A new study, in an effort to understand the effects that light might have on sleep, has found that people who read from a tablet right before going to bed have different electrical brain activity than people who read a physical book.
Researchers at the University of Bergen in Norway recruited 16 participants between the ages of 22 and 33 who were not smokers and did not suffer from any sleep, medical or mental conditions. Before the start of the study, the participants were asked to follow a normal sleep-wake schedule for one full week. The three-night study began after the week ended.
During the first night, the participants slept normally while the researchers used polysomnographic recording, which included electroencephalograms (EEG), to monitor the participants' brain activity and other factors of sleep.
The researchers used the same method to record the participant's activity during nights two and three, when the participants were required to either read from an iPad or from a physical book using normal light for 30 minutes before going to sleep. They also used a light meter to measure illumination at eye level. All of the participants slept in their own beds.
The team found that even though illumination levels were about 50 percent higher when the participants were reading from an iPad than when they were reading from a physical book, it still took the participants the same amount of time to fall asleep on both nights. The participants also slept for about the same length of time regardless of what they were using to read.
In terms of self-reports of sleepiness, participants were more likely to report feeling sleepy after reading a book. To examine this further, the research team looked at the EEG readings and found that slow wave activity was delayed and reduced after using an iPad. Delayed activity can negatively affect the restorative properties of sleep.
"We found a delay of 30 minutes in the generation of the restorative slow waves during sleep in the iPad condition," said lead study author Janne Gronli of the University of Bergen in Norway. "Slow wave sleep EEG activity is important for the restorative effect of our sleep."
The team acknowledged that a limit of the study was the fact that the scientists only analyzed one night of sleep for each condition. The study also used a very small sample set.
"We only examined one night using an iPad," Gronli said. "It is tempting to speculate that daily use of an iPad, and other blue light emitting electronic devices, before bedtime may have consequences for human sleep and cognitive performance."
While the researchers did not find a cause-and-effect relationship, they are recommending that people use the bedroom for sleep and not for work.
The study was recently published in the journal Sleep Medicine.
