Patent ID: 8247974

Claim:
A high pressure discharge lamp comprising: an arc tube that includes: a light-emitting part having a substantially spherical shape and having mercury enclosed therein; and a pair of sealing parts extending from opposite sides of the light-emitting part; and a pair of electrodes that are arranged in the arc tube such that an end of each electrode is sealed by a respective sealing part and the other ends of the electrodes oppose each other in the light-emitting part, wherein the enclosed mercury has a density of 0.2 to 0.4 [mg/mm3] inclusive, a distance W from a contact point S to a center O of the light-emitting part is 3.0 to 5.0 [mm] inclusive, where the contact point S represents a point where a tube axis Z of the arc tube intersects with an inner surface of the arc tube, a distance C O from a contact point T O to the center O is 1.5 to 3.0 [mm] inclusive, where the contact point T O represents a point where a vertical axis Y O , which passes through the center O and is perpendicular to the tube axis Z, intersects with the inner surface of the arc tube, the distance C O and a distance C M from a contact point T M to a midpoint M satisfy a relation C M /C O ≧0.8, where the midpoint M represents a midpoint between the center O and the contact point S, and the contact point T M represents a point where a vertical axis Y M , which passes through the midpoint M and is perpendicular to the tube axis Z, intersects with the inner surface of the arc tube, and a minimum thickness X [mm] of the arc tube in sealing part-side portions and a maximum outer diameter D [mm] of the light-emitting part satisfy a relation X/D≧0.2, the sealing part-side portions being portions of the light-emitting part that are close to the sealing parts.