Cold cathode

A cold cathode^[1] is a cathode that is not electrically heated by a filament.^{[note 1]} A cathode may be considered "cold" if it emits more electrons than can be supplied by thermionic emission alone. It is used in gas-discharge lamps, such as neon lamps, discharge tubes, and some types of vacuum tube. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament. A cold cathode does not necessarily operate at a low temperature: it is often heated to its operating temperature by other methods, such as the current passing from the cathode into the gas.

This article is about light sources and indicators. For cold cathode ion sources, see Ion source.