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136
CINEMATOGRAPHIC ANNUAL
carbons at 145 amperes, the crater areas (Fig. 8) are 90 and 137 square millimeters and the intrinsic brilliancies (Fig. 9) are 737 and 620 candle power per square millimeter, respectively. It has been shown that for crater areas of 137 square millimeters the relative screen illumination with arc and lenses set properly is approximately 27 per cent more than for a crater area of 90 square millimeters with two sources of the same intrinsic brilliancy. After correcting for the difference in intrinsic brilliancy, it is found that only 7 per cent more light can be expected from the 16 millimeter carbons at 145 amperes than from the 13.6 millimeter -carbons at 120 amperes. Such calculations as these, which are made possible in part by the data given above, should be of some assistance in the more efficient use of this very fine source of light for projection of all kinds.
g
•u Z
§°
National High Intensity Carbons
INTRINSIC BRILLIANCY
! vs.
H CURRENT
90 100 re
CURRENT
Fig. 9. Intrinsic brilliancy vs. current.
150 -ec
In most commercial lamps the angle formed by the axis of the two carbons is fixed. It is well known, however, that the relative position of the two carbons along their respective axes appreciably affects the behavior of the high intensity arc. The following discussion will show that rather minor variations in position have an unexpectedly large effect on the amount of light and the steadiness of the arc.
The results of these variations are common to all types of high intensity lamps and carbons but most of the observations here discussed, unless otherwise specified, were made on 13.6 positives with Ys in. copper coated cored negative carbons at 120 amperes.