Journal of the Society of Motion Picture Engineers (1930-1949)

Record Details:

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358 J. L. McCoy tJ. $. M. P. £. with a shield. A window is cut in one side to admit the light to be measured. The photo-electric cell unit is connected to the meter by a six foot double conductor cord making it possible to move the cell unit around within that radius without moving the case. The instrument contains a commercial, portable microammeter calibrated directly in foot-candles. The smallest size "B" batteries are wired and mounted in the case. As very little energy is required, the .battery life will be about its shelf life. The photo-electric cell is generally known as a light-sensitive tube having somewhat the appearance of a radio tube. The tube has two distinct parts, an anode and cathode. The cathode is coated, lightsensitive material giving the tube its characteristics. The resistance of the cell will vary with the intensity of the light which strikes it. Many other commercial uses have been found for the photo-cell. It is used as a smoke detector to sound an alarm in case of fire or to count the product of quantity production as the cars are counted as they pass through the Holland Tunnel by the interrupted beam of light. The cell plays an important role in several different schemes of motion picture sound reproduction. There are a number of different types of cells and their characteristics vary materially with the elements used. They can be made of different materials to respond to different wave-lengths of light. Dr. Rentschler of our research department has constructed a photo-electric cell that will respond only to the ultra-violet region of the spectrum. This cell is now being used in an ultra-violet recording device, making it possible to obtain a quantitative reading in ultra-violet units. The cell used in our light intensity meter is a special cell having a very broad response, covering the visible spectrum. This response is such that it will fit in very well for light measurements where the combination of Mazda light and panchromatic film is used. A spectroscopic study of the response of the panchromatic film when plotted against the light of the Mazda lamp shows that the results are somewhat near a straight line, making it possible for the meter to give an integration that will come close to the photographic results obtained with given light values. The use of this meter is suggested to be of considerable value when colored pictures are taken because of the integration of the values of different wave-lengths of light through the visible spectrum. The same cell can also be used for the measurement of north sky daylight, giving approximately the same values for the same intensity from a photographic standpoint. The photo-cell