# Dim the cabin lights for takeoff **URL:** \ **Category:** Factual Questions\ **Created:** [November 17, 2002, 1:34pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164 "2002-11-17T13:34:46Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![El\_Kabong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/el_kabong/32/496_2.png) [@El\_Kabong](https://boards.straightdope.com/u/El_Kabong)\ **Post date:** [November 17, 2002, 1:34pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/1 "2002-11-17T13:34:46Z")
Two aspects of commercial air travel I’ve never seen seen explained: 1. Why are the cabin lights dimmed for takeoff and landing? 2. Why must the window shades be up for takeoff and landing? I assume these are safety issues, but I’m not clear on the supposed benefits. ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [November 17, 2002, 3:12pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/2 "2002-11-17T15:12:50Z")
Dimming the lights reduces load on the aircraft electrical systems. The electricity for airplanes comes from generators which are turned by the engines. And the more current required takes power away from the engines that can be used for thrust instead of turning the power generator. On new 737’s for about the past year have switches in the flight deck that allow the pilot to shut down all unecessary equipment such as galley power, vacuum waste, and lighting such as reading and lavatory lights. Then of course, we have the jokers that think it is fun to shut off the switch while someone else is in the middle of a functional test job. I was told the last time I flew that the shades are opened to allow light into the cabin. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [November 17, 2002, 3:33pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/3 "2002-11-17T15:33:26Z")
I believe the window shades are open for safety reasons in the case of an emergency evacuation. There’s more light in the cabin and you can see what is outside in case it is a dangerous situation. As to whether this is an FAA regulation or something the airlines choose themselves I don’t know. ---
**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\ **Post date:** [November 17, 2002, 4:42pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/4 "2002-11-17T16:42:21Z")
I think the reason the lights are dimmed is that in the event of an emergancy and you have to leave the plane your eyes are adjusted to low light levels and so you can find your way out if the lights fail and it is dark outside. Also you would be able to see the floor-level emergency lights which are now fitted in planes. ---
**Author:** ![happyheathen](https://avatars.discourse-cdn.com/v4/letter/h/b5e925/32.png) [@happyheathen](https://boards.straightdope.com/u/happyheathen)\ **Post date:** [November 17, 2002, 7:29pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/5 "2002-11-17T19:29:07Z")
Why are the cabin lights bright while on the ground? GPU - Ground Power Unit - a separate generator which supplies power while the propulsion engines are off - it is turned off when the propulsion engines are started, putting the load on the p. engines, which really do have better things to do during take-off. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [November 17, 2002, 11:45pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/6 "2002-11-17T23:45:47Z")
Did you mean APU - Auxillary Power Unit? The APU is a small turbine in the aircraft, a GPU is a power cart separate from the aircraft. The p. engines have better things to do during takeoff, but prior to takeoff they have nothing much to do and are happy supplying power so that the passengers can read the emergency cards (as we all do), and books, and things. ---
**Author:** ![happyheathen](https://avatars.discourse-cdn.com/v4/letter/h/b5e925/32.png) [@happyheathen](https://boards.straightdope.com/u/happyheathen)\ **Post date:** [November 18, 2002, 12:32am UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/7 "2002-11-18T00:32:50Z")
oops, yeah… one of them pu’s… ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [November 18, 2002, 2:14am UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/8 "2002-11-18T02:14:57Z")
I was told that the shades had to be up so that the cabin crew could if necessary make a visual check and report to the flight crew in case of a wing/engine problem which could not be diagnosed from the flight deck. ---
**Author:** ![Daniel](https://avatars.discourse-cdn.com/v4/letter/d/3ec8ea/32.png) [@Daniel](https://boards.straightdope.com/u/Daniel)\ **Post date:** [November 18, 2002, 4:12am UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/9 "2002-11-18T04:12:37Z")
I always assumed the windows, like the seat positions and trays, were just something we do so the staff doesn’t have to go to every seat and readjust everything for the next group of passengers. Basically, “put it back the way you found it.” ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [November 19, 2002, 6:14pm UTC](https://boards.straightdope.com/t/dim-the-cabin-lights-for-takeoff/137164/10 "2002-11-19T18:14:37Z")
During _takeoff_, **Daniel**?