It says it is transparent because visible light has energies from 1.8 to 3.1eV, and in order to move a Hydrogen atom from ground state to the first excited state, requires 10.2eV.
I read online that if a current is passed through a container of hydrogen, some light is emitted, and if this light emitted is put through a prism, 4 bands of light are observed.
So say, instead, only UV light was passed through a container of hydrogen gas, would any atoms rise energy levels? UV light has energy of 100 eV, so this is enough energy, but I could not find anything on the internet about this. What color would this light emitted be, if any light was emitted?