Fluorescent lamps Fluorescent lamps belong to a group of lighting devices known collectively as discharge tubes. These consist of glass tubes filled with mercury and argon in a gaseous state, with electrodes at either end of the tube. When an electric current is passed through the electrodes, it ionizes the metal vapor which begins to glow, producing light. As in other discharge lamps, a ballast is used to provide the high voltage necessary to ignite the gas. Once the gas has ignited, the fluorescent lamp stabilizes at 100v. The ballast maintains the voltage at a constant level during operation. The light produced by fluorescent lamps is in the ultraviolet range, which is invisible to the human eye, and the inside of the glass tube is coated with a substance that glows when in contact with ultraviolet light, producing visible light.		The main uses of fluorescent lamps in the theatre are to create 'black light' (UV) effect or as a wash for cycloramas. Fluorescent lamps used for black light effects have no inner coating, emitting ultra violet light. The set, props, or costume elements are painted with special paint containing ingredients that transform ultra violet light into visible light. When the stage is darkened the ultra violet light illuminates those elements painted with special 'UV paint', while the rest of the stage remains dark and the light source is not revealed.
		Billy Badd, Geneva Opera.

Neon lights are discharge lamps based on gas contained in a long tube that can be shaped. In theatre these are generally used for effects, such as signs, that are part of the set design. The color of the light is determined by the type of gas filling the tube. For example: neon gas produces red light, helium gas produces white light, and mercury produces blue light. Like other discharge lamps, neon lights are also ignited and operated on high voltage. Control of neon lights is extremely difficult and their ignition is likely to cause disturbances in any sound equipment in proximity to the neon.

A neon strip, Orpheo, The New Israeli Opera.

Certain solid elements, when exposed to a low voltage electric current, react by producing light. These light sources are called light emitting diodes or LEDs, and are used for signal lights on electronic equipment or kinetic effects, such as electronic billboards.