| 摘要 |
PURPOSE:To enhance the efficiency of a lamp together with reduction of deviation from its luminous color, by covering a part of a luminous tube with a transparent and heat insulating member of a specific size as well as providing in vacuum inside an outer tube. CONSTITUTION:The upper end of a heat insulating member 11 made of transparent material is located above the highest position inside a luminous tube 1 and a distance between the lower end of the heat insulating member 11 and tip A of a main electrode located downward therefrom is set less than one third of a distance between both main electrodes. And the lower end of said heat insulating material 11 is positioned above the middle point between the tip A of the main electrode located below and the lowest portion B in side the luminous tube 1. Since a temperature higher than the temperature at the lower end part of the luminous tube is set to other portions and consequently not yet evaporated metallic halide is gethered in a narrow area at the lower end part of the luminous tube, the vapor pressure of the metallic halide is determined by only the temperature at said lower end part. Resultantly, deviation in luminous color is reduced, the temperature is raised at the lower end part of the luminous tube due to reflection of a part of light and infrared rays reflected by the heat insulating member, thus the efficiency of a lamp can be enhanced due to no attenuation of luminescence owing to transparency of the heat insulating member.
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