A gas discharge lamp is a lamp that emits light by discharging a mixture of gas, metal vapor, or several gases with metal vapor. An electrical source that converts electrical energy into light by gaseous discharge. There are many kinds of gas discharge, and glow discharge and arc discharge (see arc discharge) are widely used. Glow discharge is commonly used in neon and indicator lights. Arc discharge can have very strong light output, lighting source USES arc discharge. Fluorescent lamps, high-pressure mercury vapor lamps, sodium lamps and metal halide lamps are the most widely used discharge lamps for lighting purposes.