A cold cathode is a cathode that is not electrically heated by a filament. 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.
A set of cold cathode discharge tubes
The stacked digit arrangement in a Nixie tube is visible here
A standard computer case fitted with blue and green cold-cathode tubes
Cold-cathode fluorescent lamp backlight
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma.
Germicidal lamps are simple low-pressure mercury vapor discharges in a fused quartz envelope.
Jules Verne's "Ruhmkorff lamp"
A compact fluorescent lamp
15 kW xenon short-arc lamp used in IMAX projectors