Coldcathode

Coldcathode, in electronics, refers to a type of electron-emitting electrode that does not rely on thermionic heating to emit electrons. In cold-cathode devices, emission is achieved by other mechanisms, most commonly field emission or gas-discharge processes within a sealed tube or envelope. This distinguishes cold cathodes from hot cathodes, which require a heated filament to produce electron emission.

In practice, cold-cathode devices include cold-cathode fluorescent lamps (CCFLs), neon indicators, and vacuum-tube displays such as nixie tubes. In CCFLs, a high-voltage, high-frequency drive ionizes a mercury-vapor gas, and the resulting UV light excites phosphors on the tube walls to emit visible light. The electrical discharge is sustained without a heated filament, and ballast or current-limiting circuitry is required to control current. In neon indicators and nixie tubes, the cathodes are cold and electrons are emitted into a gas-filled envelope, where ionization produces a visible glow.

Compared with hot-cathode devices, cold-cathode systems generally offer longer potential life, simpler cooling needs, and no filament failure but require higher starting voltages and appropriate ballast or regulation. They can be less efficient or have lower brightness at moderate drive levels and can suffer from stability issues at extreme temperatures.

Applications have included backlighting for displays, signage, and decorative or vintage displays. CCFLs were once common for LCD backlights but have largely been supplanted in new designs by LED-based technologies. See also: hot cathode, field emission, nixie tube, neon lamp.