| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide such a structure that can prevent blackening of the inner wall of a luminous tube, by shifting an arc origin quickly to the tip side of a tip portion, even if arc is generated at a discharge origin on the outer periphery of the joint surface of the body and the tip portion, at startup of a long arc discharge lamp including a luminous tube, and a pair of electrodes arranged to face each other in the luminous tube, and having such a structure that a tip portion composed of tungsten containing emitter is joined to the apical surface of a body composed of tungsten.SOLUTION: A luminous tube has a diameter decreasing gradually from a position corresponding to the tip of an electrode toward a sealing portion, and a portion of the electrode corresponding to the joint surface of the body and tip portion of the electrode has a diameter smaller than that in the central part of the luminous tube.</p> |
