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A new study has claimed that light-emitting e-readers “negatively affect sleep, circadian timing and next-morning alertness” when used in the evening. However, those reading the resulting coverage should look into the details before worrying too much.
The study was published Monday in the Proceedings of the National Academy of Sciences (PNAS), leading to scary headlines such as: “E-readers ‘damage sleep and health,’ doctors warn” (BBC); “Keep That E-Reader Out of Bed and You’ll Feel Better in the Morning” (Pacific Standard); and “Before Bed, Switch Off The E-Reader And Pick Up A Paperback” (Fast Company).
The key problem with this study and the more alarmist stories that followed, is that when it says “e-reader”, it means “[company]Apple[/company] iPad”. An iPad at full brightness, no less. When I hear “e-reader”, I tend to think “dedicated e-reader” – an e-ink device without a backlit screen — rather than a multi-purpose tablet. And there’s a big difference.
The screens of devices such as tablets and smartphones have long been known to emit short-wavelength light, also known as blue light. All light can suppress the secretion of melatonin – the hormone that controls our day-night cycles – in the evening and night-time, but blue light has a particularly pronounced effect and previous studies have shown that it’s best avoided at night.
The new study, conducted on a small group of 12 participants, adds to these earlier studies by comparing the effects of a light-emitting “e-book” (iPad) with those of a paper book. The researchers found printed books were definitely safer, writing:
The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently. We found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning. Use of light-emitting devices immediately before bedtime also increases alertness at that time, which may lead users to delay bedtime at home. Overall, we found that the use of portable light-emitting devices immediately before bedtime has biological effects that may perpetuate sleep deficiency and disrupt circadian rhythms, both of which can have adverse impacts on performance, health, and safety.
These effects could be serious. As the researchers note, recent evidence has linked chronic suppression of melatonin secretion by nocturnal light exposure with “the increased risk of breast, colorectal, and advanced prostate cancer associated with night-shift work… which has now been classified as a probable carcinogen by the World Health Organization.”
But again, there’s a huge difference between an iPad and an e-ink reader such as those in the [company]Amazon[/company] Kindle, [company]Kobo[/company] or [company]Barnes & Noble[/company] Nook ranges. The study does not once mention e-ink e-readers. The iPad was also “set to maximum brightness throughout the four-hour reading session, whereas, by comparison, the print-book condition consisted of reflected exposure to very dim light.”
Charles Czeisler, director of the Division of Sleep Medicine at Harvard Medical School, who co-authored the study, told the Washington Post that the “standard Kindle” would provide an exception to the study’s findings as it does not emit light and was more like reading a paper book. A Vox interview with lead author Anne-Marie Chang suggests that the research was conducted between 2010 and 2011, when even the original, non-illuminated Kindle was pretty new and paper books made a better point of comparison.
There has been no mention at all of e-ink readers that are not backlit but that are illuminated, such as the Kindle Paperwhite or Nook GlowLight — which is not surprising as these devices were only introduced in 2012. Rather than lighting the screen from behind, illuminated e-ink e-readers are “front-lit” and use small LEDs around the screen, pointing inward rather than outward, to cast a glow over it (the Paperwhite channels this through “light guides” to illuminate evenly). This is more like looking at an earlier Kindle in a lit room, than it is like looking at a light shining directly into your eyes.
What’s more, these devices generally allow users to dim the light – and so do blue-light-tastic backlit tablets, for that matter.
So in short, yes, you should avoid staring at your smartphone or tablet (or PC or TV) for hours before trying to nod off. And that includes the Kindle Fire, which is after all just a tablet. But let’s give dedicated e-ink e-readers, which are very different devices, the benefit of the doubt until someone proves they also pose a danger.