Abstract: 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.

Abstract: he present invention aims at providing a metal halide lamp having a configuration to achieve the following goals: to prevent the lamp from burning out during the life due to a rise in lamp voltage; and to obtain high luminous efficiency at the same time. The metal halide lamp 1 comprises: an arc tube 4 made of translucent ceramic and having a main tube part 6 in which a pair of electrodes 14 is disposed; and an outer tube 3 housing the arc tube 4 therein. 4.0?L/D?10.0, where L (mm) is a length of a space between the electrodes 14 and D (mm) is an internal diameter of the main tube part 6. R/r ?3.4, where R (mm) is an internal diameter of the outer tube 3 and r (mm) is an external diameter in the main tube part 6 of the arc tube 4, within a region positionally corresponding to, in a radial direction of the outer tube and the arc tube, the space between the electrodes 14, on a cross-sectional surface where an outer circumference of the arc tube 4 comes closest to an inner circumference of the outer tube 3. M?4.

Abstract: A metal halide lamp of the present invention has an arc tube formed of ceramic and a pair of opposing electrodes. This lamp includes a Pr (praseodymium) halide, a Na (sodium) halide, and a Ca (calcium) halide enclosed within the arc tube. The Pr halide content Hp [mol], the Na halide content Hn [mol], and the Ca halide content Hc [mol] satisfy the relationships of 0.4?Hc/Hp?15.0 and 3.0?Hn/Hp?=25.0.

Abstract: A high pressure discharge lamp includes an outer tubular bulb whose inner space is exhausted to a vacuum; an arc tube contained in the outer tubular bulb; and a voltage reducing switching element for reducing a voltage applied to the arc tube. The voltage reducing switching element includes a heat sensitive switching element and a starting-voltage reducing element which are connected in series. During a period in which the heat sensitive switching element has a predetermined temperature or higher, the heat sensitive switching element is closed to electrically connect the arc tube and the voltage reducing switching element in parallel, so that the starting-voltage reducing element is operated. During a period in which the heat sensitive switching element has a temperature lower than the predetermined temperature, the heat sensitive switching element is opened so that the starting-voltage reducing element is not operated.

Abstract: A metal halide lamp that includes an arc tube having an envelope made of translucent ceramic and a pair of electrodes disposed in the envelope, wherein a sodium (Na) halide, a mercury (Hg) halide, and one or more lanthanide halides are enclosed within the arc tube, the lanthanide halides including at least one of a cerium (Ce) halide and a praseodymium (Pr) halide, and L/D?1, where D (mm) is an inside diameter of the arc tube, and L (mm) is a distance between the electrodes.