International projectionist (Oct 1931-Sept 1933)

Figures 1 through 3 illustrate the various types of carbon arcs now in common use. Fig. 4 shows the new A. C. projection arc. FIG. I FIG. m NEW A. C. CARBON ARC OFFERS H. I. LIGHT FIO. 3 WHILE the present low-intensity direct current projection arc in general Tise by the majority of smaller houses, when viewed by itself, apparently gives a brilliant white light, nevertheless this light when compared directly with that obtained from the high-intensity arc is yellowish-white in color. The object of extensive research by National Carbon Co. that has brought about the development of a new alternating current projection arc, has been to bridge the present wide gap in effective screen illumination that exists between the high-intensity arc used by the larger theatres and the present low-intensity direct current arc. By this new development the smaller theatre may have the advantage of a snow-white light for screen illumination similar to that enjoyed by , . ,. . the larger theatres and which is so '^^^.^ ^" ^''^'''^}^ ^^ere only alterdesirable for the satisfactory projec "^^^"^ ^"^^^"^ is available. eliminate entirely the use of motor generator sets, rectifiers, converters, as well as the power-consuming ballast resistances now required -with direct current projection equipment. This economy will appeal to all theatres lo tion of colored films. Not only has this marked improvement in color and brilliancy of light been accomplished by this new alternating current arc but it is also accompanied by other economical advantages. First, the power required to ■produce a given screen illumination 'with the new arc is less than that of -the low-intensity direct current arc. Desirable Characteristics The characteristics of this new alternating current arc are quite different from any other arc now in use. By means of special carbon design and control, it has been possible to effect an increase in arc current with a decreased arc voltage, thereby concentrating the light-giving power of the arc into a much smaller volume ■Secondly, with the new alternating near the carbon tips than has heretocurrent arc, it is possible, by the use fore been possible. This high concenof a specially designed transformer, tration of power in such a small space which is comparatively low in cost, to allows the light to be focused easily [10] by the means of a mirror, thereby making it a very desirable arc for projection. In reality, this new arc is a high-intensity alternating current arc. The color of light from this new arc is snow-white, and in operation it is very quiet and steady. Patent applications have been filed covering this new light system. The accompanying illustrations, Figures 1 to 3, are photographs of the various projection arcs now in common use. Figure 1 shows the direct current high-intensity arc. The characteristic tail flame is noticeable in this illustration. Figure 2 is a photograph of the direct current lowintensity arc, and Figure 3 shows the old type low-intensity, white flame, alternating current arc. Figure 4, which is an illustration of the new high-intensity alternating current arc, shows how radically different this new arc appears in contrast -with the older type arc and how the light-giving power has been concentrated in a small space between the carbons. It is evident from this photograph why this new arc is so admirably suited to mirror arc projection. A point of particular interest and one which is new to the projection field, is the use of the specially designed transformer as a source of