A visibility curve depending on about 15 observers has been taken at an intensity comparable to the lowest used in darkroom work. A series of determinations of the wave-length of maximum visibility for several intensities and observers has also been made giving a curve extending from near the dark adapted threshold to about 2 foot lamberts. The observations were all made with the natural pupils and binocular vision. Comparisons with some previous work of other authors are made. The wave-length of maximum visibility at the highest intensity corresponds very closely with that of the standard I.E.S. photopic curve. At the lower levels, values are found approximating those given by König in his complete curve, and by Hecht for an intensity 2.7 times the dark adapted threshold.
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