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The team at Osaka Municipal University has discovered a way to combat that groggy feeling many of us experience in the morning. The researchers found that just 20 minutes of exposure to sunlight before waking can keep you energized throughout the day.
They say most people feel morning fatigue even after a full night’s sleep. This condition can be eased with physical exercise and by limiting food and alcohol intake before bedtime.
However, the team found that a brief exposure to natural light right before waking is especially effective for shaking off sleepiness.
Waking Up to Natural Light is Better Than Artificial
Previous studies have shown that exposure to artificial light that mimics a natural sunrise can also reduce morning fatigue. However, that method has downsides.
“Dawn is typically simulated by small light sources placed on a bedside table, which are quite low, usually at eye level,” their report says. Moreover, these devices tend to aim their beams in one direction. One workaround is diffusing the light by mounting a dawn simulator on the ceiling. But why do that when, in most populated areas, dawn happens naturally and provides a free way to help us wake up refreshed?
For people who live where there’s little light pollution, leaving curtains or blinds open at night can let them enjoy darkness until dawn. But not everyone has that option because of street lighting, Science Alert reports. Some solve the problem with devices like motorized curtains that block light at night and open at a set time each morning.
How Was the Study Conducted?
The researchers recruited 19 university students aged 20 to 30. Participants reported that on weekdays they typically went to bed between 11 PM and 1 AM and woke up between 7 AM and 9 AM.
The volunteers slept in a university laboratory set up like a bedroom. All windows were covered except for one facing east, which served as the room’s only source of natural light.
On that east-facing window, the team installed light-blocking curtains and a motorized device that slowly opened them each morning at a set time.
This setup let the researchers test three scenarios. In the first, sunlight entered the bedroom 20 minutes before waking. In the second, natural light filled the room from dawn until waking. In the third, the room stayed dark until waking.
After participants woke in each simulated situation, the researchers measured their sleepiness, alertness, and fatigue.
Objective alertness (measured using an electrocardiogram) and self-reported sleepiness were significantly better in the two conditions with natural light compared with the dark condition.
Still, timing and the amount of natural light mattered most. Objective sleepiness, measured with an electroencephalogram, was significantly lower after 20 minutes of natural light exposure before waking than in the other scenarios.
The team suggested that prolonged sunlight from dawn until waking could actually impair sleep quality.
Daisuke Matsushita, the lead author of the study, said future research based on these findings will explore the most effective ways to use sunlight to fight sleepiness.
“In the future, we hope to control natural lighting in the sleep environment, as it varies with the seasons and times of day, and to determine how to provide natural light for a more comfortable awakening,” Matsushita said.
The results were published in the journal Building and Environment.
