Why can't you see right away when the lights go out?

Walk into a dark room and you are nearly blind, then 25 minutes later you can read shapes you could not see at all.

In darkness your rod cells slowly rebuild a pigment called rhodopsin that bright light had bleached. The first few minutes give little, then rods take over and most of your night vision arrives by 20 to 30 minutes, with sensitivity still creeping up toward its peak near 40 minutes.

During a power cut you fumble for your phone at first, but if you just sit still for half an hour the room slowly fills with visible furniture.

Your eyes keep getting better in the dark for half an hour or more, far past the moment they feel adjusted.

Before night driving or stargazing, give your eyes time in the dark first, and avoid bright screens that bleach the pigment all over again.

Rods recharge like a slow battery: a quick start, then 20-30 minutes to mostly full.

Learn the idea and practice English at the same time.