Could a Lack of Sunlight Be Affecting Your Brain? What New Research Found
Could spending too little time in sunlight affect your brain? New research explores the relationship between daylight exposure, cognitive performance, attention, and the environments where we spend our days.
BY Benedito Albuquerque
Could a Lack of Sunlight Be Affecting Your Brain?
You can go through an entire day without thinking much about sunlight.
You wake up, turn on a light, work in front of a screen, move from one indoor space to another, and perhaps only notice the daylight when you finally step outside.
Modern life makes this surprisingly easy.
But daylight is not simply something that helps us see. It is also an environmental signal that interacts with biological rhythms, alertness and, potentially, cognitive performance.
A new study published in September 2026 has brought this question back into focus. Researchers examined data from two large UK national cohorts and found that short-term sunlight exposure was associated with performance on several cognitive tests, particularly when overall solar radiation was relatively low.
That does not mean that sunlight is a magic cognitive enhancer, or that staying indoors automatically damages the brain.
The finding is more interesting than that.
It raises a question that architects should take seriously:
What happens when the environments where we spend most of our time give the brain very little contact with natural daylight?
What the New Study Actually Found
The 2026 study by Andrew Stevenson and Chris Dibben, of the University of Edinburgh, was published in Photochemical & Photobiological Sciences. It used information from two UK national cohorts: the UK Household Longitudinal Study, with more than 40,000 adults tested between 2011 and 2013, and the 1958 National Child Development Study, in which about 11,700 sixteen-year-olds were tested in 1974.
The researchers linked each person's test date to the solar radiation measured by weather stations in their region on the day of the test and the day before.
Here is the clever part of the design.
They compared people tested on brighter and duller days within the same month and the same day of the week, so seasons and calendar effects were not mixed up with the sunlight effect.
In the adult cohort, higher solar radiation was associated with better:
- general cognitive ability;
- immediate word recall;
- delayed word recall;
- verbal fluency.
There was no association with number series, a task that measures abstract reasoning. In the teenage cohort, similar patterns appeared for reading comprehension and mathematics.
The relationship was not simply "more sunlight equals better cognition."
The associations were strongest at lower levels of solar radiation, similar to conditions commonly experienced during autumn and winter in the UK. Beyond roughly 8 to 10 megajoules per square meter per day, closer to spring and summer conditions, the relationship flattened or disappeared for most outcomes.
That detail matters.
It suggests that the relationship between sunlight and cognition may be nonlinear, rather than a simple case of more being better.
It also matters how large the differences were. Compared with the darkest days in the data, brighter days were associated with small gains: about a quarter of a word more in delayed recall (2.5% of the test range) and roughly one more animal named in a one-minute verbal fluency task. In the teenagers, reading and mathematics scores were about 6% of the score range higher.
These are small effects.
But they appeared in two very different groups, tested decades apart.
And because this was an observational analysis, the researchers identified an association rather than proving that sunlight itself directly caused the changes in cognitive performance. Treating test dates as a natural experiment reduces some sources of bias, but it does not eliminate them. Sunlight was also estimated from regional weather stations, not measured on each person.
The authors discuss possible mechanisms, such as the release of nitric oxide from the skin and circadian signalling, but these remain hypotheses. According to the authors, vitamin D is unlikely to explain such short-term effects.
That distinction is important.
Your Brain Does Not Experience Light Only Through Your Eyes
When architects talk about daylight, the conversation often begins with windows, orientation, glare and illumination levels.
But biologically, light is doing more than illuminating a desk.
Specialized cells in the retina respond to environmental light and communicate information about the light-dark cycle to systems involved in regulating circadian timing. Reviews of circadian biology describe light as the main signal that keeps our internal clock aligned with the day.
This is one reason why daylight has such an important relationship with the sleep-wake cycle.
It also helps explain why the experience of being in a naturally lit environment can feel different from sitting under artificial illumination, even when both spaces appear bright enough.
The difference is not necessarily visible as a simple number on a light meter.
The brain receives information from the character, timing and composition of light as part of the environment.
Is Artificial Light a Substitute for Sunlight?
This is where things become more complicated.
Artificial lighting can obviously provide the illumination necessary to work, study and move safely through a building.
But researchers are increasingly interested in whether different lighting conditions produce different cognitive and physiological responses.
A 2026 laboratory study in Physiology & Behavior, involving 789 participants, compared bright daylight-white light (about 517 lux), neutral light (about 161 lux) and warm-white light (about 68 lux) while participants completed the Attention Network Test.
The effects were small. Warm-white light was repeatedly associated with poorer performance on alerting and executive attention, but with the best performance on orienting. And notice a detail that is easy to miss: the warm light was also much dimmer than the others, so color and brightness were changing together.
