Patent ID: 7078860

Claim:
A metal vapor discharge lamp, comprising: (a) a translucent ceramic envelope, said ceramic envelope comprising a center bulb for defining a discharge space and side tubes being extended from both ends of said center bulb, said side tubes having outer diameters smaller than that of said center bulb, said center bulb and said side tubes being integrally molded; (b) a pair of current suppliers extending through hollows of said side tubes respectively, each of said current suppliers comprising an electrode and a lead-in wire, said electrode being fixed with a coil disposed in said discharge space, a first end of said electrode being disposed in said discharge space, a second end of said electrode being connected with said lead-in wire; (c) a sealant for hermetically sealing open ends of said side tubes to fix said lead-in wires to said side tubes; and (d) a light-emitting metal contained in said discharge space, wherein an inner wall of a seamless boundary portion between said center bulb and each of said side tubes has the smallest curvature radius of R i mm, an external wall of said boundary portion has the smallest curvature radius of R o mm, said center bulb has an inner diameter of D mm, said lamp has an electric power of P watts, and said curvature radius R i , said curvature radius R o , said diameter D and said electric power P satisfy: −0.00076 P +0.304 ≦R i /D ≦−0.00076 P +0.490, Formula (1) where P≦350 watts; and 1.28 R o ≦R i ≦1.39 R o . Formula (2)