Patent ID: 7348730

Claim:
A metal halide lamp comprising: an arc tube made of translucent ceramic and having a main tube part in which a pair of electrodes are disposed; and an outer tube housing the arc tube therein, wherein 4.0≦L/D≧10.0, where L is a length of space between the electrodes and D is an internal diameter of the main tube part, 3.4≦R/r≦7.0, where R is an internal diameter of the outer tube and r is an external diameter of the main tube part, within a region positionally corresponding to, in a radial direction of the outer tube and the arc tube, the space between the electrodes, on a cross-sectional surface where an outer circumference of the arc tube comes closest to an inner circumference of the outer tube, and M≦4.0, where M (mg/cc) is a density of mercury enclosed in the arc tube.