Patent ID: 9431232
Filing Date: 2016-08-30
CPC Classification: H01J

Claim Text:
1. A short arc discharge lamp comprising: an arc tube configured to enclose a light emitting gas; a cathode disposed in the arc tube; and an anode disposed in the arc tube such that the anode and the cathode face each other in the arc tube, the cathode comprising an electron emitting section made from tungsten to which thorium is added, and an electrode body section made from tungsten to which thorium is not added, the electrode body section being provided with a recess portion at a front end side of the electrode body section, and the electron emitting section having a circular truncated conical shape, a rear end side of the electron emitting section being received in the recess portion and a front end side of the electron emitting section protruding from the recess portion, wherein the electrode body section is provided with an annular flat surface portion at an opening surface of the recess portion, and a step is formed by the annular flat surface portion and the electron emitting section; wherein a percentage of a width of the annular flat surface portion to a diameter of a cylindrical lateral surface portion of the electron emitting section is set to 16% or more.