High-Intensity Discharge lamps that produce light from an electric arc in a special medium (a mix of gases and metal salts). These lamps do not have filaments; basically, they produce light by maintaining a continuous spark inside a special bulb. This type of lamp is used for high-output applications. Some examples are cinema projectors, overhead projectors, industrial lighting or car headlights (the so-called xenon bulbs). These require a special electronic ballast to ignite and regulate current inside the lamp.