= Lyman series
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The <Lyman series> consists of hydrogen transitions terminating in the $n=1$ <ground state>. Its emission wavelengths obey $1/\lambda=R_H(1-1/n_i^2)$ for $n_i=2,3,\ldots$. The $2p\to1s$ electric-dipole line is the <Lyman-alpha line>, and the accumulation point is the <Lyman limit>.
These larger energy differences put the series in the <ultraviolet> rather than the visible Balmer range. Observing it requires suitable ultraviolet optics and a detector whose response includes those wavelengths; ordinary visible-light transmission is not sufficient.
As the upper level approaches the ionization threshold, the lines crowd together. Above that threshold, absorption from the ground state can ionize the atom instead of producing a higher discrete bound level. The <Rydberg formula> describes the line positions, while populations, radiation transport and instrumental resolution determine which lines are distinguishable.
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