The explainations I heard is the shutter are up so in the event of a crash rescue services can see into the plane and also shine lights into the aircraft. The dimming of light is to make your eyes more sensitive so if the plane crashes you can see better. I dont know if these are really true but it is what I have been told by cabin crew. They do sound reasonable but others may know better.

That makes sense Colin - but I shudder at the thought of it.

The actual reason has nothing to do with emergency services, it's all to do with what happens in the event of an evacuation. Firstly, cabin crew and passengers need to be able to see outside. In the event of an incident, you need to be able to see whats happening outside to assess the situation, eg fire, leaking fuel, etc etc to make a decision on which emergency exits to open. You wouldn't want to open doors and evacuate in to a fire or a pool of aviation fuel. Do a search for the Air France crash in Toronto, it was the quick decision making by cabin crew that saved the lives of everyone on board. Secondly, if it's light inside the aircraft and dark outside, it can take a while for your eyes to adjust. If your eyes are already adjusted to the dark and light outside, then you'll be able to see your evacuation route immediately. In an incident, power loss and therefore lighting will fail quickly. Try having your lights on in the house then turning them off in to complete darkness and see how long it takes to be able to see anything. Seconds count. It's difficult to see inside an aircraft from the outside because of the small size of the windows, often glare and it being dark inside. Looking through windows takes time to do and often need ladders to get to windows. Emergency services wouldn't have time for that and would aim for doors. It's all to do with being prepared to evacuate the aircraft as short notice.

Darren

Dazbo, good explanation but if dimming cabin lights is for safety in case of evacuation, why do airlines allow you to switch on the light above your seat to read during take off and landing? I'd have thought that it'd be better to not allow the lights above seats to be on until plane is airborne.

That's a very good question! They must deam personal lights as acceptable as they aren't as bright as cabin (ambient) lights. There's also the question or risk v comfort. The risk of a problem during take off and landing in modern aircraft is small so it's a trade-off with passenger comform and enjoyment I suppose.

Darren

Didn't think of that.