Richardson's handbook of projection (1927)

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784 HANDBOOK OK PROJECTION FOR Various Types of Light Source THERE are now in use (1927) four available light sources for motion picture projection. Each of these sources differs widely from the other in the matter of efficiency of results obtained per watt of electric energy expended, each producing a distinctly different result in the items of screen illumination and light tone, and each demanding expert adjustment and handling in order to produce maximum results — especially maximum results at a minimum consumption of electric power and expense for replacement of apparatus, or parts thereof. These various light sources are (a) the ordinary electric arc (b) the high intensity arc, (c) the reflector arc lamp and (d) the incandescent, the latter commonly, though erroneously dubbed the "Mazda." Each of these light sources, except perhaps the first named, which is the oldest of them all, has an appropriate place in theatrical motion picture projection, the particular one best suited for use in any particular installation being entirely dependent upon (a) local conditions and (b) the individual ideas of the management as to what combination of screen brilliancy and light tone is most pleasing and satisfactory. Broadly, the high intensity produces a very bright screen and a harsh light tone. It consumes a maximum amount of electric power and carbons. It is a very hot light source, hence is very hard on collector condenser lenses, and on certain of its own parts. Put in another way, it is expensive in operation, but gives a maximum screen illumination — the brightest that can be had with any present known light source. The ordinary arc is relatively expensive in operation. It consumes much carbon and electric power for the intensity of