Using an iPad or other backlit electronic tablet in the hours before bedtime not only prevents you from falling asleep, it may also affect your alertness the next day, according to a report published in the Proceedings of the National Academy of Sciences, Dec. 22, 2014. Researchers at Harvard-affiliated Brigham and Women's Hospital found that the light emitted by the devices reset the body's circadian clock, which synchronizes the daily rhythm of sleep to daylight. As a result, people reading e-books took longer to fall asleep and were less alert the next morning than when they read print books instead.
During the two-week study, 12 men and women read digital books on an iPad for four hours before bedtime each night for five consecutive nights. They also followed the same routine using printed books. When they read the iPad, participants were less sleepy before bedtime but were less alert the following morning, even after eight hours of sleep.
If you're a bedtime reader who's addicted to her iPad, don't despair. The researchers used a 2010 iPad set at maximum brightness. Newer iPads and other e-readers have night-reading modes.