"Why do I have to open my window shade for landing? And why are the cabin lights dimmed?

You are asked to raise your shade so you can see through the window. Not for the view, but to help you remain oriented (which way is up, etc.) if there's an accident. Further, it lets you see what hazards exist outside (fires, debris and such), which would be important during an evacuation. Additionally it lets light into the cabin and makes it easier for rescuers to see inside.

Dimming the lights helps your eyes adjust to darkness, so if anything happens and it goes dark, you're not suddenly blind while dashing for the exits. Also it makes the emergency path/exit lights more visible. These might be the only lights you see in an emergency. And as with the shades, it allows you to see outside for orientation. With the cabin lights burning brightly, the glare would make this impossible."

http://archive.salon.com/tech/col/sm...15/index1.html