| 摘要 |
PROBLEM TO BE SOLVED: To provide a direct-current discharge lamp having a small fusion loss or deformation of a cathode head, even if a cathode luminescent spot having high luminance is obtained by increasing a current density at the cathode head, and having the luminance or the position of the cathode luminescent spot, stabilized for long hours, and a long lamp life. SOLUTION: In this direct-current discharge lamp in which a cathode 21 and an anode 22, composed of tungsten, are arranged oppositely in an arc tube 11, and an emitter, composed of a single substance of a barium oxide or a calcium oxide or a strontium oxide or of a sintered body of tungsten powder including a complex thereof, is arranged on the head of the cathode 21, the volume of the cathode 21 is set as 70-200% of the volume of the anode 22.
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