Neon light
A neon lamp is a gas-discharge tube containing neon gas at low pressure. A small electric current, which may be AC or DC, is passed through the tube, causing it to glow orange-red. In AC-excited lamps, both electrodes produce light, but in a DC-excited lamp, only one electrode glows. This simple fact can be used to distinguish between AC and DC sources using a neon lamp.
Small neon lamps are used as indicators in electronic equipment. Larger lamps are used in neon signage.
Most neon lamps start conducting at a fairly consistent 60 to 80 volts, so they were used as very simple voltage regulators. They were also used for a variety 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 GE and other firms made special extra-stable neon lamps for electronic uses. They even devised digital logic circuits, binary memories, and frequency dividers using neons. Such circuits appeared in electronic organs of the 1950s, as well as some instrumentation.
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