Patent ID: 8030847

Claim:
A high intensity discharge lamp, comprising: a discharge vessel defining a discharge space being essentially free of mercury and containing at least a metal halide and a rare gas; two electrodes disposed within the discharge vessel for generating an arc discharge a wall forming the discharge space disposed between the electrodes, the wall having substantially circular cross-section with an inner diameter (d 1 ) and a wall thickness (w 1 ), and an outer bulb surrounding the discharge vessel and disposed at a distance (d 2 ) from a central position of an outer surface of the discharge vessel between the electrodes, the outer bulb being sealed and containing a gas filling having a predetermined thermal conductivity (λ) at 800° C., wherein the wall thickness (w 1 ) ranges from about 1.4 mm to about 2 mm, the distance (d 2 ) ranges from about 0.3 mm to about 0.8 mm, and a heat transition coefficient (λ/d 2 ) calculated as said thermal conductivity (λ) divided by said distance (d 2 ) ranges from about 10 W/(m 2 K) to about 100 W/(m 2 K).