Here are a few tips for sleeping in darkness for a better sleep

Installing blackout curtains on bedroom windows keeps outside light from disturbing your sleep.
These window coverings should be heavy enough to block the outside light completely, and should be properly fitted to your windows so slivers of outside light do not filter in.

Eye masks worn at night can help to deepen the darkness of your bedroom and prevent light from entering your bedroom. As a result, your bedroom should be as dark as the moonlight on a clear evening.