[topspin]

I've actually worked on blocking all light in one bedroom. This is a great thing when one must sleep during the day.

The one window is thoroughly covered using well fit light blocking material. During daylight there is a very small amount of light the gets in under a door. At night it is utterly black. You may wait as long as you wish for your eyes to adjust; you cannot see your hand in front of your face. Nothing. Activating a smart phone becomes painful.