A glow discharge is a plasma formed by the passage of electric current through a low-pressure gas. It is created by applying a voltage between two metal electrodes in a glass tube containing gas. When the voltage exceeds a certain value called the striking voltage, the gas in the tube ionizes, becoming a plasma, and begins conducting electricity, causing it to glow with a colored light. The color depends on the gas used. Glow discharge is widely used as a source of light in devices such as neon lights, fluorescent lamps, and plasma-screen televisions. Analyzing the light produced by spectroscopy can reveal much about the atomic interactions in the gas, so glow discharge is used in plasma physics and analytical chemistry. It is also used in the surface treatment technique called sputtering.