Blue Light May Not Be as Big of a Threat to Sleep as Originally Thought: New Study
Wed, April 21, 2021

Blue Light May Not Be as Big of a Threat to Sleep as Originally Thought: New Study

The last few years have painted blue light as a threat to a good night's sleep / Photo by: Youproduction via Shutterstock


The last few years have painted blue light as a threat to a good night's sleep. This perceived threat is what led experts to warn people from using their mobile phones before going to sleep or advise them to activate night modes in the evening, lessening the blue light their screens emit.

However, a new study from the University of Manchester challenges this belief as it argues that perceived color may also affect people's circadian rhythm. The researchers said the inherent brightness of light exposure may be the actual culprit to confused body clocks—not the color of the light.


The Body Clock

Understanding how blue light affects sleep means one should first understand the circadian rhythm, also known as the body clock, which American digital media company Inverse defines as "the process that regulates hormones, digestion, and temperature." For most people, this process runs for about 24 hours.

The light exposures from sunrises and sunsets help the body clock determine the appropriate times to be asleep and awake. A specialized protein called melanopsin is among the photo-receptors in the eye that filter the light exposure.

It measures the brightness of the daytime light when people wake up and stops the production of melatonin, a hormone that regulates the sleep-wake cycle.

Bright lights keep humans awake throughout the day while boosting attention and mood. When those bright lights dim, melanopsin stimulates the production of melatonin, inducing drowsiness and eventually lulling people to sleep.

However, technological innovations helped light up the world even after the Sun sets. These innovations caused the human body to be more exposed to blue light, especially through device screens and energy-efficient lighting.

According to Inverse, blue light has shorter wavelengths but is more energetic compared to white and yellow lights. This makes it easier for the melanopsin to detect it since it is better at recognizing shorter wavelength photons. This is why earlier studies suggested that blue light is more disruptive to the human body's circadian rhythm compared to other lights. However, researchers from the University of Manchester are questioning this common consensus in their recently published study.

Understanding how blue light affects sleep means one should first understand the circadian rhythm, also known as the body clock / Photo by: feelartfeelant via Shutterstock


Blue Light Is Not the Culprit

The study was carried out on mice and used specially designed lighting, which allowed the team to change the color without changing brightness.

Without changing the brightness, the team found that blue colors produced weaker effects on the body clock of the mice compared to the yellow light colors. The researchers also provided evidence that challenges the melanopsin's ability to detect shorter wavelength photons.

Humans' perception of color is done in the retinal cone cells and the new study demonstrated blue color signals they supplied reduced the effect of light on the body clock.

The researchers said this finding suggests important implications for how light and visual displays of devices are designed to ensure healthy sleeping patterns and alertness.

"We show the common view that blue light has the strongest effect on the clock is [misguided]," Tim Brown, corresponding author on the new study, said in a statement. "The blue colors that are associated with twilight have a weaker effect than the white or yellow light of equivalent brightness."

He added that their findings recommend using dim, cooler lights in the evening and bright, warmer lights during the day so that it will be more beneficial.

"Research has already provided evidence that aligning our body clocks with our social and work schedules can be good for our health. Using color appropriately could be a way to help us better achieve that," Brown said.

Exploring the influence of light

Brown noted the significant interest in changing the effect of light on the body clock by regulating the brightness signals the melanopsin detects.

Current approaches do this by altering the ratio of short and long wavelength light, which gives little difference in terms of brightness "at the expense of perceptible changes in color," the author explained.

"We argue that this is not the best approach, since the changes in color may oppose any benefit obtained from reducing the brightness signals detected by melanopsin."

While the study is not the first to investigate how the chromatic characteristics of light affects the body clock, the New Atlas, a website that provides new technology and science news, says it is the first to explicitly indicate that the perceived color of light is as influential to the circadian rhythm as the spectrums of light regulating melanopsin.

The researchers noted there is no evidence that the perceived color of light has a significant effect on humans' circadian systems, given that their study was conducted on mice, in spite of their confidence that this influence could be observed on people.

Translating the effects found in the study to human beings should be taken with caution. It's clear that blue wavelengths of light stimulate mechanisms that regulate the circadian rhythm in the human brain, but it's unknown if a screen's yellow filter can cause the same effect.

Additional work needs to be done to further understand how different color wavelengths of light affect the human circadian system.