| 摘要 |
In a metal halide arc discharge lamp having a light emitting arc discharge tube surrounded by a heat absorbing, light transmissive shroud hermetically sealed within an outer lamp envelope, more nearly isothermal operation of the arc tube surface is achieved by using a shroud having a geometry (e.g., a hollow frustum of a cone) such that the shroud is closer to the cooler portions of the arc tube than to the hotter portions. At steady state lamp operation, the shroud absorbs heat emitted by the arc tube and radiates a portion of the absorbed heat back to the arc tube. By having a shroud geometry and spacing such that the inner surface of the shroud is closest to the coolest portions of the arc tube and furthest away from the hottest portions of the arc tube, the shroud radiates more heat back to the cooler portions, thereby providing more nearly isothermal operation of the surface of the arc tube than can be accomplished with a coaxial, cylindrical shroud or no shroud.
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