The glow lamp, like the fluorescent lamp, is a gas discharge lamp. A high voltage of around 70V is applied to it, which leads to the ionization of the noble gas atoms inside the lamp. This is called shock ionization. The charge carriers that are released look for new locations in the atoms and release the energy they have absorbed in the form of light; they recombine. In order to prevent the atoms from reacting further, noble gases are used in gas discharge lamps. The luminous phenomenon can always be observed at the cathode. When there is alternating voltage, both electrodes light up.