What is a Nixie tube?

A Nixie tube is an electronic device for displaying numerals or other information. Although the term “Nixie” is a trademark, it has come into the English language as a generic term for cold-cathode gas-discharge numerical and symbol indicator tubes.

A Nixie tube consists of a glass tube containing a wire-mesh anode and multiple cathodes shaped like numerals or other symbols. The most common form of Nixie tube has ten cathodes in the shapes of the numerals 0 to 9, but there are also types that show various letters, signs and symbols. The tube is filled with a mixture of gases, mostly neon.

Each cathode can be illuminated by applying about 170 volts DC at a few milliamperes between the cathode and the anode. This ionizes the gas around the cathode, causing it to glow in the characteristic neon red-orange color.

Unlike vacuum tubes used in old radios and TVs, which require a filament to heat the cathode, Nixies have no filament and generate almost no heat. That is why they are called cold-cathode tubes.

Because the numbers and other characters are arranged one behind another, each character appears at a different depth, giving Nixie-based displays a distinctive appearance. Some Russian Nixies, e.g. the IN-14, used an upside-down digit 2 as the digit 5, presumably to save manufacturing costs as there is no obvious technical or aesthetic reason.

Nixie displays were introduced in 1955 by Burroughs Corporation. The name Nixie was derived by Burroughs from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1." Though Burroughs filed for trademark status of the Nixie term in 1956, “Nixie” has since become a generic term for this type of display.

Nixies were used as numeric displays in early digital voltmeters, multimeters, frequency counters and many other types of technical equipment. They also appeared in many early electronic desktop calculators. Some elevators used Nixies to display floor numbers. Nixie tubes are no longer manufactured, but they were made in large quantities from the 1950s until the late 1970s, when they were supplanted by 7-segment LED displays.