METAL HALIDE LAMP AND LUMINAIRE USING THE SAME

摘要

The present invention aims at providing a metal halide lamp that (i) prevents a decline in the lumen maintenance and a deterioration of quality in appearance due to the coloring of a casing tube surrounding the arc tube, and at the same time (ii) achieves high luminous efficiency. A metal halide lamp (1) has a pair of electrodes (20a&b) placed in an arc tube (3) made of translucent ceramic, and a sodium halide is enclosed therein. The metal halide lamp (1) satisfies L/D 4, where L (mm) is the length of the space between the electrodes (20a&b) and D (mm) is the internal diameter of the arc tube (3). The metal halide lamp (1) has a casing tube (2) surrounding the arc tube (3), at least around a portion between the electrodes (20a&b). Here, R/r 3.0 is satisfied, where R is the internal diameter of the casing tube (2) and r is the external diameter of the arc tube (3), within a region positionally corresponding to, in a radial direction of the arc tube, the space between the electrodes (20a&b), on a cross-sectional surface where an outer circumference of the arc tube (3) comes closest to the internal circumference of the casing tube (2).