Which photoreceptors bleach faster under typical light exposure?

• A. Cones
• B. Rods
• C. Both equally
• D. None

Answer: (B)

When light activates photopigments, they change chemically and become bleached. The pigment in rods, rhodopsin, is incredibly light-sensitive, so a typical amount of ambient light quickly converts a large portion of it to the bleached form. That rapid bleaching means the rod system loses its ability to respond until the pigment regenerates in darkness. Cones have different pigments and are built to operate in brighter light; these cone pigments are not bleached as quickly under the same exposure and can be restored more readily, so they maintain function while rods are temporarily washed out. So, under ordinary light levels, the rod photopigment bleaches faster than the cone pigments, leading to the rod system saturating earlier in bright conditions.