Plasma created by passing an electric current through a low-pressure gas. Ionisation results in the emission of electromagnetic radiation, the spectrum of which depends on the gas used. For example, the glow discharge in hydrogen is pink. It is used in neon lights or fluorescent lamps. In thermonuclear fusion research, glow discharge is used to clean the interior of a chamber, e.g. a tokamak. The glow discharge plasma helps to release impurities from the walls, which are then sucked out by a vacuum pump.