Health experts have known for some time that exposure to light helps to regulate the body's internal clock. That's why humans get sleepy when it's dark outside and start to wake when it's light out. Research has found that it may be more than light affecting our circadian rhythms; it may be the color of that light that really makes a difference.
And that color is the one we see a lot of, whether it's in the sky, from our various electronic devices or even from our lightbulbs.
Hard to sleep with the blues
We've known for some time that blue light can mess with our bodies' internal clocks. A study published in the Proceedings of the National Academy of Sciences found that our light-emitting e-readers were disrupting our sleep by suppressing the melatonin production in our bodies and increasing a sense of wakefulness. That study had people read from iPads or from regular books and discovered that those who read from iPads had a harder time falling asleep and had less REM sleep when they finally fell asleep.
Another study, published in the journal PLOS Biology, looked at how mice were affected by the color of the light they were exposed to. Specifically, researchers wanted to know if the color of light affected the suprachiasmatic nucleus — the part of the brain that helps vertebrates regulate time using electrical and chemical signals. So instead of just testing how the mice slept when exposed to certain kinds of light, researchers also checked their body and brain reactions.
To test this, the University of Manchester researchers exposed mice to various colors and intensities of light while measuring nerve signals in the suprachiasmatic. Using an artificial sky, the mice were tested at various intensities of light, from bright light to complete darkness. And they were also tested when they were exposed to colors of light, such as the pinks and oranges that one might see during sunrise and sunset.
Researchers found that when the mice were exposed to light, as well as the various colors of light, they behaved perfectly normally. But when they were exposed to light that went from bright to dark without the color cues, their suprachiasmatic nerve signals lagged behind by about 30 minutes. Other physiological changes — such as a drop in body temperature — that might indicate the mice were ready to sleep also lagged behind by 30 minutes without exposure to colors.
So what does all of this mean for humans? It's possible that it doesn't mean a thing. But other sleep studies that have looked into changes within the suprachiasmatic have noted a strong correlation between reactions in mice and those in humans. And if humans are affected by the color — and not just the intensity — of light, it may help health experts create better treatment options from those who suffer from sleep disorders, even minor ones such as jet lag.
Another color perspective
Interestingly, a more recent study — also conducted by University of Manchester researchers — suggests that blue light may not be as disruptive to sleep patterns as originally thought.
The study, which was published in Current Biology, found that blue light had weaker effects on mice body clocks than equally bright yellow lights. For the study, the researchers adjusted the color without changing the brightness.
The findings suggest that using dim, cooler lights in the evening and bright, warmer lights during the day might be better for health.
“We show the common view that blue light has the strongest effect on the clock is misguided," study author Tim Brown, said in a statement. "In fact, the blue colors that are associated with twilight have a weaker effect than white or yellow light of equivalent brightness."
But these findings are relatively controversial compared to most research on blue light.
A Harvard-produced summary of blue light's impact on sleep reinforces the concerns of blue lights as a melatonin suppressor, citing two different studies about blue light, including one that exposed people to 6.5 hours of blue light and 6.5 hours of green light. The former suppressed melatonin production twice as long as the latter.
The summary also highlighted the potential to our sleep cycles posed by LED light bulbs, many of which can emit more blue light than bulbs have in the past.
Correcting the blue
There are ways to counteract the effects of blue light, though not all them may be appealing.
On a very basic level, simply reducing your exposure to blue light before sleep should help. The Harvard summary mentions that avoiding looking at bright screens two to three hours before bed can make a difference, so that means minimizing your phone, tablet and TV time before hitting the sack.
If that doesn't work, a study published in the Journal of Adolescent Health found that when young people (under the age of 20) wore orange-tinted glasses at night while looking at the screens, they felt more sleepy than those who wore nothing or their regular, clear-lens glasses. The Harvard summary backs that up, recommending wearing blue-blocking glasses if you work a night shift or need to use electronics frequently at night.
Of course, orange-tinted glasses may not be conducive to your lifestyle or your personal aesthetic, even if it does mean a better night's sleep. Ultimately, screens that don't use as much blue light may be the best way to get better sleep. A small study published in Sleep, and conducted by some of the same University of Manchester researchers mentioned earlier, outlines the benefits of a screen that allows the user to control the amount of cyan in an image.
A normal display uses red, green and blue to create the colors we see on displays. The researchers added cyan to the mix to create a "melanopic display." When the eleven participants in the study upped the amount of cyan on the screen, they felt more awake. When they lowered the amount, they became sleepier. The addition of cyan even seemed to improve overall image quality.
Researchers also measured the amount of melatonin in the participants' saliva, and they found higher concentrations when cyan was at a lower setting.
"This outcome is exciting because it tells us that regulating exposure to cyan light can influence how sleepy we feel," the study's lead author, Rob Lucas, said in a statement. "Our study also shows how we can use that knowledge to improve the design of visual displays. We built our melanopic display by adapting a data projector, but we would expect that this design could be applied to any type of display."
If only we had this sleepy-time smartphone screen now.
Editor's note: This story has been updated with new information since it was originally published in April 2015.