upper limit photon energy

[acherentia]

why is there an upper limit to the photon energy that can be observed in the emission spectrum of the hydrogen atom?

[Petr Mugver]

Because it corresponds to the difference of energy of the most energetic bound state of H, which is 0, and the ground state energy, which is a certain negative amount that I don't remember, something like 10 eV.

[Eudoxie]

The ionization energy is 13.6 eV. Which corresponds to the light emitted by a H+ ion that absorbs an electron which drops immediately to ground state.