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XENON
Projection Lamps
PART 2 CARE AND OPERATION
By ROBERT A. MITCHELL
As explained in the first installment of this article, the high-intensity carbon arc reigns supreme for the projection of motion pictures on large screens. It has the highest intrinsic brilliance of any man-made illuminant, and is optically the most efficient because of its concentrated radiating area. Nevertheless, the xenon short-arc bulb is a very attractive substitute for the smaller "simplified" highintensity carbon arc, and it has unique advantages which have already proved valuable in theatre use.
The outstanding advantages of xenon lamps are pushbutton ease of operation (no arc to "strike," no trimming of the lamp with carbons, no optical variations, no dirty ash to soil the lamphouse), an unvarying daylight-white color of the light, a continuous, equal-energy type of spectrum ideal for the projection of color films, a constant
Familiarity with the operating characteristics of the new xenon projection lamp may soon prove to be a valuable part of the projectionist's armamentarium of technical knowledge. This, the concluding installment of a two-part article, sets forth the basic principles and "do's and don't's" of xenon lamp operation.
The carbon arc is still the undisputed monarch of motion-picture projection on screens having a width of 28 feet and more (85% matte surface), but the convenient and easy-to-operate xenon lamp has amply demonstrated its value on matte screens up to 27 feet wide (and on wider directional screens) in many European theatres and American preview rooms.
The incipient new wave of prosperity in the motion-picture industry bids fair to sweep the revolutionary new xenon lamp into thousands of American theatres where the unavoidable screenlight discolorations and variable output of the smaller "simplified" HI arc lamps are rightly considered incompatible with the high pictorial quality of modern black-and-white and color prints. So herewith a practical introduction to xenon!
ANODE
CATHODE
FIG 1 — Anatomy of the xenon gas-discharge bulb. Note that the anode (positive electrode) is positioned above the cathode (negative electrode) when the bulb is installed in the lamphouse.
color temperature regardless of electrical load, no troublesome moving parts, absolute cleanliness, and an overall operating cost the same or less than that of simplified HI carbon arcs of equivalent luminous output.
Output's of Xenon and Carbon Arcs
It was stated in Part I that xenon lamps are suitable for use only in those theatres where carbon-arc lamps burning no more than about 55 amps, are powerful enough to provide a screen brightness of not less than the standard minimum of 10 footlamberts with the projector shutter running. Exact light values are given in the accompanying two tables.
Table 1 lists the maximum widths of two common types of screen for 10 footlamberts (with the shutter) when simplified HI arc lamps burning up to 60 amps, are used. In conformity with the customary way of rating
International Projectionist July, 1963