Outdoor nighttime light exposure was associated with slightly longer light sleep duration (1.22 min per standard deviation increase) and a non-linear negative pattern for deep sleep at higher exposure levels, with stronger associations in elderly, lower BMI, non-drinker, smoker, and non-middle-income subgroups.
Key Findings
Results
One standard deviation increase in outdoor nighttime light (NTL) exposure was associated with a statistically significant increase in light sleep duration.
One standard deviation of NTL exposure was 5.20 W·cm²·SR⁻¹
The association was statistically significant based on the confidence interval not crossing zero
Mixed-effects regression models were used, adjusting for demographic, behavioral, and environmental covariates
Results
No overall linear association was found between outdoor NTL exposure and total sleep duration or deep sleep duration.
The linear association with total sleep duration was described as 'not evident'
The linear association with deep sleep duration was also described as 'not evident'
This finding suggests NTL selectively affects sleep stage composition rather than overall sleep length
Results
Restricted cubic spline analyses revealed a non-linear pattern for deep sleep, with a modest decline at higher NTL levels.
The non-linear relationship specifically showed a decline in deep sleep at higher NTL exposure levels
The pattern was described as 'modest'
This non-linearity was not captured by the primary linear models, requiring spline analysis to detect
Results
Subgroup analyses revealed stronger NTL-sleep associations in elderly participants and those with lower BMI.
Elderly participants showed stronger associations between NTL exposure and sleep metrics
Participants with lower BMI demonstrated stronger associations compared to higher BMI participants
These subgroup differences suggest differential vulnerability to outdoor light exposure
Results
Positive associations between NTL exposure and sleep outcomes were found in non-drinkers, smokers, and participants from non-middle-income areas.
Non-drinkers showed positive associations with NTL exposure and sleep parameters
Smokers showed positive associations with NTL exposure and sleep parameters
Participants from non-middle-income areas showed positive associations
These subgroup findings suggest behavioral and socioeconomic factors moderate the NTL-sleep relationship
Methods
The study used a panel design with objective sleep data collected from 4,690 participants over two years using consumer-grade wearable devices.
Sleep metrics were collected from 4,690 participants between 2017 and 2019
Zepp Health smart bracelets were used for objective sleep measurement
Outdoor NTL exposure data were obtained from NASA's Black Marble product
NTL exposure was categorized into tertiles for analysis
Mixed-effects regression models were employed to account for the panel structure of the data
What This Means
This research suggests that living in areas with brighter outdoor nighttime artificial lighting is associated with small but measurable changes in how people sleep. Using wrist-worn fitness trackers from nearly 4,700 people in China observed over two years, researchers found that higher outdoor light pollution was linked to slightly more time spent in light (shallower) sleep — about 1.22 minutes more per standard deviation increase in light exposure. However, this brighter outdoor lighting did not appear to meaningfully change total sleep time in a straightforward linear way.
The study also found that at the highest levels of outdoor light exposure, there was a modest decline in deep sleep — the most restorative stage of sleep — though this pattern only emerged when using more flexible statistical methods that can detect curved rather than straight-line relationships. Certain groups appeared more sensitive to these effects, including older adults, people with lower body weight, non-drinkers, smokers, and people living outside middle-income areas.
This research matters because it uses real-world, objectively measured sleep data rather than self-reports, and links it to satellite-based measurements of actual outdoor light levels rather than self-reported exposure. The findings suggest that urban lighting policies could have meaningful consequences for public health, particularly for vulnerable groups, and that guidelines balancing nighttime safety with sleep health may be warranted. The effects observed are modest, but given how widespread light pollution is globally, even small average changes could have population-level significance.
Yang H, Liu J, Chen Y, Su M, Thepanondh S, Zhou P, et al.. (2026). Outdoor night light exposure and sleep structure, a panel study using consumer-grade wearables.. BMC public health. https://doi.org/10.1186/s12889-025-26132-3