Structure of a neon sign

Neon signs are a variation on the concept of the incandescent bulb. Essentially they are hollow tubes made of lead glass that are filled with a noble gas. Neon was the first gas used; however, it was found that other noble gases such as argon or helium produced markedly different colors when exposed to an electrical current.

How a neon sign works

In a closed environment, a compressed noble gas is relatively inactive. They are called noble gases because they tend not to react with other elements. When introduced to a strong electrical current, electrons passing through the gas don't bind with them, but instead impact and bounce off. This causes the electrons to become excited into a state of greater energy. When they return to their original state, the electrons release photos, which human eyes perceive as light. This light is typically of a very specific wavelength, causing the perception of vivid color for which neon signs are known. The process continues until the electrical current ceases to run through the noble gas.