Abstract
We discuss the factors in the design of an economical incandescent light source using a filter envelope which directs heat back to the filament but allows light to be transmitted. Achievement of the necessary performance requires a new concept in the design of the lamp and a high-performance coating. The use of reactive sputtering to prepare dielectric-silver-dielectric filters into pressed glass semi-ellipses gives a 60% increase in luminous efficiency as compared with a standard unit.
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