During every ascent that your take on almost every airline in the world you'll notice that the pilots often turn off the cabin lights
. Why do they do this, and is it a safety feature?
After taxiing around, just before takeoff but after the safety demonstration you'll notice that the captain will turn off lights that are in the cabin. This is only done at certain times of the day, and if you aren't aware as to the exact reason for doing so it can be a very peculiar thing. Surely it isn't so safe for passengers who need to escape if the lights are switched off. The only lights that are turned on whether you're flying domestic or catching flights from New York to Berlin is the single LED lights that are on the floor, single dots that lead you all the way to the nearest emergency exit. Those rows have red lights.
The reason for doing it on flights from West Palm Beach to Seattle and practically everywhere is in order to make sure that when it is dark outside that the passengers' eyes are sufficiently adjusted to the darkness. When planes crash they do not tend to just fall out of the sky, but they do sometimes have problems when landing and when taking off. This is why they need to make sure that your eyes are adjusting.
Flights from Boston to Ottawa will rarely if ever crash, but sometimes passengers need to get off of the airplane as quickly as possible, often in darkness. So rather than the passenger struggling to see in the dark, every day on tens of thousands of planes the pilot will dim the lights so that passengers can get off the plane and see where they need to go.