I learned that a hydrogen lamp emits photons at specific spectral lines because of electrons falling from a higher energy level to a lower energy level.
I think I understand this.
However, nowhere can I find an explanation of the following, deeper, questions:
Isn't the hydrogen electron sitting at the lowest energy level and therefore it first needs to be brought up to a higher energy level? Is this achieved with the higher voltage? If so, why is the voltage resulting in this? Is there an electron flow from plus to minus when the voltage is applied?
I think that if the voltage brings the electrons to a higher level, then the voltage needs to disappear so that they can fall back and photons are being transmitted. This leads me to believe that we need AC current for this, which results in a periodic change of the energy levels of the electrons, and thus a periodic emission of photons - is that correct? So this would not work with DC?