562.80 Å, E=1.8886 ... eV
   2. Hβ n=4 → 2, λ=4861.32 Å, E=2.5496 ... eV
   3. Hγ n=5 → 2, λ=4340.46 Å, E=2.8556 ... eV
   4. Hδ n=6 → 2, λ=4101.73 Å, E=3.0218 ... eV
   5. Hε n=7 → 2, λ=3970.07 Å, E=3.1220 ... eV
   6. Balmer limit n=∞ → 2, λ=3464 Å, E=3.4014 ... eV
3. Paschen series (Pa) n ≥ 4 → 3 transitions
4. Brackett series (Br) n ≥ 5 → 4 transitions
5. Pfund series (Pf) n ≥ 6 → 5 transitions
6. Humphreys series (Hu) n ≥ 7 → 6 transitions
7. No name series n ≥ 8 → n ≥ 7 transitions

Note that (neutral) atomic hydrogen lines occur in the ultraviolet band (fiducial range 0.01--0.4 μm), visible band (fiducial range 0.4--0.7 μm), infrared band (fiducial range 0.7 μm -- 0.1 cm), and radio band (fiducial range 3 Hz -- 300 GHz = 0.3 THz, 10**6 nm = 0.1 cm -- 10**5 km). The ordinary hydrogen spectral series has only been found experimentally to the infrared band (fiducial range 0.7 μm -- 0.1 cm) (see Wikipedia: Hydrogen spectral series: Further series (n' > 6)), but the hydrogen 21-centimeter line (arising from the hyperfine structure of the hydrogen ground state) is in the radio band (fiducial range 3 Hz -- 300 GHz = 0.3 THz, 10**6 nm = 0.1 cm -- 10**5 km).

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