Some studies of 1941–1942 indicated that adaptation under red light was faster than in darkness. A recent (May 26, 1952) research report originating from the Naval Air Station at Pensacola seems to show a facilitative effect of red light on dark adaptation and has renewed interest in this problem. Some of the earlier data purporting to show this effect, additional material previously unpublished, and also new studies made at Yale by the method of simultaneous differential monocular adaptation are here presented and discussed. Adaptation goggles were used for 25 min under illumination of 8 mL. The filter over one eye was a glass disk made of Corning No. 2403, deep red, 3.5 percent photopic transmission, over the other eye an opaque cardboard disk which excluded all light. Dark-adaptation thresholds (Hecht-Schlaer adaptometer) violet light (Corning 5513), measured alternately on the two eyes showed for 16 college student subjects lower values, i.e., increased light sensitiveness for the eyes adapted in darkness. In the period 6 min after removing the goggles the mean threshold difference between results for red and opaque procedures in the first test was −0.153 log μμL, <P=0.01; in the second test with the goggles reversed on the two eyes the mean difference favoring the opaque side was −0.182 log I, μμL, <P=0.01. The earlier and later results are not easily harmonized. The author argues in favor of the monocular method as an appropriate one for the study of this problem.
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