Gas discharge tube having precise electrode arrangement

A gas discharge tube having a sealed envelope at least a part of which transmits light, said sealed envelope being filled with a gas and being provided with anode and cathode sections disposed therein, electric discharge being generated between said anode and cathode sections, so that the light-transmitting part of said sealed envelope emits predetermined light outside;

• said gas discharge tube comprising:
• an insulating anode support member mounting said anode section;
• an insulating focusing electrode support member, mounted on a surface of said anode support member surrounding said anode section, having an opening on said anode section;
• and
• a focusing electrode, securely disposed at a front face of said opening of said focusing electrode support member, having a focusing opening projecting toward said anode section,
• wherein said cathode section is disposed on said anode support member or focusing electrode support member so as to be spaced from said focusing opening, at least one of said anode support member and focusing electrode support member having a portion with a shape fitting with side walls of said anode section so as to secure said anode section in a fixed position.