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A 13.6-MM. SUPER-HIGH-INTENSITY CARBON FOR PROJECTION*
D. B. JOY**
Summary. — A new 13.6-mm. super-high-intensity carbon is described which will burn at currents as high as 190 amperes and which has a higher intrinsic brilliancy and a more uniform distribution of light across the crater face than the regular 13.6-mm. carbon rated at 120 to 130 amperes.
Tests comparing the light projected upon a projection screen by this new carbon and by the regular carbon show conclusively that the available light has been increased by at least 30 per cent. The arc lamp used with the carbons must be properly designed to take care of the increased current and carbon consumption.
The regular 13.6-mm. high-intensity positive carbon burning at 120 to 130 amperes and used in the condenser type of high-intensity lamp has been the light-source used in the largest theaters of the country for a number of years. The increase in general theater lighting, the size of the picture, the size of the theater, and the anticipated use of color have caused demands from a number of theaters for a 13.6-mm. high-intensity carbon that will furnish more light than is available from this standard carbon.
In addition to this, in the last few years, background projection for process photography has been used extensively in motion picture studios. This process, which has been described by Popovici,1 Harrison,2 and others consists in projecting a picture of the desired background through a translucent screen and rephotographing this picture with foreground objects to give the final composite scene. Because of the light loss "occurring through the screen a very large amount of light is desired. It is also essential that the light-source have a considerable range of intensity because of the difference in density of the films being projected. A further requirement is that there should be a minimum decrease of light at the sides of the picture.
It is therefore evident that both from the standpoint of projecting
* Presented at the Spring, 1936, Meeting at Chicago, 111. ** Laboratory, National Carbon Co., Inc., Fostoria, Ohio.
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