| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain high luminous efficiency, and prevent dropping of lumen maintenance factor or falling of appearance quality by an outer tube, a sleeve or the like surrounding an arc tube being colored. <P>SOLUTION: A pair of electrodes 20a, 20b are arranged inside an arc tube 3 with its envelope made of translucent ceramic, and also, halide of sodium is enclosed. When an inner diameter of the arc tube 3 is represented as D(mm), and a distance between electrodes 20a, 20b is represented as L(mm), a formula L/D≥4 is satisfied. Tubular bodies 2, 31 arranged to surround a part at least including the distance L between a pair of electrodes 20a, 20b in a discharging space of the arc tube 3 is included on an outside of the arc tube 3. In the arc tube 3 between a part passing the distance L between the pair of the electrodes 20a, 20b and the tubular bodies 2, 31, an outer diameter of the arc tube 3 in a part where each of them comes closest, is represented as r(mm), and an inner diameter of the tubular bodies 2, 31 is represented as R(mm), a formula R/r≥3.0 is satisfied. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
