| 摘要 |
PURPOSE: To improve the efficiency of emission by causing infrared ray emitted from a filament to be reflected by an infrared reflection film provided on an approximately spheroidal part joined to a reduced-diameter part. CONSTITUTION: A filament 1 has a multiple coil part 1a and legs 1c, 1c at both ends of the multiple coil part 1a, the multiple coil part 1a having a length that almost stretches between the first focal point F1 and second focal point F2 of an approximately ellipsoid of revolution part 2d. A light transmissive airtight container 2 includes the approximately spheroidal part 2d provided in such a way as to surround the multiple coil part 1a, with the axis of the multiple coil part 1a roughly placed on the major axis of the ellipsoid of revolution part 2d, and a reduced-diameter part 2c joined to one end of the approximately ellipsoid of revolution part 2d. An angleθfrom near a side end 1d of the reduced-diameter part 2c to the outer surface of the reduced-diameter part 2c is 170 deg. or less, and an infrared reflection film 3 is provided on the surface of the approximately ellipsoid of revolution part 2d, whereby the efficiency of emission can be enhanced.
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