Use of a light-emitting electronic device in hours before bedtime can adversely impact overall health, alertness, and the circadian clock which synchronises the daily rhythms of sleep to external environmental time cues, according to researchers at Brigham and Women's Hospital, who compared the biological effects of reading an LE-eBook compared to a printed book.

"We found the body's natural circadian rhythms were interrupted by short-wavelength enriched light, otherwise known as blue light, from these electronic devices," said Anne-Marie Chang, PhD, corresponding author, and associate neuroscientist in BWH's Division of Sleep and Circadian Disorders.

"Participants reading an LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book."

Source: http://sciencedaily.com