Summary:
A new study finds that exposure to light at night is strongly linked to objectively measured sleep disruption in outpatients with schizophrenia. Participants whose bedrooms were brighter at night slept nearly an hour less on average. Even relatively low levels of nocturnal illumination were associated with worse sleep efficiency and more time awake during the night, identifying a straightforward, nonpharmacological target for improving sleep hygiene in this population.
Key Facts:
- Substantial sleep loss: Participants in the brightest nighttime light group averaged 55.6 minutes less total sleep per night, displayed a 10% lower sleep efficiency, and experienced 31 additional minutes awake after initially falling asleep compared with those in the darkest group.
- Low disruption threshold: Significant sleep disturbances were observed at modest illumination levels—median nighttime light was 1.4 lux recorded at the wrist and 4.1 lux at the bedside.
- Objective measures reveal hidden effects: The association between nocturnal light and sleep fragmentation appeared in actigraphy data but not in self-reported Pittsburgh Sleep Quality Index (PSQI) scores, suggesting many patients may not be aware of light-driven sleep disruption.
Source: Fujita Health University
Bedroom Light and Sleep Disturbance in Schizophrenia
Sleep problems are common in people with schizophrenia and can worsen cognitive performance, psychiatric symptoms, and daily functioning. While artificial light at night has been shown to disrupt circadian rhythms and sleep in the general population, its specific effects on sleep patterns in schizophrenia have not been thoroughly explored using both objective and subjective measures—until now.
Researchers at Fujita Health University conducted a cross-sectional analysis demonstrating that nighttime light exposure correlates with marked, measurable sleep fragmentation among adult outpatients with schizophrenia. The results, accepted for publication in Psychiatry Research, indicate that even relatively low bedroom illumination is linked to detectable declines in sleep quality.
The LENS Study: Tracking Real-World Light and Rest
The analysis included 225 adult outpatients enrolled in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. To capture typical environmental exposure, participants were monitored continuously for seven days without altering their usual routines.
Researchers combined several concurrent measures to assess sleep and light exposure:
- Wrist actigraphy: Devices worn continuously recorded movement, sleep-wake patterns, and personal light exposure.
- Bedside photometry: Portable light sensors placed next to each bed independently measured ambient nocturnal illumination and exposure to blue wavelengths.
- Sleep diaries and questionnaires: Daily sleep diaries tracked bed and rise times, and participants completed the standardized Pittsburgh Sleep Quality Index to report perceived sleep quality.
Although nighttime illumination was modest (median 1.4 lux at the wrist and 4.1 lux at the bedside), differences in sleep quality between darker and lighter sleeping environments were pronounced.
Measurable Reductions in Sleep Architecture
The researchers adjusted for a broad set of potential confounders—age, sex, body mass index, smoking, daytime light exposure, seasonal day length, sleep timing, baseline psychiatric symptoms, and medications including antipsychotics and sedatives—and the associations persisted.
Participants in the highest nighttime light quartile experienced a 10% reduction in sleep efficiency, delayed sleep onset, 31 more minutes of wakefulness after sleep onset (WASO), and 55.6 fewer minutes of total sleep per night compared with those in the lowest quartile. Nighttime exposure to blue wavelengths produced similar patterns of disruption.
“Even relatively low levels of nighttime light may be linked to measurable sleep disruption in people with schizophrenia,” said lead student author Ryota Miyake.
The Hidden Sleep Gap: Objective vs. Subjective Awareness
Notably, the objective actigraphy data showed clear biological sleep loss, while PSQI scores—reflecting subjective sleep quality over the previous month—did not demonstrate a significant association with nighttime light. This divergence may reflect differences in measurement windows, but it also suggests that patients may experience micro-arousals and fragmented sleep without recognizing that their bedroom lighting contributes to the problem.
A Modifiable, Nonpharmacological Target
The authors emphasize that this cross-sectional analysis establishes correlation rather than causation and that longitudinal intervention studies are needed to confirm causal effects. Still, ambient light is an accessible and low-cost factor that can be modified without medication.
Practical steps—such as turning off electronic indicator lights, using blackout curtains, dimming hallway lights, or reducing blue-light exposure in bedrooms and psychiatric residential settings—could be integrated into sleep hygiene routines. If future randomized studies corroborate these findings, reducing nighttime light exposure could improve nighttime sleep, enhance daytime functioning, reduce reliance on sedative medications, and raise overall quality of life for people with schizophrenia.
Funding information
This study was supported by Scientific Research funding from JSPS KAKENHI (grant number: 24K10721) and the Takeda Science Foundation.
Editorial Notes:
- This piece was edited by a Neuroscience News editor.
- The journal article was reviewed in full by staff.
- Additional context was added by editorial staff.
About this Genetics and Neurology Research:
- Media contact: Hisatsugu Koshimizu
- Source: Fujita Health University
- Image credit: Image generated for Neuroscience News
- Original research (open access): Psychiatry Research (October, 2026). Title: “Light exposure at night and subjective and objective sleep parameters in patients with schizophrenia: A cross-sectional analysis of the LENS study.” Authors: Ryota Miyake, Yuichi Esaki, Rina Taniguchi, Kenji Obayashi, Keigo Saeki, Soji Tsuboi, Kiyoshi Fujita, Nakao Iwata, and Tsuyoshi Kitajima.
- DOI: 10.1016/j.psychres.2026.117302
Abstract
Light exposure at night and subjective and objective sleep parameters in patients with schizophrenia: A cross-sectional analysis of the LENS study
Introduction
Nighttime light exposure has been associated with sleep problems in the general population. This study examined the relationship between nighttime illumination and both subjective and objective sleep measures in patients with schizophrenia, a group with high rates of sleep disturbance.
Methods
This cross-sectional analysis enrolled 225 outpatients with schizophrenia from the LENS study. Subjective sleep quality was measured using the Pittsburgh Sleep Quality Index, while objective sleep patterns were recorded continuously for seven days with wrist actigraphy. Nighttime light exposure—from bedtime to rising—was measured by the actigraph and by a portable photometer placed at the bedside.
Results
Median nighttime illuminance was 1.4 lux (interquartile range [IQR], 0.5–4.5) by actigraphy and 4.1 lux (IQR, 1.0–15.4) by photometer. After adjusting for multiple confounders, participants in the highest quartile of nighttime illuminance (by actigraphy) showed significantly lower sleep efficiency (by 10.0%), reduced total sleep time (by 55.6 minutes), longer sleep onset (0.2 log minutes), and increased wake after sleep onset (by 31.0 minutes) compared with those in the lowest quartile. Similar associations were seen using photometer measurements. Subjective sleep measures on the PSQI did not show a significant link to nighttime light exposure.
Conclusions
Nighttime light exposure was significantly associated with objective measures of sleep disturbance in patients with schizophrenia. Further longitudinal and interventional research is needed to clarify causality and to test whether reducing nocturnal light can improve sleep and clinical outcomes.