Very little is known about the function of rod cells at illumination levels exceeding the cone threshold. The cones, presumably with a higher level of awareness, dominate the picture at high i n t e n s i t i e s. Although both cone and rod cells cease to function when the intensity level is reduced below their respective thresholds, it cannot be said that the rod cells cease to function when the intensity is raised from scotopic levels to photopic levels above the cone threshold. In the course of dark adaptation one cannot plot rod adaptation during the first several minutes because during this time the cones have a greater sensitivity to light and take over the function of light perception. It is only when the sensitivity of the retina has recovered sufficiently so that intensities below the cone threshold can be recorded that the rod curve makes
MANDELBAUM J, NELSON E. Rod Activity at Photopic Intensities. AMA Arch Ophthalmol. 1960;63(3):402–408. doi:10.1001/archopht.1960.00950020404002
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