That is a useful reminder:
"Artificial light" is not one thing.
Its intensity, spectrum, color temperature, spatial distribution and timing can all change the experience.
The Architecture of Daylight Matters
This is where the subject becomes particularly interesting for anyone who designs or lives in buildings.
Imagine two rooms with the same artificial illumination level.
One has a generous window overlooking trees or an open sky.
The other has no window and depends almost entirely on artificial lighting.
A lux meter can tell you how much light reaches a particular surface.
It cannot, by itself, describe the entire experience of being in those rooms.
Recent research is beginning to examine precisely this complexity.
A 2026 study in the Journal of Building Engineering varied the proportions of daylight and artificial lighting while keeping the same illuminance on the work surface. In a small experimental study, cognitive performance declined as the share of daylight fell, with the lowest performance under fully artificial lighting. Artificial-dominant lighting also produced higher sympathetic activation, a stress-related physiological response, while daylight-dominant conditions showed more balanced autonomic regulation. Subjective comfort alone did not predict cognitive performance.
The important architectural lesson is not that every building should simply maximize daylight.
It is that the source and composition of light matter, not just the amount.
More Daylight Is Not Always Better
This is one of the places where architectural enthusiasm needs a little restraint.
A room flooded with sunlight can be beautiful.
It can also be uncomfortable.
Glare, excessive contrast, overheating and reflections on screens can make a supposedly "healthy" daylight strategy unpleasant.
Even in the research, the picture is not one-directional. A 2025 study with 41 university students in multimedia classrooms compared typical daylight with artificial lighting. Daylight was associated with smaller pupil diameters, shorter eye fixations and more localized prefrontal activation, which the authors interpret as lower visual strain and greater neural efficiency under low cognitive load. Under high cognitive load, artificial lighting provided a more stable visual environment that sustained performance. No single condition was best for every situation. A 2026 study of dynamic daylight in a university multimedia classroom likewise describes task-dependent effects on alertness and cognitive control.
Extreme brightness has limits too. In a laboratory experiment with simulated sunlight at an intensity far above what you would find in an ordinary room, prolonged exposure of the head raised core body temperature by about 1 °C and impaired motor-cognitive performance, while brief exposure did not.
That makes sense from an architectural perspective.
Good daylight is not simply abundant daylight.
It is daylight that works with the activity taking place in the room.
What Happens When You Spend Most of the Day Indoors?
This question becomes particularly relevant in modern cities.
Workplaces, apartments, schools, shopping centers and transportation systems can keep us inside for much of the day.
Sometimes that is unavoidable.
The problem is that the indoor environment can become disconnected from the changing conditions outside.
Morning becomes indistinguishable from afternoon.
Cloudy weather disappears behind artificial illumination.
The gradual transition toward evening may be invisible from the desk.
And the body receives fewer environmental cues from the natural world.
A systematic review of how indoor environmental quality affects cognitive functions found that poor conditions are often, but not always, associated with reduced cognition, that the effect of a given factor differs from one cognitive function to another, and that the literature contains extensive inconsistencies.
In other words, there is still a lot we do not know.
But the direction of research is becoming increasingly clear: the indoor environment is not psychologically neutral.
Your Window May Be Doing More Than Providing a View
From an architectural perspective, I think this is one of the most interesting consequences of the research.
We often treat a window as an opening in a wall.
Functionally, it provides daylight, ventilation or a view.
Experientially, it can provide something else: a connection to changing environmental conditions.
The sky changes.
Clouds move.
Trees move in the wind.
The intensity of daylight shifts.
The color of the room changes throughout the day.
These variations give the interior a temporal dimension.
A room without visual access to these changes can feel remarkably static.
That does not mean every room needs enormous glass walls. In some situations, excessive glazing creates glare, heat gain or privacy problems.
The architectural challenge is more subtle:
How can a building provide useful contact with daylight without sacrificing visual comfort?
Could Daylight Help You Stay More Alert?
There is evidence suggesting that light can influence alertness and certain aspects of attention.
But it would be too strong to say:
"Sunlight makes you smarter."
The research does not support such a simple conclusion.
The 2026 sunlight study found associations with several cognitive measures, particularly under lower solar-radiation conditions. The laboratory lighting study found small effects that differed across components of attention. And the classroom research suggests that responses to daylight can depend on the task.
So the more accurate picture is this:
Light is one environmental factor that interacts with the brain, body, behavior and context.
That is already fascinating enough.
What Can You Change at Home?
You do not need to redesign your entire house to think differently about daylight.
Start by observing your environment.
