(57) A metal halide lamp having a relatively high anticipated life and particularly suitable
for architectural lighting is disclosed. The metal halide lamp has a double-ended
arc tube serving as its light source. The arc tube has a halogen gas formed from vaporized
metal halides along with a mercury vapor. The amount of mercury contained in the arc
tube is selected to effectively establish an A.C. operating voltage in the range of
about 100 volts to about 150 volts. The metal halide develops a vapor during the operation
of the arc tube. The halide is selected from the group of metals consisting of sodium,
scandium, thorium, and mixtures thereof. The halide is further selectable as a compound
cadmium iodide. Further disclosed are various embodiments of illuminating lighting
systems that provide beam patterns particularly suitable for illuminating a limestone
building.
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