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Report on the New Concentrated-Arc Lamp
Many Possibilities Seen for the New Arc That Approximates Point-Source of Light
During the war a new type of light source was developed under a contract issued through the Optics Division of the National Defense Research Committee. The new lamp, called the concentrated-are lamp, is basically a directcurrent are lamp made with permanent, fixed electrodes which are sealed into a glass bulb filled with an inert gas. The name, “concentrated-arc,” comes from a characteristic of the lamp which makes it possible to concentrate the arc activity upon a small portion of the electrode so as to produce a very high intensity light source in the form of a luminous circular spot which is fixed in position, sharply defined and uniformly brilliant.
The degree to which this concentration may be carried is illustrated by the 2-watt concentrated-are lamp whose luminous spot is only 0.003 of an inch in diameter with a maximum brightness of 100 candles per sq. mm. Ordinary tung
FIGURE 1—A line of standard-size concentrated-arc lamps has been developed in sizes from 2 to 100 watts. Larger lamps are made, but the designs have not been standardized. The lamp is basically a direct-current arc lamp, made with permanent, fixed electrodes which are sealed into a glass bulb filled with an inert gas.
W. D. BuckincHAM and C. R. DEIBERT Engineering Department of the Electronics Division, The Western Union Telegraph Company
sten filament lamps operate at about 10 candles per square millimeter while the brightness of the crater of a carbon arc lamp is about 135 candles per square millimeter. The area of the spot formed increases with the current so that a 100watt lamp has a spot 0.059 of an inch in
This article originally appeared
in the May, 1946, issue of the Journal of the Optical Society of America. Permission to reprint has been granted by the Western Union Telegraph Company and Dr. George R. Harrison, editor of the Journal,
yas
1946-47 THEATRE CATALOG
diameter, while the spot of a 1500-watt lamp is 0.35 inch in diameter.
The source of the light is an incandescent spot which forms on the specially prepared negative electrode or cathode. This cathode is the unique element of the new lamp. It is made by packing zirconium oxide into a small cup or the open end of a tube which is made of tungsten, molybdenum, or tantalum, these metals being selected because of their high melting temperatures.
The positive electrode or anode, also made of a metal with a high melting point, consists of a simple sheet or plate which has sufficient radiating surface so that during operation it will reach no more than a dull red heat.
These two electrodes are mounted in the bulb so that the exposed oxide surface of the cathode is but a few hundredths of an inch from and directly behind a hole in the center of the anode.
The name, ‘‘concentrated-arc,’” comes from a characteristic of the lamp which makes it possible to concentrate the arc activity upon a small portion of the electrode, so as to produce a very high intensity light source in the form of a luminous circular spot in a fixed position, sharply defined, and uniformly brilliant,
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