Neon Technology
Neon (symbol Ne) produces a glow in a vacuum electric-discharge tube and is used extensively in the familiar advertising displays.
A neon light is a glass bulb or tube containing neon (gaseous element) at low pressure, and two metallic electrodes. To make a neon light, the tube is bent while warmed, to the desired shape and sealed at both ends. During the sealing process, electrodes are added at each end. An access port is left near one end and a vacuum is applied to the interior of the tube. After the air and humidity has been removed, the neon gas is added under low pressure and the tube is sealed.
The light produces a reddish-orange glow when an electric current (applied across the electrodes) is raised in voltage to the point at which it ionizes the gas in the tube. The voltage at which the light glows varies with the design of the tube. When the glass tube is ionized, the voltage drop across the tube is constant, regardless of the amount of current flowing through the tube. The neon glows with an even intensity throughout the length of the tube.
A variant of this is the glass tube containing ionized neon at very low pressure. The tube shines with a brilliant red glow if a high-voltage alternating current is applied to the electrodes sealed in the ends of the tube.