Alot of people are using devices before bed. However, this is preventing good quality sleep. Using devices generally prevent you from sleeping, as they stimulate your brain, delaying the release of melatonin, the sleep hormone. Most devices also emit blue light, which can not only temporarily delay your sleep, it can have more permanent affects as it can through of your circadian rhythm, otherwise known as your sleep calendar. When your sleep calendar is affected, you'll start feeling tired later on in the day.