How Everyday Light Exposure Relates to Attention and Reaction Speed, a New Study Finds
Light surrounds us every day, but its influence on how we think and respond outside the laboratory has been hard to measure. A new peer-reviewed study tracked real-world light exposure and cognitive performance in adults as they went about their normal routines. Using wearable sensors and smartphone-based tasks, researchers examined how recent and habitual light exposure relate to attention, reaction speed, and subjective sleepiness. The results offer a detailed look at how everyday lighting environments are associated with cognitive function.
Note: This article is intended for general information and educational purposes. It summarizes scientific research in accessible language for a broad audience and is not an official scientific press release.
Light is one of the most constant features of human environments, yet its effects on cognition have mostly been studied under tightly controlled laboratory conditions. While such studies have shown that light can influence alertness and mental performance, far less is known about how these effects translate into everyday life, where light exposure varies continuously throughout the day.
A new peer-reviewed study published in Communications Psychology on December 16, 2025, set out to address this gap by examining real-world light exposure and cognitive performance during normal daily routines. The research was led by Altug Didikoglu and conducted by an international, multidisciplinary team of researchers: Altug Didikoglu, Tom Woelders, Lucien Bickerstaff, Navid Mohammadian, Sheena Johnson, Martie van Tongeren, Alexander J. Casson, Timothy M. Brown, and Robert J. Lucas.
The authors are affiliated with the Department of Neuroscience at Izmir Institute of Technology (Turkey); multiple departments at the University of Manchester (United Kingdom), including the Centre for Biological Timing, the School of Biological Sciences, the School of Medical Sciences, the School of Engineering, the Alliance Manchester Business School, and the Thomas Ashton Institute; as well as the Max Planck Institute for Biological Cybernetics (Germany) and the TUM School of Medicine and Health, Technical University of Munich (Germany).
According to the authors, the study examined whether real-world light exposure is associated with cognitive performance, including attention, working memory, visual search, and subjective sleepiness, during normal daily life. To do so, the researchers combined continuous personal light monitoring with repeated cognitive testing over seven days.
What the Researchers Investigated
The researchers focused on a simple but unresolved question: how does everyday light exposure relate to cognitive performance outside laboratory settings?
Previous research has demonstrated that light can modulate cognitive function in controlled environments, often using carefully timed light exposure and standardized tasks. However, the authors note that real-world light exposure is dynamic, shaped by indoor lighting, outdoor daylight, work schedules, and personal routines.
In this study, the researchers investigated whether both recent light exposure (over minutes to hours) and habitual light exposure patterns (across days) are associated with cognitive outcomes. These outcomes included subjective sleepiness, sustained attention, working memory, and visual search performance.
The study examined adults living typical daily lives, without major circadian challenges such as night shift work or recent jet lag. Participants were instructed not to change their routines, allowing researchers to observe natural variations in light exposure and cognition.
How the Study Was Conducted
The study took place in Manchester, United Kingdom, between July 2022 and August 2023. Sixty adults initially enrolled, with 58 participants included in the final analyses after exclusions for incomplete data or protocol noncompliance. The final sample included equal numbers of men and women.
Participants and daily life setting
Participants were adults aged eighteen and older who were employed either full-time or part-time. Individuals with diagnosed sleep disorders or recent intercontinental travel were excluded. Importantly, participants continued their normal daily routines throughout the study.
Measuring light exposure
Participants wore a wrist-mounted light sensor that continuously measured melanopic equivalent daylight illuminance. This measure captures light exposure relevant to non-visual biological responses, including those mediated by melanopsin-containing retinal cells.
The device recorded light exposure every thirty seconds throughout the day. Participants removed it before bedtime and placed it in a consistent location near eye level overnight.
Measuring cognitive performance
Cognitive performance and subjective sleepiness were assessed using a smartphone-based platform delivering repeated cognitive tasks and self-reports. Participants completed repeated sessions during the day, including:
- A Psychomotor Vigilance Task measuring sustained attention and reaction time
- A three-back working memory task, which required participants to remember and compare items presented moments earlier
- A visual search task
- A subjective sleepiness rating scale
Participants completed these assessments multiple times per day, rather than at fixed hours, allowing the researchers to capture cognitive performance across different lighting conditions and times of day.
