US Patent 7911144 Metal halide lamp and vehicle headlamp

The invention relates to a metal halide lamp for a vehicle headlamp comprising a cylindrically-shaped discharge vessel (23) having a ceramic wall which encloses a discharge space comprising Xe and ionizable filling, and a cylindrically-shaped outer bulb (21) surrounding the discharge vessel (23). According to the invention a portion (25, 26) of the surface of the outer bulb (21) facing away from the discharge vessel (23) is shaped as a negative lens. Preferably, the portion (25, 26) encompasses a segment of the outer bulb (21) with a segment angle α in the range between 30≦α≦60°. Preferably, the portion (25) forming the negative lens is shaped as a flat surface.