In the first study of its kind, neuroscientists have shown the real-world benefits that sunlight gives the brain, beyond laboratory experiments, linking brighter and more regular daytime light to better alertness and faster attention in everyday life.
The University of Manchester researchers wanted to gain a better understanding of whether sunlight exposure had meaningful cognitive benefits – particularly when tested in nature, not a lab. The team assessed the personal light exposure of 58 UK adults without any significant circadian challenges, over a period of seven days. An additional 41 participants took part in a lab experiment that featured pupillometric and psychophysical tests designed to measure melanopsin-driven visual responses – how their pupils responded to light.
The 58 participants wore a daylight exposure monitoring device on their wrist that continuously recorded how much biologically relevant light reached them, day and night. In other words, how the light influenced their internal body clocks. They also used an app called Brightertime, developed at the university, that gathered data on cognitive performance.
The participants were scored on subjective sleepiness (Karolinska Sleepiness Scale), sustained attention (Psychomotor Vigilance Task), working memory (three-back task) and visual search performance. Each task produced measurable reaction times, accuracy and error rates, later reduced into key factors via a pattern-finding analysis.
“Light is a fundamental environmental cue that governs numerous biological processes in humans, including body clocks, sleep, and cognition,” said lead author Dr. Altug Didikoglu from the University of Manchester. “However, despite substantial findings from controlled laboratory studies, little is known about how these effects translate to real-world environments, where light exposure is dynamic and intertwined with daily routines.”
The team measured aspects of light exposure – how bright the natural light was in the 30 minutes to two hours before each phone-based cognitive test, how bright the day was overall, when the darkest periods occurred (usually when lights were off at bedtime) and how regular or irregular the participants’ daily time in natural light was.
Importantly, the researchers examined both immediate light exposure before each test and broader weekly patterns, which were then compared with the results from repeated smartphone measures of sleepiness, attention, working memory and visual search performance.
They found that how often and when you’re exposed to light in daily life can meaningfully shape alertness and cognitive speed, even in healthy adults with nine-to-five routines or regular night-sleep cycles. But the cognitive impact was more nuanced than this.
Recent light exposure (in those 30 to 120 minutes) was linked to feeling less sleepy and faster reaction times in tests measuring sustained attention and working memory. And the impact was strongest the more recent the light exposure had been (30 to 90 minutes), where reaction speed without increased error rates were observed.
Meanwhile, habitual daytime light exposure – consistent across the seven days – was tied to faster reaction times on the vigilance task and fewer errors in the tests measuring working memory and visual search skills.
People whose light exposure was more stable and less fragmented (fewer switches between light and dark) performed better on visual search tasks, produced fewer attention-related errors and were able to focus for longer.
Brighter recent light was also linked to lower sleepiness at any time of day, but this was strongest in the participants with the brightest light exposure during the day and who also had earlier bedtimes.
“Our findings show that outside controlled laboratory conditions, where participants continue their daily routines, both recent and long-term light exposure positively influences cognitive performance,” said Didikoglu. “The beneficial effects were associated with short-term bright light and habitual light exposure patterns characterized by brighter daytimes, earlier bedtimes, and higher consistency in light exposure.”
In an effort to go beyond observational study, the researchers also looked at the mechanisms that could explain this cognitive functioning change. They looked at the brain’s non-visual light-sensing system, driven by melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). Even though the photopigment melanopsin is in the eye, it doesn’t assist sight as such but uses light to regulate alertness, sleep and circadian rhythms.
These melanopsin-containing cells are especially stimulated by short-wavelength (blue-green) light, which sees them signal to the brain regions involved in circadian timing and arousal. Acute exposure to bright, “melanopic light” is known to increase alertness by influencing the brain’s central clock and other arousal systems downstream of it. In this study, the link between recent light exposure and reduced sleepiness plus faster reaction times is consistent with this short-term arousal mechanism.
Meanwhile, habitual exposure to brighter, more regular daytime light – consistency across the week – is thought to strengthen circadian rhythms and support better sleep–wake cycles. Over time, this may improve attention by stabilizing baseline alertness.
The laboratory cohort of 41 participants were used to measure individual differences in melanopsin sensitivity – hence the pupil tests – and the researchers found no link here. So the researchers believe that the positive cognitive results seen in the real-world cohort and light exposure had more to do with the light than their individual biological makeup.
”Scientists already know that exposure to electrical light at night is known to disrupt sleep quality and delays the biological clock,” said Didikoglu. “Our new study paper now shows that bright daytime light is also critical by supporting cognitive function.
“These improvements in cognitive performance may have practical implications for health, safety, and work efficiency, particularly in low-light workplaces, during extended work hours, or night shifts.”
The study was published in the journal Communications Psychology.
Source: University of Manchester
