Which noble gas is used in neon signs?

The noble gas used in classic neon signs is neon.

A neon tube is a sealed glass tube containing a low-pressure gas. When a high voltage is applied, the gas becomes electrically excited and emits light. Pure neon produces its famous bright orange-red glow, which is why the signs and the lighting technology took neon’s name. The element neon was discovered in 1898 by British chemists William Ramsay and Morris Travers while they were examining gases separated from the atmosphere.

The phrase “neon sign” can cause a technical mix-up. Many commercial signs that look like neon use other gases, colored glass, or fluorescent coatings. Argon, often combined with mercury vapor, can create ultraviolet light that activates a phosphor coating; other gases can produce colors such as yellow, pink, or purple-red. These are still broadly called neon lighting, even though the glowing gas is not always neon.

Neon signs became commercially important after Georges Claude developed practical neon-tube lighting and patented related electrode technology in 1915. They became especially associated with advertising from the 1920s onward. Neon is chemically inert under ordinary conditions, but its excited atoms readily release visible light in a discharge tube.