| 摘要 |
PROBLEM TO BE SOLVED: To suppress cathode consumption at a lighting time, provided a sufficient light output and stability, and extend a lamp life by establishing specific relationship among a cathode tapered tip angle, a cathode tapered tip portion surface area, cathode axis current density, and a life time. SOLUTION: Both of following expression are to be satisfied. 20<(J.H)/θ<80, and 0<S<0.5, where θ deg. is a cathode tapered tip angle, S mm<2> is a cathode tapered tip portion surface area, JA/mm<2> is cathode axis current density, and H hours are a life time. In a dc lighting type high pressure mercury discharge lamp 1, a bulb 2, being an air tight vessel, is formed by integrally continuously forming of a main body portion 2a which is an elliptical rotation body-like discharge space portion made of translucent quartz glass, and one pair of sealing portions 2b, 2c which are formed by crushing in the diameter direction at both ends of the long span thereof. A cathode 4 and an anode 3 are made of high melting point metal such as tungsten or the like, and the respective base end portions thereof are conductive body foils embedded in the respective sealing portions 2b, 2c and are electrically connected to molybdenum foils 5a, 5b. |
