Neon glow lamp

(electronics) A glow lamp containing neon gas, usually rated between ½5; and 3 watts, and producing a characteristic red glow; used as an indicator light and electronic circuit component.

A low-wattage lamp often used as an indicator light or as an electronic circuit component. The neon lamp usually consists of a pair of electrodes sealed within a bulb containing neon gas at a low pressure. Some of the smaller bulbs are equipped with wire leads that are connected directly into the electrical supply circuit; others are equipped with conventional bases that vary with the size of the lamps (see illustration).

Some examples of glow lamps.

Electrodes sealed in a neon atmosphere will emit electrons if a sufficient voltage difference is impressed across them. In glow lamps the electrodes are usually treated to emit electrons freely. With a sufficiently high voltage between electrodes, the velocity of electron flow is high enough to ionize the neon nearest the negative electrode (cathode). The neon then emits a reddish-orange glow similar to the color of neon sign tubing. With direct current the glow is restricted to the immediate vicinity of the negative electrode. With alternating current, both electrodes act alternately as cathodes, and the glow appears alternately at both surfaces. At usual frequencies, the alternations occur so rapidly that both electrodes appear to glow constantly. In dc circuits, the voltage across the electrodes may be reduced significantly, once the lamp has started, without causing the lamp to go out.