In daylight, rods are known to be bleached: we have to wait some time after going into darkness before scotopic vision becomes effective. But, as I understand, peripheral vision is also mostly due to rods, since away from the fovea, cone density rapidly declines.

But I wonder then: if rods normally saturate in bright light, why does peripheral vision still work in daylight?


Short answer
In photopic lighting, peripheral vision is mediated by cones.

The rods are indeed saturated at daylight, and even at twilight (source: Nature). However, the cones are active and although their density in the periphery is low, they are still present (Fig. 1). Hence, peripheral vision in photopic lighting conditions is mediated by cones. Because of their low density in the periphery, however, visual acuity is low (Kolb, 2012).

Fig. 1. Rod & cone densities in the retina. (Kolb, 2012)

- Kolb, Photoreceptors, In: Webvision: The Organization of the Retina and Visual System. Utah University

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    $\begingroup$ This seems to contradict this answer, which doesn't appear to rely on scotopic vision to explain its point. Is it wrong? $\endgroup$ – Ruslan Oct 23 '18 at 22:00
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    $\begingroup$ @Ruslan For primates, AliceD's answer here is better. See also Stabell, U., & Stabell, B. (1976). Absence of rod activity from peripheral vision. Vision research, 16(12), 1433-1437. and Stabell, U., & Stabell, B. (1982). Color vision in the peripheral retina under photopic conditions. Vision research, 22(7), 839-844. $\endgroup$ – Bryan Krause Oct 23 '18 at 22:54

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