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arrangement is different from the photoengraving field where a very common trim is a neutral enclosed arc upper carbon with a white flame positive lower. In this case the flame carbon must always be made positive because the flame chemicals travel through the arc stream from the positive crater to the negative crater. It is the flame materials that produce the light and wrong polarity or pure carbon open arc gives about one-sixth the photographic light of the v/hite flame arc. However, a positive flame upper carbon gives better efficiency with a flame negative lower as against a neutral negative lower.
On alternating current, both carbons should be flame carbons, as here the flame material feeds from both electrodes, and so this arrangement gives the maximum efficiency. The use of reactance ballast on alternating current lamps in place of resistance ballast increases greatly the efficiency of a white flame arc for equal power in the arc, and gives from 50 to 100% more light for equal power on the line. With reactance ballast on two or three flame arcs in series on no volts, the overall power factor is better than .85. Three flame arcs in series on no volts with metal coated carbons gave but very little if any more efficiency than two flame arcs in series.
We will now consider some of the typical flame lamps used in motion picture studios.
4. Rapid Developments of High Amperage Flame Lamps
4-a. description of several types of flame lamps
Special flame lamps have been developed to operate on A.C. or D.C. and in series on 220 volts or in multiple on no. This makes the lamp of universal use, and calls for no special attention to the electrical conditions. The resistance of the flame lamp to mechanical shocks, electrical shocks such as overvoltage and to bad weather conditions, has made it universally used for outside (of studio) motion picture work. Combined with all these advantages is the remarkable small weight of these lamps. For instance, some of the twin arc lamps weigh no more than 20 pounds for lights giving 8,000 or more horizontal candlepower, and with the light of a little greater actinicity than daylight. The amount of light is probably greater in proportion to weight than any other artificial light used in motion picture studios. Further improved design can greatly reduce this weight.
We will now show briefiy figures of a number of typical high amperage flame lamps. The following flame lamps are commonly used in motion picture work: Allison and Hadaway, Aristo, Bogue, Chicago Stage Lamp, Joyce, KHegHght, Macbeth, Scott, Simplex, SunHght, Universal, Wohl and others. As there is no article or book where these types have been shown collectively, I believe the following figures will be of interest.
The Aristo lamp. Fig. 7, is an enclosed arc lamp which has been much used by portrait photographers and in motion picture studios.
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