Additional laboratory assessments
A subgroup of 41 participants attended an optional laboratory session. These sessions measured pupil responses and perceptual sensitivity to light, focusing on melanopsin-related responses. The authors note that these laboratory measures were analyzed separately and compared with real-world cognitive outcomes.
What Makes This Study New
The authors highlight several aspects that distinguish this research from previous work.
First, the study focused primarily on real-world conditions, with participants continuing their normal routines rather than being exposed to controlled lighting schedules. This allowed the researchers to observe how natural variations in light exposure relate to cognition.
Second, the study combined continuous personal light monitoring with repeated cognitive testing over an entire week. According to the authors, this approach made it possible to examine both short-term and longer-term associations between light exposure and cognitive performance.
Finally, the researchers analyzed not only light intensity, but also patterns of light exposure, including stability and fragmentation across days. This broader view of light exposure is rarely captured in laboratory studies.
Key Findings From the Study
The study identified several statistically significant associations between light exposure and cognitive measures.
1. Recent light exposure and subjective sleepiness. Recent light exposure was associated with lower subjective sleepiness, independent of time of day. According to the authors, higher light exposure in the preceding minutes to hours was linked to reduced sleepiness scores.
2. Light exposure and reaction time. Recent light exposure was also associated with faster reaction times in both the psychomotor vigilance task and the working memory task. The authors report that reaction times were shorter following brighter light exposure compared with dimmer conditions.
3. Daytime light patterns and visual search performance. The study further found that higher daytime light exposure and less fragmented daily light patterns were associated with better performance in visual search tasks, including fewer errors and greater task efficiency.
4. Light exposure compared with time of day. Importantly, the authors report that time of day and time awake showed weaker associations with cognitive performance than light exposure. In their analyses, light exposure demonstrated stronger associations with several cognitive outcomes than clock time.
5. Individual differences in light–cognition relationships. The researchers also observed substantial inter-individual variability. While many participants showed associations between light exposure and cognitive measures, the strength and direction of these associations varied across individuals.
Authors’ Conclusions
The authors conclude that both recent and habitual light exposure are meaningfully associated with aspects of cognitive performance in everyday life.
They suggest that brighter light exposure is associated with lower subjective sleepiness and faster reaction times in attention and working memory tasks. The authors interpret these findings within existing research on melanopsin-mediated retinal pathways, which are known to influence alertness and circadian regulation.
The study is explicitly described as correlational, and the authors emphasize that it does not establish causality. They also note limitations related to sample size and participant characteristics, including the focus on adults without major circadian disruption.
The authors recommend that future research examine broader populations and further explore individual differences in sensitivity to light.
Understanding the Broader Context
These findings contribute to a growing scientific literature examining how environmental factors relate to cognitive function outside laboratory settings.
By combining wearable sensors with smartphone-based cognitive testing, the study adds descriptive evidence on how everyday light exposure patterns relate to attention, reaction speed, and subjective sleepiness. The authors note that this approach may help bridge the gap between laboratory research and real-world conditions.
Conclusion
This study provides detailed observational evidence linking real-world light exposure to multiple aspects of cognitive performance during daily life. By tracking light exposure and cognition continuously over a week, the researchers were able to examine how both short-term and habitual lighting environments are associated with attention, reaction speed, and subjective sleepiness.
As the authors emphasize, further research is needed to clarify mechanisms, individual differences, and the extent to which these associations generalize to other populations. The findings add to ongoing research on how light interacts with brain function beyond controlled experimental settings.
The information in this article is provided for informational purposes only and is not medical advice. For medical advice, please consult your doctor.
Reference
Didikoglu, A., Woelders, T., Bickerstaff, L., Mohammadian, N., Johnson, S., van Tongeren, M., Casson, A. J., Brown, T. M., & Lucas, R. J. (2026). Relationships between light exposure and aspects of cognitive function in everyday life. Communications Psychology, 4, Article 5.
https://doi.org/10.1038/s44271-025-00373-9
