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Sept., 1936J A 13.6-MM. SuPER-HlGH-lNTENSITY CARBON
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in order to avoid any difference3 in light or light distribution caused by a change in either the position of the carbons or the arc flames. The light upon the projection screen was measured by means of Weston photronic cells corrected by means of a green screen to approximate the sensitivity of the eye. These cells were placed at the positions shown in Fig. 3c. The cells at the sides and corners were placed at the edges of the light zone; and their readings, compared with the reading of the center cell, give a true picture of the decrease in the light from the center to the sides or corners of the screen.
Preliminary measurements showed that the super-carbons give an increase in light when the positive carbon is held at exactly the same position with respect to the optical system, and also tend to
FIG. 3. (a) Optical system used in tests; (b) positions of carbons and arc; (c) location of phototronic cells on projection screen.
build up the light at the sides of the screen. This, of course, would be anticipated from the shape of the intrinsic brilliancy curves. In order to place the measurements upon a common basis, it was decided to take a series of readings of the screen light, moving the lenses with respect to the aperture plate and carbons. By this method the distribution of light falling upon the projection screen could be varied over a considerable range, and the light from the two types of carbon could be compared directly for the same light distribution. Screen light measurements were made of the regular carbon at 120 and 130 amperes and of the super-carbon at 160 and 180 amperes. These measurements were all grouped according to the light distribution upon the screen and were then plotted as shown in Fig. 4. In this figure the total lumens projected to the screen are plotted