TIWLTL (today I would like to learn) why on landing and take off in the dark, the internal lights on a plane are dimmed.
I have heard a few reasons in pubs around rev world including minimum loads on generators and therefore maximum available for engines, or higher brightness is too much and the plane is too bright for controllers (affects night vision etc.
@The Dreamer - could you shed some light on this (pun intended
?)
It's simply to adjust your eyes to a darker environment in case of an emergency requiring evacuation.
In the event of an emergency requiring an evacuation, the aircraft will lose all electrical power as the engines, including the APU (Auxiliary Power Unit) are shutdown, and the cabin will be plunged into darkness, with just the emergency lighting available to guide you to the exits.
A rapid change from a bright environment to a very dark one, will a. be much harder to see in, and b. likely to engender even more panic from anyone in the least bit nervous about what's going on (as most probably will be).
The amount of power consumed by the lights is a fraction of other systems on board, and isn't a consideration from a performance perspective.
For your pub mates...
On some types of aircraft, the pressurisation system is switched off for the take-off run to allow the engines to generate more power, as on most jet aircraft the cabin air is pressurised using air 'bled' from the engines, which reduces their efficiency slightly.
This might be done for two reasons, one for when you are performance limited on shorter/hotter/higher runways, where you want the absolute maximum amount of power available. And at other times, by allowing the engines to 'potentially' give you more power, you can actually then 'de-rate' the take-off power by a greater percentage, and actually reduce wear and tear on the engines.
Almost every take-off we do involves 'reduced thrust', so reducing wear and tear, and also making the chance of an engine failure during that critical phase less likely - so we win all-round. The car analogy would be the difference between accelerating gently up to motorway speeds, and planting your foot hard on the accelerator.
It is why, in
broad terms, if you watch airliners take off, all of the twin engine aircraft will rotate at
roughly the same spot on the runway, no matter how heavy or light they are. The heavier ones will be using more thrust, and the lighter ones will have reduced their take-off thrust - so they all end up at roughly the same spot.
(Note, not applicable on very long runways such as Heathrow, as there is only so much 'thrust reduction' we can do, so very light aircraft will inevitably have reached this, and still get airborne quicker than a much heavier aircraft).
There are other variations; aircraft with more engines will use more runway to get airborne, and there are variations in stopping distances etc. But generally, the idea is to reduce power to the point where the runway just about becomes performance limiting, i.e. you apply just enough power to reach the required speeds at the appropriate point on the runway, and no more (there are margins built in).
So, there you go. Probably a bit more info than you needed, and it's a very basic generalisation - but you'll be able to correct your mates at the bar!
HTH
edit: Oops! I just went straight for answering the original quote, and have only now just read the other replies - which of course, were all correct! Go to the top of the class fellas!