Wiktionary
discharge tube
n. (context physics English) Any device in which a flow of electrons (or ions) through a gas acts as a source of light
Usage examples of "discharge tube".
There was a deafening report as the lantern's discharge tube exploded.
Toward the middle of their visit to the seventh fort, Ursis had used The Manuals to trace energy channels within one of the disruptors back from its discharge tube.
It found the source easily, warm water coming out of a discharge tube.