The Projection of Motion Pictures by Means of Incandescent Lamps

Abstract

In the development of a lamp suitable for the projection of motion pictures, it is essential that the light source be concentrated as closely as possible. After a number of experiments on filament arrangement, there have been developed two forms of filament for incandescent lamps for motion picture projection. The first successful arrangement of the filament was in two rows with coil sections parallel to each other, the coils in the second row of filament being placed so that they came between the coils in the first row. This arrangement gives the appearance of a solid source of light from a position directly in front. However, the condenser picks up light from all points within an angle of thirty to forty degrees from the line of projection. The edges of the condenser therefore pick up light from the front row, of coils and those portions of the coils in the back row which are not obscured by the coils in the front row. By means of the biplane arrangement, however, it is possible to obtain a greater amount of filament within the area which can be effectively used by the condenser; the useful area with practically any condenser system being not greater than ½ʺ square. If a spherical mirror is used back of the biplane coil, the reflected images make it possible to obtain a uniform screen.