Metal halide lamp with stabilized lamp lighting

摘要

It is an object of the present invention to provide a metal halide lamp in which arc discharge in the initial stage of lamp lighting can be stabilized. A metal halide lamp includes a translucent outer tube with a base formed at one end thereof and a light-emitting portion disposed in the outer tube. This metal halide lamp is configured as a vertical mounting type such that the base thereof looks toward the upper side. The discharge tube has mercury and metal halides enclosed therein. Assuming that a lamp rated power is P [W], then a mercury concentration d(Hg) [mumol/cm3] in the discharge tube falls within a range of values of ±10% of a mercury concentration d(Hg) obtained by the following equation "d(Hg)=0.0007P2-0.4113P+99.557".