Cold cathode

A cold-cathode vacuum tube does not rely on external heating of an electrode to provide thermionic emission of electrons.

Neon lamps are used both to produce light as indicators and for special-purpose illumination, and also as circuit elements displaying negative resistance.

The flash tube is a cold-cathode device filled with xenon gas, used to produce an intense short pulse of light for photography or to act as a stroboscope to examine the motion of moving parts.

Cold-cathode fluorescent lamps were used for backlighting of LCDs, for example computer monitors and television screens.

In the lighting industry, “cold cathode” historically refers to luminous tubing larger than 20 mm in diameter and operating on a current of 120 to 240 milliamperes.

[3][4] The term "neon lamp" refers to tubing that is smaller than 15 mm in diameter[citation needed] and typically operates at approximately 40 milliamperes.

The surface of cold cathodes can emit secondary electrons at a ratio greater than unity (breakdown).

Cold-cathode devices typically use a complex high-voltage power supply with some mechanism for limiting current.

A common cold-cathode application is in neon signs and other locations where the ambient temperature is likely to drop well below freezing, The Clock Tower, Palace of Westminster (Big Ben) uses cold-cathode lighting behind the clock faces where continual striking and failure to strike in cold weather would be undesirable.

Large cold-cathode fluorescent lamps (CCFLs) have been produced in the past and are still used today when shaped, long-life linear light sources are required.

CCFL lifespans vary in LCD televisions depending on transient voltage surges and temperature levels in usage environments.

However, CCFLs are strictly limited in the degree to which they can be dimmed, both because a lower plasma current will lower the temperature of the cathode, causing erratic operation, and because running the cathode at too low a temperature drastically shortens the life of the lamps.

[citation needed] Much research is being directed to this problem, but high-end manufacturers are now turning to high-efficiency white LEDs as a better solution.