| 摘要 |
PURPOSE:To prevent any reduction of lamp voltage, luminance or optical spectra from occuring even when the orientation of a short-arc-type metal halide lamp (in which a heat insulating film is formed only on one end of the bulb) during lighting is arbitrarily changed by shifting the center of the interelectrode distance toward the bulb end having no heat insulating films. CONSTITUTION:When the heat insulating film of an end of a short-arc-type metal halide lamp which is located near the reflection mirror 7 of a planetarium is removed, it is possible to effectively utilize light discharged toward one side of the lamp since the light-shielding effect of the heat insulating film does not exist. However, when the lamp is ignited with its end from which the heat insulating film is removed directed downward, the effect of the heat insulating film increasing the temperature of the bulb wall decreases thereby resulting in a reduction of lamp voltage and a decrease of luminous flux. In this invention, the interelectrode center is shifted to the end from which the heat insulating film is removed by a distance of delta, so that this end is warmed by arc to accelerate the evaporation of a metal halide and increase the vapor pressure thereby enabling the lamp voltage and the luminous flux to be increased. When the interelectrode distance (l) is adjusted to be the same as that of the conventional lamp, the distance between the root of the fusing area of the electrode and the center line (X-X) entending along the axis of the bulb 10 is supposed to be (l1) and the distance between the line (X-X) and the line (Y-Y) is supposed to be delta, it is recommended to adjust the delta/l1 ratio to 0.05-0.3. |
