Why do passenger airplanes dim the cabin lights for take-off and landing? Gavin Haines reports.

Light-dimming is an in-flight mystery to many passengers.

My longheld and utterly wrong belief was that it was done to reduce light pollution around airports; you know, because nearby residents already had enough to grumble about without seeing the sky lit up every 20 seconds.

A poor explanation and one that serves only to remind us that I too am prone to dimness. In fact, the real reason that lights are turned low is for our safety in the event of an accident.

“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,” explains Patrick Smith, an airline pilot and author of Cockpit Confidential.

“The emergency path-lighting and signs will also be more visible. And it makes it easier to see outside, which helps you to maintain at least a basic sense of orientation - i.e. which way is up.”

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Raising your window shade during takeoff and landing is also part of the same strategy.

“It helps you remain oriented, and also makes it easier for the flight attendants to assess any exterior hazards, such as fire or debris, that might interfere with an evacuation,” says Smith.

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.

It’s also thought to be the reason why pirates wore eye patches; the theory being that by keeping one eye in darkness it would be better prepared when a pirate suddenly had to go into the pitch black bowels of the ship.

This would have given them a distinct advantage when they were ransacking another ship, which would have required them to fight on the deck and below.

Having an eye for light and an eye for night would also have allowed them to better defend their ship when it came under attack.

So now you know.

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Telegraph.co.uk