You have to sleep in the dark! Melatonin, the so-called sleep hormone, commands this. This hormone is produced in a tiny organ weighing only one gram! The pineal body. We won't focus on its functions - they are so numerous😁 Let's concentrate on melatonin. As soon as total darkness sets in and our visual receptors pick up on this, melatonin is produced. That's why it's not okay to sleep with the lights on and it's not healthy to have a nighttime routine. If it is unavoidable, we should at least provide minimal light during daytime sleep. By the way, interestingly enough, melatonin is formed from the "happiness" hormone seratonin.