Story At A Glance

  • Studies show that using screens shortly before bedtime can make it harder to fall asleep, largely because of the blue light.
  • Children, who tend to have more sleep needs, are even more at risk.
  • Although it’s difficult, you have to limit screen time before bed.
  • You can also try blue blocker glasses or other methods to get more rest.

You can’t help it. Screen time has become a part of not only your daily life, and your children’s lives as well. Yet you may have also heard about potential harm from the resulting blue light and how it can cause eye strain and affect your sleep. With so much of our lives now dictated by screens, what was evolutionarily an adaptive response to light has become something to worry about.

How light affects our bodies

It’s been well documented that light affects circadian rhythms — biological processes that regulate the sleep-wake cycle every 24 hours — in humans and other living things. But our circadian rhythms can be thrown out of whack by changes in exposure to light and by our behavior. For example, in early experiments in the 1950s, participants that were free to control their light situation and sleep schedule tended to adhere to cycles longer than 24 hours. Meaning, their schedules for an ideal day lasted longer than the 24-hour day we are normally given by the rotation of the Earth.

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A person can delay or reset their circadian rhythm like they can reset a watch. And that’s due to how our bodies respond to light. For shift workers who work night shifts, that is a good thing. But that doesn’t necessarily mean they are able to completely avoid negative side effects.

Light makes us alert and attentive, especially blue light. Melanopsin retinal ganglion cells, a type of light receptor in our eye, responds to blue light. And from what we know, it signals to a part of the brain called the suprachiasmatic nucleus (SCN), which acts like a master clock. The melanopsin cells were discovered in 1998, and further research with animal models into the early 2000s established their role in setting the circadian rhythm. When the light receptors are actively responding to blue light, they signal to the SCN, keeping our brains active and alert. It also suppresses the production of melatonin, the hormone that regulates sleep. 

This is all great and lovely when humans live by the light we get from the sun. But as civilization has become more and more advanced, we have more and more sources of light, including blue light. As we use those sources of light later and later into the night and because our brain is getting the signal that there’s light and we should be active and awake, our sleep-wake cycle is thrown off.

Kids, screen time and sleep

When it comes to children, they have different sleep needs than adults. Young children about one to four years old typically need 10 to 14 hours of sleep per day, including naps. Tweens might need around 9 or 10 hours. By the time they get to high school, that drops down to 8 or 9 hours. But teenagers also experience a shift in their circadian rhythms, brought on by puberty. So they may stay awake much later at night and sleep later into the morning. But because school schedules may require them to get up early, they may not get the hours they need.

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How does screen time fit in with all of this? By using blue light-enriched screens in the evening hours, “there is a big potential for [the sleep phase] to be delayed by this artificial light exposure,” says psychologist Christina Schmidt of the University of Liège in Belgium. For example, a 2014 study by Harvard researchers comparing people who read from paper books and from screens found that screen users secreted less melatonin and had a delayed circadian rhythm of more than an hour. There’s also some amazing research in blind people that found they can still detect light even if they can’t see it, and that their brains respond to blue light.

A 2015 study that gave blue light-blocking glasses to male teenagers for one week found that the blue blockers helped to lower the effect of blue light on suppressing melatonin, meaning they were able to produce melatonin and start the bodily processes for sleep. Overall, the participants experienced decreased “vigilant attention and subjective alertness” before bedtime. While this study only looked at short-term effects and only in male teenagers, a longer-term study would be able to help us understand the chronic impacts of blue light and in a wider population, says Schmidt, who was a coauthor on the study.

However, it’s unclear how much blue light affects our sleep quality. Research suggests that, while blue light can affect how well you signal to your body that it’s sleepy time, it may or may not affect your quality of sleep. The teenagers in that study who used blue blockers didn’t seem to wake up any different from teenagers who got the control treatment (clear lenses). In a different study, researchers found that sleep structure, like rapid eye movement and non-rapid eye movement cycles, was affected by blue light exposure prior to going to sleep. 

What you can do

It might be possible to adjust how much blue light your device emits or put a physical screen filter over the device to reduce the amount of blue light. Many people are also switching to “night mode” in which screens show less white spaces and show more dark colors.

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Blue blocking glasses generally do seem to work to help people sleep better. In a 2018 study, people with insomnia who wore amber glasses for two hours before bedtime for a week were able to improve their sleep. But these types of glasses should be used with caution, Schmidt adds. For example, if you are working the night shift and then driving home, blocking blue light during work hours could be detrimental to being awake enough to drive home safely.

Schmidt recommends limiting exposure to artificial light in the evening and increasing exposure to light in the morning to help consolidate sleep to the right timing. And if you do choose to use blue blockers, take into consideration that light does have an important role for signaling to our brains when we should pay attention.

While more research is needed to determine whether blue light is harmful to kids and young adults in the long term, the research shows that it’s counterproductive to getting to bed on time and can delay the circadian rhythm. So, if you are one of those people who needs at least a full eight hours, then it’s in your best interest to limit blue light exposure in the evening. It might be time to invest in blue blockers for the whole family, or you can go the old-fashioned route and turn off your screens well before you hit the hay.

Published on Nov 11, 2019