Patent ID: 7557509

Claim:
A gas discharge tube comprising: a sealed vessel in which gas is encapsulated; a cathode section arranged in said sealed vessel; an anode section, arranged in said sealed vessel, for generating discharge between said anode section and said cathode section; and a discharge path restricting section, arranged in said sealed vessel, having a single hole for narrowing a discharge path between said cathode section and said anode section, wherein said anode section has a first surface facing said discharge path restricting section, a second surface opposing said first surface, and a single opening portion for communicating between said first surface and said second surface, said single opening portion provided so as to correspond one-to-one with said single hole of said discharge path restricting section, wherein a cross section of said single opening portion defined on a first reference plane coincident with said first surface has a non-circular shape, and wherein said entire single hole is included in said single opening portion, when viewing said single hole through said single opening portion along an optical axis of light to be emitted from said gas discharge tube.