Why airplane lights are dimmed during takeoff and landing
One of the mysteries of flying that many passengers have pondered is: why does the flight crew dim the plane’s cabin lights for takeoff and landing?
The reason is safety.
Dimming the lights allows your eyes to pre-adjust to darkness, so that you're not suddenly blinded if something happens and the power goes out, and you're dashing for the doors in darkness or smoke. It also makes the emergency path-lighting and signs more visible and makes it easier to see outside, which helps you to maintain your sense of orientation.
The obligatory raising of your window shade during takeoff and landing is also part of the same strategy.
The human eye can take up to 10 minutes to fully adapt to darkness, which is valuable time if you need to evacuate an aircraft in a hurry.
Fun fact: This is also thought to be the reason why pirates wore eye patches, even if they had two functional eyes. Keeping one eye in darkness would be a good preparation when the pirate suddenly had to go into the pitch black bowels of a ship to fight.
This would have given them a distinct advantage when they were ransacking another ship, or defending their own ship when it came under attack.