Demonstration of neon lighting. Footage of examples of neon lighting tubes being tested in a laboratory. The sealed glass tubes have an electrode at each end, and contain a noble gas such as neon, argon or helium. They can also contain hydrogen, carbon dioxide or mercury vapour. When connected to a high-voltage power source, as here, the gas in the tube is ionised and it emits light. The colour of the light depends on the gas or mix of gases being used.