A metal halide lamp has an arc tube including an arc tube container made
of an oxide-based translucent ceramic material. The arc tube is filled
with cerium halide as a luminescent material and a halide of a rare earth
element that is more reactive with the ceramic material than is the
cerium halide. Accordingly, a reaction between the oxide-based
translucent ceramic material and the halide of a rare earth element is
accelerated while a reaction between the oxide-based translucent ceramic
material and the cerium halide is suppressed. This suppresses a decrease
of the cerium halide that serves for light emission, and also reduces
changes in the lamp color temperature. Thereby, during aging of the lamp,
the flux maintenance factor and color temperature are improved.
Therefore, the indoor-outdoor metal halide lamp provides a white light
source color that has high-wattage, high luminous efficiency, and a long
service life.