Lyman Limit
A specific wavelength (91.2 nm) that corresponds to the energy needed to ionize a hydrogen atom (13.6 eV). Galactic space is opaque at wavelengths shorter than the Lyman limit.
High-redshift galaxies can now be identified wholesale by a particularly simple kind of photometric redshift, using that fact that any non-AGN galaxy goes black at the Lyman limit (912 Å).
(b) The spectral series of the hydrogen atom associated with the first energy level or ground state. The series lies in the ultraviolet (L at 1215.67 Å; L at 1026 Å). The series limit is at 912 Å. (He II L, 303.78 Å; He II Lyman limit, 227 Å.) ...
 See also: Light, Energy, Field, Galaxy, Luminosity
  
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