A minor mechanism of adaptation is the pupillary light reflex, adjusting the amount of light that reaches the retina. Changes in the sensitivity of rods and cones in the eye are the major contributors to dark adaptation.
Then, what is dark adaptation and why does it occur?
During light adaptation retinal sensitivity is lost. Dark adaptation is essentially the reverse of light adaptation. It occurs when going from a well light area to a dark area. Also, all the rod pigments have been bleached out due to the bright light and the rods are initially nonfunctional.
How long does it take for your eyes to adjust to the dark?
On an average it takes 30 to 45 minutes for your rods to be fully dark adapted to night vision. It also covers things such as Mesopic vision and Scotopic vision, eye health, and how to actually dark adapt. I suggest it as a good read. It's less than 14 pages.
How do your eyes adjust to light and darkness?
Preparing your eyes to see in the dark. 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.