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490 FREDERICK E. BARSTOW November
illumination essentially invisible to the pilot, C. W. Wyckoff of the Edgerton, Germeshausen & Grier staff undertook to re-evaluate the relative merits of working in the ultraviolet or infrared regions of the spectrum. It was determined that although the over-all efficiency in the ultraviolet region was considerably greater than that in the infrared, it would have been necessary for the pilot to wear light yellow glasses to cut out the blue portion of the spectrum. In addition to this disadvantage, the contrast using ultraviolet light was considerably less than that obtained with infrared light. Further, the ultraviolet light would cause the luminescent dial paints to glow,
Fig. 5. Quartz flashtube for infrared recorder compared in size to a 35-mm film cartridge.
which might or might not have been a disadvantage. Having concluded that an infrared source had the greater advantage, the CAA outlined certain requirements for the recorder : (1) area to be covered, 11 X 14 in.; (2) camera to instrument panel distance, 36 in.; (3) maximum aperture, //1. 9; (4) picture rate, one per second; (5) power source, 12-v battery; and (6) minimum size and weight.
A few simple photographic tests with standard flashtubes indicated that a special flashtube would be desirable. Two seemingly incompatible factors enter into the design of a flashtube which is to be operated at high repetitive rates. If it is small, it will overheat due to the average power input, but will have high efficiency. If it is