The blue light that ruins your sleep if you stare at screens before bedtime can be countered with a filter, says an Israeli study that examined how the quality and quantity of slumber is affected by short-wave light.
Short-wavelength blue light – the kind of light emitted in large amounts by laptop, smartphone, tablet, and other device screens – is harmful to sleep, a new joint study by the University of Haifa and the sleep clinic of Tel Aviv’s Assuta Hospital confirms.
But you needn’t be a tech-rejecting Luddite to get a good night’s sleep, according to one of the authors of the study. If blue light is the root of sleep harm, the use of existing filters that prevent the emission of this light, such as a filter that emits a red light, could set things right.
That overuse of device screens is problematic has been established in several previous scientific studies, most notably in a 2015 study at Harvard, which showed that the use of blue screen devices at night disrupted the normal circadian rhythms of the sleep cycle (the 24-hour sleep/wake cycle), which could cause increased levels of cancer, diabetes, heart disease, and obesity in individuals who spend a lot of time with their devices at night.
The new study, published in the journal Chronobiology International, was undertaken by researchers Prof. Abraham Haim, head of the Israeli center for interdisciplinary research in chronobiology at the University of Haifa; doctorate student Amit Shai Green of the Center for Interdisciplinary Chronobiological Research at the University of Haifa and the Sleep and Fatigue Center at Assuta Medical Center; Dr. Merav Cohen-Zion of the School of Behavioral Sciences at the Academic College of Tel Aviv-Yafo; and Prof. Yaron Dagan of the Research Institute for Applied Chronobiology at Tel Hai Academic College.
The researchers sought to examine whether there is any difference in sleep patterns following exposure to blue screen light as compared to red light prior to sleep, and to narrow down what the biggest factor in sleep disruption might be – the wavelength itself, or the intensity of the light. Of all the colors in the visible spectrum, blue light has the shortest wavelength; the shorter the wavelength; the higher the energy. In nature, the shorter blue wavelengths (also known as HEVs, or high-energy wavelengths) collide with air molecules, causing blue light to scatter in the atmosphere (this is why the sky appears blue).
Natural blue light provides the body with many benefits, helping among other things to regulate sleep patterns. Not so for artificial blue light; many devices today utilize LED backlighting, which emits a very strong blue light – strong enough to suppress the production of melatonin, a hormone secreted at night that is connected with normal body cycles and sleep, previous studies have shown. How does this actually affect the body? The University of Haifa/ Assuta study sought to determine how this actually affects the body.
The researchers looked at 19 healthy subjects aged 20-29 who were not aware of the purpose of the study. In the first part of the trial, the participants wore an actigraph — a device that determines the precise moment when an individual falls asleep and awakens — and a daily completed a sleep diary and a questionnaire about their sleeping habits and quality of sleep. In the second part of the trial, which took place at Assuta’s Sleep Laboratory, the participants were exposed to computer screens from 9 p.m. to 11 p.m. – the hours when the pineal gland begins to produce and excrete melatonin. The participants were exposed to four types of light: high-intensity blue light, low-intensity blue light, high-intensity red light, and low-intensity red light.
Following exposure to the light, the participants were connected to instruments that measure brain waves and can determine the stages of sleep a person undergoes during the course of the night, including awakenings not noticed by the participants themselves. Oral temperature and urine samples (for melatonin analysis) were collected from subjects at various times of the night, and in the morning, the participants completed questionnaires relating to their feelings.
On average, exposure to blue light for those two hours reduced the duration of sleep by approximately 16 minutes on average in the subjects. In addition, exposure to blue light significantly reduced the production of melatonin, further affecting sleep quality. However, melatonin production was almost unchanged from normal levels when the individuals were exposed to red light during the evening hours.
In addition, exposure to blue light prevented the body from activating the natural mechanism that reduces body temperature – another factor in sleep disruption and poor quality of sleep.
“When the body moves into sleep it begins to reduce its temperature, reaching the lowest point at around 4:00 a.m. When the body returns to its normal temperature, we wake up,” said Haim. “After exposure to red light, the body continued to behave naturally, but exposure to blue light led the body to maintain its normal temperature throughout the night – further evidence of damage to our natural biological clock.”
Perhaps the most serious finding of the study was that exposure to blue light drastically disrupts the continuity of sleep. After exposure to red light (at weak and strong intensities) people woke up an average of 4.5 times (unnoticed awakenings); but following exposure to weak blue light 6.7 awakenings were recorded, rising to as many as 7.6 awakenings following exposure to strong blue light. Those results correlated with the recorded opinions of participants, who wrote in the questionnaires that they felt more tired and in a worse mood after exposure to blue light.
The secret is in the melatonin – specifically, producing more of it, and to do that, time spent with blue screens must be reduced, Prof. Haim.
“Exposure to screens during the day in general, and at night in particular, is an integral part of our technologically advanced world and will only become more intense in the future,” he said. “However, our study shows that it is not the screens themselves that damage our biological clock, and therefore our sleep, but the short-wave blue light that they emit. Fortunately various applications are available that filter the problematic blue light on the spectrum and replace it with weak red light, thereby reducing the damage to the suppression of melatonin.”