In fact, the No. 1 rule is "no computers, cell phones, and PDAs in bed and at least one hour prior to bed time," Dr. Vsevolod Polotsky, who directs sleep basic research in the division of pulmonary and critical care medicine at Johns Hopkins University School of Medicine, told CNN in a recent interview.
That's because "any LED spectrum light source may further suppress melatonin levels," Polotsky said. Melatonin, secreted in a daily 24-hour circadian rhythm, is often referred to as a "sleep hormone," because we sleep better during the night when levels peak.