Each additional hour of daytime sunlight exposure was associated with an increase of 10.67 minutes in total sleep time the following night and a decrease in light sleep percentage, while evening smartphone use before bedtime was linked to increased sleep onset latency, but no associations were found between artificial light exposure and sleep outcomes.
Key Findings
Results
Each additional hour of daytime sunlight exposure was associated with significantly longer total sleep time the following night.
Each additional hour of daytime sunlight exposure was associated with an increase of 10.67 minutes in TST (95% CI 0.6–20.7 minutes).
Sunlight exposure was defined as the number of hours above 1000 lux during daytime.
Linear mixed-effects models with a random intercept at the individual level were used, adjusting for step count and other individual covariates.
The study involved 21 participants monitored over 7 consecutive days.
Results
Each additional hour of daytime sunlight exposure was associated with a small but statistically significant decrease in light sleep (N1) percentage.
Each additional hour of daytime sunlight exposure was associated with a 0.3 percentage-point decrease in N1 percentage (95% CI -0.6 to -0.0).
Light sleep (N1) represented 6.6% (SD 2.1%) of total sleep time on average across participants.
The decrease in N1 suggests an improvement in sleep architecture quality associated with sunlight exposure.
Sleep staging was derived from the Dreem wearable electroencephalography device.
Results
Each additional minute of smartphone use before bedtime was associated with increased sleep onset latency.
Each minute of smartphone use before bedtime was linked to an increase in SOL of 0.2 minutes (95% CI 0.0–0.4 minutes).
Smartphone use was quantified as duration accumulated in the 2 hours preceding sleep onset.
Average sleep onset latency across participants was 17.6 minutes (SD 18 minutes).
Smartphone usage was recorded via a dedicated mobile app.
Results
No statistically significant associations were found between evening artificial light exposure and any sleep outcomes.
Artificial light exposure before bedtime was quantified as duration of exposure accumulated in the 2 hours preceding sleep onset.
Light exposure was measured using HOBO data loggers worn by participants.
The null finding for artificial light contrasts with the significant association found for smartphone use, suggesting digital engagement (rather than light per se) may be the key disruptor.
Sleep outcomes examined included TST, SOL, N1 percentage, and N3 percentage.
Results
The study characterized average sleep architecture across the 21 participants monitored with wearable EEG over 7 days.
Average total sleep time was 420 minutes (SD 85 minutes).
Average sleep onset latency was 17.6 minutes (SD 18 minutes).
Light sleep (N1) represented 6.6% (SD 2.1%) of sleep.
Deep sleep (N3) accounted for 20.1% (SD 7.6%) of sleep.
Participants were recruited from the Jerusalem metropolitan area and monitored continuously using the Dreem wearable EEG for sleep staging.
Methods
The study demonstrated the feasibility of integrating multiple wearable and environmental sensors to measure sleep architecture and its behavioral and environmental correlates in naturalistic, real-world settings.
Sensors included the Dreem wearable EEG for sleep staging, HOBO data loggers for light exposure, wGT3X+ triaxial accelerometer for physical activity, and a dedicated mobile app for smartphone usage.
21 participants were monitored continuously over 7 consecutive days.
Day-to-day associations were estimated, capturing within-person variability across the week.
The study is described as a 7-day sensor-based observational study in naturalistic settings.
What This Means
This research suggests that getting more sunlight during the day is associated with better sleep the following night. Specifically, each additional hour of bright sunlight (above 1000 lux) was linked to about 10 more minutes of total sleep and a slight reduction in the lightest stage of sleep, suggesting that daytime sunlight helps align the body's internal clock in ways that improve nighttime sleep quality. The study tracked 21 people in Jerusalem for a week using wearable brain activity monitors, light sensors, activity trackers, and smartphone logging apps to capture real-world sleep and light exposure simultaneously.
The research also found that using a smartphone in the two hours before bed was associated with taking longer to fall asleep — roughly an extra 0.2 minutes of delay per minute of phone use. Interestingly, general artificial light exposure in the evening (measured by light sensors) was not associated with worse sleep, suggesting it may be the mental engagement or stimulation from smartphone use specifically — rather than the light from screens alone — that disrupts sleep onset.
This study matters because it provides real-world, sensor-based evidence collected over multiple days rather than in a lab, making the findings more applicable to everyday life. The results suggest that prioritizing outdoor time during the day and reducing smartphone use in the evening may support healthier sleep patterns, particularly in terms of sleep duration and how quickly people fall asleep.
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Montanari A, Wang L, Birenboim A, Chaix B. (2026). The Impact of Sunlight and Artificial Light at Night on Sleep Stages: Evidence From a 7-Day Sensor-Based Observational Study.. JMIR mHealth and uHealth. https://doi.org/10.2196/75898