Where does the strongest natural light enter your home?
Which rooms receive morning light?
Which spaces become dark during the day?
Where do you spend most of your time?
And perhaps most importantly:
Do you spend your entire day in the same lighting conditions?
If your workspace is next to a window, for example, you may have access to changing daylight throughout the day without doing anything special.
If the room is poorly positioned, however, simply having a window may not be enough.
Furniture placement, curtains, glazing, neighboring buildings, orientation and exterior obstructions can all change how daylight actually reaches the interior.
This is where architecture becomes practical.
The goal is not to "hack" your brain.
It is to create an environment that gives the body more useful information about the world outside.
The Best Daylight Strategy Is Not the Brightest Room
One of the biggest mistakes in conversations about healthy buildings is turning a complex relationship into a single rule.
More light.
More plants.
More openness.
More nature.
More is not always better.
Architecture is about relationships.
A bright room can become uncomfortable if glare makes it difficult to work.
A huge window can become a thermal problem.
A dark room can feel oppressive, but a dim corner can also be exactly what someone wants for rest.
The question is not:
"How much daylight should this room have?"
It is:
"How should daylight behave in this room, for the people using it, throughout the day?"
That is a much more architectural question.
What This Means for the Way We Design Homes
For me, the most interesting lesson from the recent research is that daylight should not be treated merely as an energy or illumination problem.
It is part of the experience of inhabiting a place.
A well-designed home can allow you to notice morning, afternoon and evening without needing a clock.
It can give you brighter areas for concentration and quieter areas for rest.
It can frame the sky without forcing you to sit directly in glare.
It can let daylight change gradually across surfaces rather than flooding everything with uniform brightness.
These decisions may seem small on a floor plan.
But they change the experience of the person living there.
Interestingly, the authors of the sunlight study close with an architectural suggestion of their own: designing buildings and built environments that encourage sunlight exposure and outdoor activity, particularly in low-light seasons, could be a complementary strategy to support cognitive performance.
And that is one of the reasons I find the relationship between architecture and human behavior so compelling.
We don't simply live inside buildings. We experience time, light and our surroundings through them.
Final Thoughts
The newest research does not show that a lack of sunlight automatically harms your brain.
It shows something more useful.
Our relationship with natural light is worth paying attention to.
The September 2026 study found associations between short-term solar exposure and several measures of cognitive performance, particularly under relatively low-light conditions. Other 2026 experiments suggest that the composition, color and spatial distribution of indoor lighting can also influence alertness, stress and cognitive performance, although the effects are often small and depend on the task.
There is still much to understand about causality, individual differences and the ideal amount and timing of exposure.
But one idea is becoming increasingly difficult to ignore:
The light around you is part of the environment your brain lives in.
And sometimes, the simplest architectural intervention may begin with something we have had since the beginning of human history:
Letting the daylight in.
Educational Disclaimer
This article is provided for educational and informational purposes only. It is not medical advice, diagnosis, or treatment. The research discussed describes scientific findings and associations and should not be interpreted as a recommendation for a specific health intervention.
References
- Stevenson, A., & Dibben, C. (2026). Acute lack of sunlight exposure is associated with poorer cognitive test performance: evidence from two national cohorts in the United Kingdom. Photochemical & Photobiological Sciences. Read the article (DOI) | Open-access page
- Dijk, D.-J., & Archer, S. N. (2009). Light, sleep, and circadian rhythms: together again. PLoS Biology, 7(6), e1000145. Read the article (DOI)
- Effects of human-centric lighting on performance in the attentional network test (ANT) and on perceived stress. (2026). Physiology & Behavior, 310, 115296. Read the article (DOI) | PubMed
- Rehman, S., Chani, P. S., & Elangovan, R. (2026). Neuro-psychophysiological and cognitive impacts of indoor lighting compositions. Journal of Building Engineering, 128, 116450. Read the article (DOI)
- Lighting effects on visual and cognitive adaptation in multimedia classrooms: a multimodal neurophysiological study. (2025). Building and Environment. Read the article (ScienceDirect)
- Task-dependent effects of dynamic daylight on alertness and cognitive control in a university multimedia classroom. (2026). Building and Environment. Read the article (DOI)
- Piil, J. F., et al. (2020). Direct exposure of the head to solar heat radiation impairs motor-cognitive performance. Scientific Reports, 10, 7812. Read the article (DOI) | Full text (PMC)
- Wang, C., et al. How indoor environmental quality affects occupants' cognitive functions: a systematic review. Read the record (PolyU repository)
- The impact of human-centric lighting parameters on older adults' perception and cognitive performance. University of Oregon thesis. Read the thesis (Scholars' Bank)
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