LULU GARCIA-NAVARRO, HOST:
The light coming from screens, like the one on your smartphone, is known as blue light, and it can interfere with sleep. So some people use apps to filter out some of that blue light. NPR's Jon Hamilton had some questions, so he rang up some scientists.
JON HAMILTON, BYLINE: The first person I called is Lisa Ostrin at the University of Houston College of Optometry. She studies the effects of blue light on sleep. She also owns an iPhone. And every iPhone comes with an app called Night Shift that lets you filter out blue light. So I asked Ostrin, do you use it?
LISA OSTRIN: Yes, I do.
HAMILTON: Ostrin says without a filtering app, cell phones and tablets expose people to a lot of blue light.
OSTRIN: Especially as people are laying in bed and have their screens just a few inches from their face before bedtime.
HAMILTON: And Ostrin says all that blue light prevents photoreceptor cells in the eye from triggering the release of an important hormone.
OSTRIN: Normally, when the sun goes down and the lights turn off, our body releases melatonin, which helps us get a nice restful sleep. But when we have all this artificial light on, it's tricking those photoreceptors into thinking it's still daytime.
HAMILTON: Ostrin's own research has shown that it's possible to prevent this. She had 21 people put on special glasses after sunset each day to filter out blue light.
OSTRIN: So, essentially, we blocked the input to those receptors that tell our body it's still daytime.
HAMILTON: And it made a difference.
OSTRIN: What we found was a dramatic increase in their nighttime melatonin levels after two weeks of wearing these glasses.
HAMILTON: Participants also reported better sleep. To get another perspective, I called Brian Zoltowski at Southern Methodist University in Dallas. Like Ostrin, he studies blue light and sleep, and he owns an iPhone.
BRIAN ZOLTOWSKI: I am talking to you on an iPhone right now. And I actually am not a Night Shift user currently.
HAMILTON: Zoltowski says he did use the filtering app. He also took steps to reduce the blue light coming from other screens during the evening. And he says that made every image look kind of orange.
ZOLTOWSKI: So I'm looking at an orange screen watching a video, realizing also drinking a cup of coffee. And it started to make me wonder then why I'm actually trying to, you know, decrease the amount of blue light when the caffeine that I'm drinking - my cup of coffee is probably having a larger effect on my sleep quality.
HAMILTON: Also, he really didn't like all those orange screens.
ZOLTOWSKI: I'm willing to take the blue light exposure for the improved quality of the images.
HAMILTON: Zoltowski adds that devices are just one source of blue light. Others include indoor lighting and street lights. So he says a filtering app may not be worth it, especially if you're already getting a good night's sleep.
ZOLTOWSKI: But if you suffer from sleep problems and you've tried other things like eliminating caffeine later in the day, this is something that you can add to your kind of repertoire of making sure that you're doing everything you can to promote a healthful sleeping environment.
HAMILTON: Zoltowski says you might also just give up screens entirely around bedtime. At least one study found that people got more sleep when they switched from electronic readers to printed books. Jon Hamilton, NPR News.
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