Why is it hard for most people to sleep if it’s not completely dark?

Question

Edit to add: Maybe *completely* dark wasn’t the right wording, but like, why do people generally prefer sleeping in the dark, why does that affect your ability to fall asleep in many cases?

In: 5

Answer 1

A hormone called Melatonin, production increases with darkness, making you sleepy and fall asleep.
As the sun comes up, or with most bright lights, melatonin production decreases, thus waking you up.