Study: E-readers, tablets can disrupt sleep

The blue-heavy light of electronic devices can throw off circadian rhythms

Science may have confirmed what parents of gadget-loving children have long suspected: Using light-emitting gadgets just before bedtime can interfere with sleep.

Using an electronic book reader or another portable electronic light-generating device prior to going to sleep can disrupt regular sleeping habits, researchers at Pennsylvania State University have found.

"The take-away is, however unpopular, to avoid use of these devices before bedtime," said Anne-Marie Chang, an assistant professor at Pennsylvania State University's Department of Biobehavioral Health, one of the authors of the study.

The researchers will publish their findings in the December 23 issue of the Proceedings of the National Academy of Science.

For the study, 12 participants read iPads in dim light for four hours prior to falling asleep for five consecutive nights. Then, for five nights, they read a paper-based book in a similar setting. They were outfitted with instruments to measure their eye movements, heart rates, and other physical cues.

"We knew from other published reports that light can affect sleep, so we wanted to know what kind of impact light from these electronic devices specifically would have," Chang said.Compared to those evenings when they read books, participants who used the electronic devices prior to bedtime took almost 10 minutes longer to fall asleep, the study found. They also weren't as drowsy in the evening, and were sleepier in the morning.

By reading on electronic devices before regular sleep time, the participants shifted their bodies' typical circadian rhythms, the researchers posited. Circadian rhythms are the biological clocks that signal to humans, and other organisms, when to fall asleep. The researchers had collected blood samples every hour they were asleep to measure melatonin.

The researchers also measured the light intensity from iPads, iPhones, Kindle Fires, computer laptops, and the Barnes And Noble Nook Color electronic book readers, and found them all to be approximately equal in terms of luminescence.

They also found that the light these devices emit has a higher concentration of blue light -- with a frequency of around 450 nanometers -- than the color balance we typically experience in natural light.

For those who feel they need to read electronically before slumbering, Chang advised using a device that does not emit light, such as one of the Amazon Kindle models without backlighting. Also worth investigating are screen overlays, or filters, which are sold by a number of companies and minimize the amount of blue light transmitted from portable devices.

Joab Jackson covers enterprise software and general technology breaking news for The IDG News Service. Follow Joab on Twitter at @Joab_Jackson. Joab's e-mail address is

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Joab Jackson

IDG News Service
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