Dimmable metal halide lamp and lighting method

摘要

A metal halide lamp in which an arc tube is housed within a bulb having a base at one end thereof. The arc tube includes a main tube, two thin tubes that extend one from each end of the main tube, and a pair of electrode inductors. The main tube and the thin tubes are made from translucent polycrystalline alumina and constitute a discharge vessel having a discharge space therein. Lamp power under dimming conditions is set in a range defined by maximum lamp power Wmax [W] and minimum lamp power Wmin [W], with a surface area S [cm<2>] of the inner surface of the discharge vessel satisfying Wmax/60<=S<=Wmin/20.