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ffSuprex" Type High Intensity Arc
The most satisfactory source of power is a constant voltage source near enough to the arc voltage to permit the use of a small ballast resistance or a source with a falling volt-ampere characteristic and a no-load voltage not greatly in excess of the arc voltage. Several different types of units are now on the market which have characteristics suitable for these non-rotating, high-intensity, D.C. arcs. Each has its own peculiar advantages but all are characterized by a comparatively large increase of current with a decrease in arc voltage.
With a suitable source of power and proper adjustment of the control mechanism for the conditions under which the arc is operated, these new Suprex type, D.C, high-intensity arcs supply to the smaller theatres all the advantages of light quality and intensity which the higher amperage high-intensity lamps have given the larger theatres. They produce 100 to 200 per cent higher levels of screen illumination than is available from the low-intensity D.C. mirror arc and at a lower operating cost per unit of light volume.
These later type high intensity arcs, the A.C. high intensity arc and the Suprex type D.C. arc, give best projection within a relatively narrow range of arc position. This requires a control mechanism adapted to maintaining the position of the arc within these limits and, in the case of the Suprex type lamps, providing a fairly wide range of positive-to-negative feed ratio. This result is very effectively accomplished by most of the lamps now on the market so that the projectionist, with reasonable attention, should encounter no difficulty in maintaining proper operating conditions at the arc.
In the design of the new lamps, both A.C. and D.C, advantage has been taken of the fact that the brilliant gas ball from which the light emanates projects somewhat beyond the lip of the crater. As a result, the light at 90 degrees, that is, at right angles
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