Читать книгу Motion Picture Operation, Stage Electrics and Illusions - Henry Charles Horstmann - Страница 20

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Current Required.—The measurement of the candle power of arc lamps has never been satisfactorily taken, and the difficulties encountered in determining it for a projecting arc are especially great because only a small part of the total light can be utilized and this is constantly varying. The light may, however, be assumed as proportional to the wattage of the arc, hence, we can best judge it by noting the volts and amperes. Where a very strong light is desirable, the arc is usually drawn out to some length; and as there is a rise in voltage, with a long arc, in such a case, the light increases at a greater rate than the amperage. In ordinary projection work, the arc is kept quite short because of the better definition obtainable by the use of such an arc; and we may assume that the light obtained is nearly directly proportional to the amperage. This relation of light and the current input to the lamp will be practically correct, especially if the size of the electrodes chosen is proportional to the amperage.