| 摘要 |
Provided is a manufacturing method of an arc tube including a flat-spiral glass tube, the manufacturing method having: a first step of forming a glass tube into a substantially circular cone shape, by winding the glass tube in softened state to a conical surface of a jig; and a second step of flattening the circular-cone-shaped glass tube into a substantially disc shape, where a distance Gb1 is substantially uniform, where the distance Gb1 is measured in a parallel direction to a plane including substantial part of the tubular axis of the disc-shaped glass tube and is between adjacent exterior walls of the circular-cone-shaped glass tube respectively belonging to: a first substantial part of a first-flat-spiral-portion scheduled portion; and a second substantial part of a second-flat-spiral-portion scheduled portion, and a distance Ge1 is longer than the distance Gb1, where the distance Ge1 is measured in the parallel direction to the plane and is: between adjacent exterior walls of the circular-cone-shaped glass tube respectively belonging to the second-flat-spiral-portion scheduled portion and a first-end-portion scheduled portion; and between adjacent exterior walls of the circular-cone-shaped glass tube respectively belonging to the first-flat-spiral-portion scheduled portion and a second-end-portion scheduled portion.
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