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1949
LEAD-SULFIDE PHOTOCONDUCTIVE CELLS
697
Curve C shows the variation of photosignal with light-source color temperature at constant total radiated power. It was obtained by dividing, point by point, the ordinates of curve A by the ordinates of curve B. These data indicate that the greatest transducer efficiency for the combination of a lead-sulfide cell and a silver sound track would be obtained with a light-source color temperature a little higher than
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TOTAL MOPILE PbS CE 3M2 TL PbS CE WATT
STEN LIGHT RCE RADIATION READINGS LL RESPONSE JNGSTEN LL RESPONSE
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2000° 2200° 2400° 2600° 2800° 3000° 3200° 3400° COLOR TEMPERATURE
Fig. 4 — Behavior of a lead-sulfide cell as a function of exciter-lamp color temperature; curve (£), plotted as a reference, gives the total radiation from a tungsten source per unit area. All curves are normalized to 2870 Kelvin.
2000 degrees Kelvin. This efficiency can only be realized, however, if exciter lamps are designed which will operate at this color temperature. Furthermore, since the energy flux through the scanning aperture varies with color temperature as shown by curve B in Fig. 4, the loss in power which would result from reducing the color temperature could only be recovered by utilizing a larger area of radiating surface. There is no good reason (except, perhaps, lamp life) for operating presently available exciter lamps at other than their rated voltage and