What are neon lights?
A light using two (or more) electrodes in a glass tube filled with a mixture of inert gases. The most common (and the source of the name) is neon gas, which produces a red light when ionized by current flow between the electrodes. Helium, argon, and xenon are used in the mixture to produce other colors. Sometimes neon lights have a tiny amount of tritium gas added because the radioactivity pre-ionizes a little of the inert gas making it easier to start current flow to ionize the rest of the gas and produce light.
One type of neon light used in older electronic equipment that displayed numbers called a Nixie tube typically had 12 electrodes in a cylindrical glass tube: one electrode was common, ten of the electrodes were shaped like the digits 0 to 9, and the last electrode was a decimal point.