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130
CINEMATOGRAPHIC ANNUAL
TABLE III.
S. R. A. Positive Carbons Angular Light Distribution 12 Millimeter Carbon at 30 Amperes
Cumulative
Lumens Light
Pe
r Cent
Per Cent
Flux in
of
Total
of Total
Angle
Av. Cp.
Various Zones
L
umens
Lumens
0-10
8695
825
3
3
10-20
8360
2360
9
12
20-30
7590
3520
13
25
30-40
6670
4180
16
41
40-50
5730
4430
17
58
50-60
4730
4230
16
74
60-70
3600
3570
14
88
70-80
2220
2260
9
97
80-90
720
780
3
100
26,155 (Total Lumens) 14 Millimeter Carbon at 47 Amperes
Cumulative
Lumens Light
Per Cent
Per Cent
Flux in
of Total
of Total
Angle
Av. Cp.
Various Zones
Lumens
Lumens
0-10
13,950
1320
3
3
10-20
13,100
3700
9
12
20-30
12,200
5600
14
26
30-40
11.350
7130
17
43
40-50
9650
7460
18
61
50-60
7630
6850
16
11
60-70
5340
5300 .
13
90
70-80
2930
3100
7
97
80-90
1015
1110
3
100
41,5 70 (Total Lumens)
The optical systems commonly employed in the present low intensity reflecting arc lamps use a parabolic reflector with a condensing lens or an elliptical reflector alone. Irrespective of the system used, the light pick-up from the arc has usually been a cone of 120 degree opening which, according to Table III. would include approximately 75 per cent of the light from the positive crater. The light gathered by the reflector is focused on the aperture plate in the form (neglecting spherical aberration) of an image of the crater. The magnification of the system is approximately 6 to 1. Under these conditions it is theoretically correct that the optical system is saturated when a current of 21 amperes is used on the proper size carbon and the higher currents merely give more light to be absorbed or reflected from the aperture plate. It can be seen that this is plausible by a reconsideration of Fig. 1. In this figure, instead of projecting the crater face onto the aperture plate, the width of the aperture plate opening with the proper reduction for 6 to 1 magnification has been projected back onto the crater. The values of intrinsic brilliancy for the portions of the craters within the aperture plate width indicate that no more light could be expected to go through the aperture plate from a 13 mm. carbon at 44 amperes than from a