During dark adaptation, which photopigments regenerate first?

During dark adaptation, the photopigments that regenerate first are the cone photopigments. This process occurs when there is a shift from bright light conditions, which predominantly stimulate cones, to low light conditions where rods become more prominent due to their higher sensitivity in dim lighting.

Cones, which contain photopigments such as photopsins, regenerate relatively quickly compared to rod photopigments like rhodopsin, which takes longer to regenerate fully in the dark. This is because cones are designed for high illumination levels and adapt rapidly to changes in light.

In contrast, rods adapt more slowly due to their need to recover from bleaching that occurs under bright lighting conditions. Additionally, the regeneration process of photopigments in rods involves more complex biochemical pathways, contributing to the delayed response during dark adaptation.

Thus, in scenarios transitioning from light to dark, it is the cone photopigments that are the first to regenerate, allowing for a quicker adaptation to lower light levels.