Exposure to brighter and more consistent daylight may help adults fall asleep earlier, wake up earlier, and achieve deeper sleep during the first part of the night, according to a new study led by researchers at the University of Manchester.
The findings, published in the journal NPJ Biological Timing and Sleep, drew on more than 500 days of data from 89 participants who wore light sensors and sleep trackers while maintaining daily sleep diaries. Those with higher daytime light exposure demonstrated healthier sleep timing and increased deep sleep early in the night compared to those with less light.
How daylight influences the body’s internal clock
Jennifer Martin, Ph.D., a clinical psychologist and professor at Florida International University’s Herbert Wertheim College of Medicine, explained that light affects sleep through a biological pathway beginning in the eye. When light reaches specific retinal cells, it signals the brain that it is daytime, promoting alertness.
Morning light, in particular, helps regulate the body’s sleep-wake cycle, Martin noted. She advises spending time outdoors early in the day to reinforce consistent sleep patterns. Limiting bright light in the evening and maintaining a regular wake-up time—with variations of no more than an hour—can also prevent disruptions akin to jet lag, she added.
Study limitations and next steps
The researchers acknowledged that their study identified an association between daytime light exposure and sleep patterns but did not establish direct causation. Additional limitations included the use of wrist-worn devices to measure light exposure rather than direct eye-level assessment, as well as unaccounted variables such as physical activity or meal timing that could influence sleep.
Adults are generally advised to aim for at least seven hours of sleep nightly and to consult a sleep specialist if chronic issues arise. The study authors did not provide further comment beyond the published findings.
