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  • A new study suggests that blue light such as from phone screens may not be as disruptive to sleep as previously thought.
  • The study looked at how people reacted to different types of light.
  • They found that between the blue, yellow and white light there was no conclusive evidence that blue was worse than other forms of light.

Light from smartphone screens, tablets, and computers has widely been thought to be disruptive to our natural circadian rhythms. As a result, an industry has sprung up around “sleep hygiene.”

But a new study released last month in the journal Nature suggests that so-called blue light — the type of light emitted from these devices — may not be as disruptive as previously understood.

The study from the University of Basel and the Technical University of Munich, studied “effects of calibrated blue–yellow changes in light on the human circadian clock.” Researchers exposed 16 subjects to three different types of light for an hour before they went to sleep for the night. After using blue-dim, yellow, and constant white background/control light, the study authors determined that there was “no conclusive evidence for an effect of calibrated silent-substitution changes in light colour along the blue–yellow axis on the human circadian clock or sleep.”

Light itself can be a general disruptor to human sleep patterns, but perhaps not in the way that modern devices may have been seen in recent years.

The human eye converts light into electrical impulses via a series of cones, rods, and “so-called intrinsically photosensitive retinal ganglion cells” (ipRGCs). Blue light, which is emitted from devices like smartphones and tablets, is a short-wavelength form of light, and it is converted to the color blue by cones, which respond to bright light; rod cells are only operational in low-light conditions and don’t differentiate between color.

The ipRGCs in the eye receive information about the intensity of light rather than color, and they also keep regular circadian rhythms in check. The photopigment melanopsin, which is expressed by ipRGCs, helps regulate nighttime melatonin suppression. Cones send information to ipRGCS, which suggests that the color of light could affect these regular circadian rhythms and a person’s ability to fall asleep or stay asleep.

A 2019 study suggested that “mistimed light exposure” — namely, the artificial light from devices we use throughout the day — could have detrimental effects on sleep and health. But the process that our brains use to modulate internal circadian rhythms is quite complex, said Dr. Alexander Solomon, surgical neuro-ophthalmologist at Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica.

“There is a master ‘clock’ set by these melanopsin cells (which, again, are still most sensitive to blue light) but other activities such as meal timing and exercise can feed back to that master clock as well,” Solomon told Healthline. “I think if a person is having difficulty regularly sleeping and waking at a regular time needed for their lifestyle, one change could be to either use blue light blocking glasses or a similar phone/screen setting, but it’s also to decrease overall exposure to bright light.”

Solomon said the study’s findings do not mean that people should expect a good night’s sleep if they’re on their phone before bed. Solomon pointed out that the study may not reflect the way most people interact with light in general.

“This study had specifically designed the light exposure…to avoid triggering the light-sensitive cell in our eye known to be responsible for resetting our circadian rhythm, which does not match real-world lighting environments,” Solomon said. “This cell is sensitive to blue light, so saying blue light doesn’t play as much of a role is untrue. It’s simply saying a bright yellow light can affect things as much as a dim blue light.”

Keiland Cooper,Ph.D, a neuroscientist at the University of California, Irvine, told Healthline that the recent study just means more research is needed to fully understand how these devices affect our health.

“While a single study in isolation is rarely conclusive, the main takeaway from present study is that more work needs to be done to further pin down which aspects of screens at night-time negatively impact our sleep,” Cooper said. “Understanding the precise mechanisms of screens on our neural functioning is important because it will help inform device designers and manufactures as to which aspects of their screens may be augmented to aid users sleep and mitigate the side-effects of using our devices.”

Many devices do have a low-light setting that can reduce the brightness of light, and blue-light blocking glasses can reduce the amount of short-frequency waves one is exposed to before bed. But Solomon pointed out that sharp contrasts in exposure to light — and that light’s intensity — may ultimately be a driving factor in how our systems determine sleep schedules and regularity.

“The strongest opportunity for light to set our circadian rhythm comes after prolonged darkness. For example, studies have shown shift workers who work overnight and see the sun while driving home (again, not a blue light specifically, but instead a bright light) have much more trouble sleeping on an appropriate schedule than those who manage to get home and sleep before sunrise,” Solomon said. “I think it’s not something the average person has to consider strongly unless they are having trouble appropriately adapting to the goal sleep/wake times or experiencing excessive daytime sleepiness. There can be many other factors that play a role in difficulty sleeping and seeing a sleep specialist/hygienist may be helpful before attributing it to a single factor such as light exposure.”

“While lowering the intensity of light may help, recommended across countless studies is that the ideal screen-hygiene prior to bed is to avoid them altogether,” Cooper said.

While “screen time” before bed has recently been thought to disrupt natural circadian rhythms, it’s still a bit murky as to how much disruption the light from smartphones and tablets can cause. A new study finds that blue light is not clearly worse for sleep than other forms of light.

Reducing the use of screens before bed is still not a bad idea, given the potential for disruption.

More research needs to be done to fully understand how our systems respond to blue light.