Originally Posted by Tits McGhee
The lights onboard are dimmed so that your eyes are used to the darkness, should you be required to evacuate in to the dark outside.
One thing I've never understood is why reading lights are allowed to be turned on at all when the cabin lights are dimmed for take off and landing.
OK, I know it would be terribly inconvenient as everyone wouldn't be able to read their books and papers for 20 minutes of the flight but I often find the glare of the reading light off the paper I'm reading leaves my eyes just as unaccustomed to the dark as when the full cabin lights are on. If the majority of people have their reading lights on then the cabin can actually still be quite bright.
Maybe it just takes my eyes longer to adjust than most people or maybe the whole dimming the lights requirement is a compromise between lowering the light in the cabin a little bit - but not scaring the bejesus out of everyone by making them hurtle through the night sky in pitch black.
Anyone care to, ahem, shed some light on the matter?