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Blue Light Hazardous to Sleep, but Helpful While Awake

Artificial light is a hazard to sleep, but beneficial to daytime function.

We’re continuing to learn more about the stimulating effects of blue wavelength light and its capacity to disrupt sleep. Exposure to artificial light at night is recognized as a hazard to sleep, contributing to rising rates of disrupted and disordered sleep. Different wavelengths of light have been shown to affect human physiology and sleep cycles in different ways. Blue light, a short-wavelength light, has been singled out as more significantly disruptive to sleep than other colors on the light spectrum. Research has shown blue light delays release of the sleep hormone melatonin, disrupts circadian rhythms, and may influence negative changes to mood.

In our pursuit of energy efficiency, we’re finding ourselves exposed to greater amounts of blue light than ever before. High-efficiency light bulbs, as well as digital devices including smartphones, tablets, and computers, emit high concentrations of blue light. Blue light appears to be uniquely detrimental to our sleep. But can it also be singularly beneficial during to our waking lives?

A new study further examines the stimulating effects of blue wavelength light, focusing on the effects of daytime exposure to the short-wavelength light. Researchers at Boston’s Brigham and Women’s Hospital and Philadelphia’s Thomas Jefferson University investigated the effects on alertness and cognitive performance from prolonged daytime exposure to blue light. They also compared the daytime effects of blue light exposure to the effects of evening exposure to the same degree of light. Their findings confirm that blue light at night stimulates alertness and diminishes feelings of drowsiness, interfering with sleep. Exposure to blue light during the day, however, results in a similar, more welcome boost to alertness and reduction to fatigue, which stand to benefit both daytime function and nighttime rest.

The study included 16 healthy young adult men and women. To evaluate the impact of blue light in the day and evening, researchers compared the stimulating effects of blue wavelength light to green wavelength light. Participants were exposed to equal amounts of blue light or green light for a period of 6.5 hours in the middle of a 16.5-hour waking day. Researchers measured fatigue, alertness, and performance using ratings from participants themselves, as well as tests to measure attention, response, and reaction times. Researchers also measured brain activity during periods of light exposure using EEG. Their results indicate that across all measures, extended exposure to blue light during both day and night significantly increased alertness:

  • People exposed to blue light during the day reported less sleepiness than those exposed to green light during the same daytime period.
  • People exposed to daytime blue light displayed quicker reaction times, higher levels of alertness, and greater attention spans in performance tests, compared to people exposed to green light.
  • EEG tests showed alterations to brain activity that indicated heightened alertness among people exposed to blue light during the day.

The nighttime effects of blue light exposure were also significantly more potent than green light exposure, in ways that are disruptive to sleep:

  • People exposed to blue light at night reported feeling significantly less sleepy than those exposed to green light in the evening hours.
  • EEG results showed heightened alertness among people exposed to blue light in the evening.
  • People exposed to blue light at night scored higher on attention and reaction performance tests than people exposed to green light during the same period.
  • Overall alertness among people exposed to blue light at night was nearly as high as daytime levels of alertness.

These results suggest that blue light spurs alertness and reduces sleepiness in ways that are detrimental to sleep at night but may be beneficial during waking hours, in improving daytime performance and reducing daytime fatigue. What’s more, this boost in daytime alertness and decrease in sleepiness may actually help improve sleep at bedtime. Most of the research into the effects of blue light has focused on its capacity to disrupt sleep. This is one of the first studies to explore the possible benefits of blue light to daytime functioning. There is limited earlier research that supports these current results, including a 2008 study conducted in the United Kingdom. Office workers who were exposed to blue light in the morning experienced both a reduction to daytime sleepiness and improvements to the quality of their nighttime sleep, according to the results of that investigation.

These current finding also indicate that blue light hinders sleep in ways beyond the delayed release of melatonin, and alteration to circadian rhythms. Exposure to blue light at night spurs cognitive function and alertness in ways very similar to daytime stimulation, a change that can make sleep significantly more difficult to achieve.

Exposure to artificial light at night—especially to the high concentrations of blue light coming from digital devices—will interfere with the ability to sleep. Too often, these devices find their way into our bedrooms, in many instances even to be used as alarm clocks. The presence of artificial light from devices like smartphones and tablets in the bedroom poses a challenge to the darkness that is so important to normal circadian rhythm function. This nighttime light intrusion also stimulates alertness and brain activity that is counterproductive to the mind and body’s natural pull toward sleep.

We’re at the relative beginning of our understanding of how different forms of light affect sleep and health—and how light might be manipulated not only to protect sleep but also to enhance waking performance. With new technologies appearing to help provide effective lighting during the day and provide solutions for the effect of light’s interference before sleep, these issues only stand to grow in importance. As we continue to explore the effects of exposure to different forms of light, we may find that blue light poses both problems and solutions for sleep.

Sweet Dreams,

Michael J. Breus, PhD

The Sleep Doctor™

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