Abstract
The paper describes the functions of a projector with particular reference to the light sources associated with it. It is shown that high brightness is usually the most important property of the source.
After a review of types of source at present used for projection, the possible advantages in the use of high brightness mercury vapour lamps are discussed and the characteristics of practical air-cooled lamps are described. Linear and compact source types are shown to be practicable, the latter having twenty or more times the brightness of the filament of a tungsten projector lamp.
Details are given of typical optical systems such as searchlights, and slide and film projectors, and the performance of the new lamps in them.
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