Patent ID: 7021985

Claim:
A manufacturing method for an arc tube formed by turning a glass tube at a substantially middle thereof and winding the glass tube from the middle to both ends thereof around an axis to form a double spiral, and sealing a pair of electrodes at both the ends of the glass tube, the manufacturing method comprising the steps of: winding the glass tube that is softened by heating, along a groove in a double spiral formed on an outer circumference of a mandrel; removing the glass tube that is wound in a double spiral from the mandrel; making a pitch of (a) a spiral part in a vicinity of a sealing part at each end of the glass tube and (b) an adjacent spiral part in a direction of the axis, larger than a pitch of other adjacent spiral parts, to widen a gap between the sealing part and the adjacent spiral part; and pinch-sealing the electrodes in the sealing parts at both the ends of the glass tube.