Neon lamp
Neon lamps are small bulbs filled with neon and used as indicator bulbs producing a orange/red glow. This is not to be confused with neon signage. Neon lamps, in general, consist of a gas-discharge tube containing neon at low pressure and, when electified by alternating currents a luminescence is produced by the action of currents at high frequencies that are around the tube.A neon lamp can be exited by AC or DC. In AC exited lamps, both electrodes produce light and glow, but in a DC exited lamp, only one electrode glows. This simple fact can be used to distinguish between AC and DC sources using a neon lamp.
In addition to many other uses they were used as very simple voltage regulators in the days of tube electronics. Neon lamps were also used for a variety of other purposes in olden times. A good set of links describing those is :
See also: Timeline of lighting technology, Neon, 1911 in science, Neon signage
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