Which type of photoreceptors is more sensitive during the initial phase of a dark adaptation curve?

During the initial phase of dark adaptation, rod photoreceptors are more sensitive than cone photoreceptors. Rods, which are responsible for vision in low-light conditions, reach their maximum sensitivity more quickly than cones do when transitioning from light to darkness. Cones operate best in well-lit environments and take longer to adapt as they are more specialized for daytime and color vision.

In darkness, rods increase their sensitivity to low light levels through a process of visual pigment regeneration, allowing them to eventually enable night vision. This is a key aspect of how our eyes adjust when moving from a bright environment to a darker one. Initially, the cones may still be somewhat active, but their ability to detect light diminishes considerably compared to the enhanced performance of rods as adaptation progresses. Thus, the correct choice reflects the understanding of the biological mechanisms underlying dark adaptation in human vision.