Studies show that light promotes wakefulness and that computer screens and small electronic devices can miscue the brain and promote wakefulness. Photoreceptors in the retina signal our brain about the outside world when they sense light and dark.
Sensing light and dark helps align circadian rhythms to the cycle of day and night, helping people be alert in the morning and fall asleep at night.
Studies show that children who use electronic media as a sleep aid have later weekday bedtimes and fewer hours of sleep per week. They also report more daytime sleepiness. Adolescents who have a television in their bedrooms have later bedtimes, more difficulty initiating sleep and shorter total sleep times. Self-reported daytime sleepiness dramatically increases when texting and emailing happens after lights out even once per week.