Dark-adaptation luminance thresholds for the resolution of detail following different durations of light adaptation.

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Abstract
Dark adaptation curves representing 3 levels of visual acuity were determined following preadaptation to a 1000 ml field for durations from 1 sec. to 10 min. At all acuity levels, the initial thresholds for an acuity grating rise, and the speed of dark adaptation decreases as duration of preadapting light increases from 1 sec. to approximately 5 min. These effects are less pronounced at the highest acuity investigated, 0.62. A threshold response at this level represents cone adaptation exclusively. At lower acuities, 0.083 and 0.042, an additional effect occurs as a function of duration. The shorter the period of light adaptation, the less prominent is the primary cone dark adaptation, and the sooner does the rod dark adaptation appear. Duration of light adaptation, in addition, has a marked effect upon the level of threshold luminance early in the course of dark adaptation. The effect becomes progressively reduced as time in the dark increases. Finally, as the level of acuity increases, the threshold luminance also increases, depending upon the amount of change in acuity and the preadapting duration.