If you are going to read about the benefits of sleeping in total darkness, you will encounter the words: pineal glands, melatonin, circadian cycles, cancer, and many more.
But just to simplify, here goes: sleeping in total darkness helps regulate your sleep pattern. To make things complicated, an endocrine gland found in our brain which is called pineal gland produces melatonin during sleep time and produces more in the absence of ANY light. Melatonin is a hormone responsible in modulating sleep pattern.
In short, melatonin normalizes your sleeping time and waking time.
So turn off your lights and let Prince Phillip find you in the dark.
Who can share their knowledge on why a regular sleep schedule benefits our health?
Extra: Natural (moonlight) or artificial light, led or low-emitting night lights, any light at all, will affect the production of melatonin.