Neon lamp

A neon lamp is a gas release lamp containing neon gas (or in types with different colors also other noble gas) at low pressure. A small electric current, which may be AC or DC, is passed during the tube, causing it to glow orange-red. In AC-excited lamps, both electrodes create light, but in a DC-excited lamp, only the negative electrode glows. This simple fact can be used to differentiate between AC and DC sources using a neon lamp and to distinguish the polarity of DC sources.

Small neon lamps are used as indicators in electronic tools. Larger lamps are used in neon signage. Because of their moderately fast response time, in the early development of television, neon lamps were used as the light source in many mechanical-scan TV displays.

Most small neon (indicator-sized) lamps start conducting at a rather consistent 60 to 80 volts, so they were used as very simple voltage regulators or over voltage protection devices. They were also used for a selection of other purposes; since a neon lamp can act as a relaxation oscillator with an added resistor and capacitor, it can be used as a simple flashing lamp or audio oscillator. In the 1960s General Electric (GE), Signalite, and other firms made special extra-stable neon lamps for electronic uses. They still devised digital logic circuits, binary memories, and frequency dividers using neons. Such circuits appeared in electronic organs of the 1950s, as well as several instrumentation.

Neon lamps are negative resistance devices where raising the current flow through the device increases the number of ions, thereby decreasing the resistance of the lamp, thereby allowing increased current run. Because of this, the electrical circuitry external to the neon lamp must provide a means to limit the current flow in the circuit or else the current will increase pending the neon lamp destroys itself. For indicator-sized lamps, a resistor is conventionally used to boundary the current flow. For sign-sized lamps, the high voltage transformer usually limits the obtainable current, often by its having a large amount of leakage inductance in the secondary winding.

Indicator-sized lamps can also be packed with argon or xenon rather than neon, or mixed with it. While most operating characteristics remain similar, the lamps light with a bluish glow (including some ultraviolet) rather than neon's characteristic reddish-orange glow; the UV radiation then can be used to excite a phosphor coating of the within of the bulb and provide a wide range of various colors, including white. A mixture of neon and krypton can be used for green glow.

Neon lamps, due to their short current consumption, are good as nightlights.

A helium-neon laser is a far-away cousin of a neon lamp.

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