Abstract A high pressure metal halide discharge lamp containing mercury and metal halides including an alkali metal halide and wherein the segregation of alkali metal (sodium) is minimized. In a lamp for vertical operation, the normally asymmetric alkali metal distribution in the vapor phase is offset or reduced by an asymmetric lamp construction using at the lower end one or more of a smaller electrode which runs hotter, a heat-reflecting coating, or a tapered end chamber. This construction drives the condensed metal halides away from the lower end while raising the temperature of the excess halide, and exerts a net force on the alkali metal atoms in the vapor phase to drive them toward the upper end of the lamp. The result is that segregation of the alkali metal is reduced, leading to higher efficiency, improved color and reduced color separation.
A lamp as in claim 1 wherein said asymmetric construction resides in at least one of the following features: a smaller electrode at the lower end than at the upper end, a more extensive heat reflective coating on the lower end, and a tube end configuration reducing heat loss at the lower end.
Claim 2
Dependent Claim
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A lamp as in claim 1 wherein a heat reflective coating is applied to the lower end only and extends beyond the tip of the lower electrode.
Claim 3
Dependent Claim
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A lamp as in claim 1 wherein the alkali metal halide is sodium iodide.
Claim 4
Dependent Claim
30 words
A lamp as in claim 1 wherein the alkali metal halide is sodium iodide and a heat reflective coating is applied to the lower end only of the arc tube.
Claim 5
Dependent Claim
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A lamp as in claim 5 wherein the heat reflective coating extends beyond the upper end of the lower electrode.
Claim 6
Dependent Claim
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A lamp as in claim 6 wherein the filling of metal halide includes thallium and indium.
Claim 7
Dependent Claim
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A lamp as in claim 1 wherein the alkali metal halide is sodium iodide, a smaller size of electrode is provided at the lower end than at the upper end, and a heat reflective coating is applied to the lower end only of the arc tube.
Claim 8
Dependent Claim
59 words
A lamp as in claim 1 wherein the alkali metal halide is sodium iodide, a smaller size of electride is provided at the lower end than at the upper end, a heat reflective coating is applied to the lower end only of the arc tube, and a tube end configuration reducing heat loss is provided at the lower end.
Claim 9
Dependent Claim
16 words
A lamp as in claim 9 wherein the filling of metal halide includes thallium and indium.