It's much faster for our eyes to adapt to bright light than to
adjust for the darkness. Cones attain maximum sensitivity in five
to seven minutes while rods require thirty to forty-five minutes or
more of absolute darkness to attain 80% dark adaptation.
Both cones and rods participate in dark adaptation, slowly
increasing their sensitivity to light in a dim environment. Cones
adapt faster, so the first few minutes of adaptation reflect
cone-mediated vision. Rods work slower, but since they can perform
at much lower levels of illumination, they take over after the
initial cone-mediated adaptation period.