You can forget the “no screens, no exercise, no snacks” bedtime rules that are designed to provide teens with good sleep. Sleep hygiene refers to a set of habits, behaviors and environmental factors that promote and maintain good sleep. For teens, the so-called “cardinal rules” of sleep hygiene are: no screens, physical activity, or food in the hour before bed. Screen use before bed didn't change sleep length or quality, it just took kids 20 minutes longer to go to sleep DepositphotosThey found that 99% of participants used screens before bed on most nights. On the nights they did exercise, kids got about 34 minutes more sleep, though this wasn’t tied to other sleep measures.