Summary:
A new study reveals that nighttime light exposure is strongly associated with objective sleep disruption in outpatients with schizophrenia, resulting in nearly an hour less total sleep per night. Even at low lux levels, higher nocturnal illumination corresponded to reduced sleep efficiency and extended nighttime wakefulness, presenting a simple, nonpharmacological target for sleep hygiene intervention.
Key Facts:
- Substantial Sleep Deficit: Patients in the highest nighttime light group lost an average of 55.6 minutes of total sleep, had 10% lower sleep efficiency, and spent 31 more minutes awake after initially falling asleep compared to those in the lowest light group.
- Low Threshold for Disruption: Sleep impairments occurred at relatively low illumination levels, with median nighttime illuminance recorded at just 1.4 lux on wrist actigraphy and 4.1 lux on bedside photometers.
- Objective vs. Subjective Discrepancy: The detrimental impact of nocturnal light was identified exclusively through objective actigraphy, not the self-reported Pittsburgh Sleep Quality Index, suggesting many patients do not consciously recognize their light-induced sleep fragmentation.
Source: Fujita Health University
Bedroom Light and Sleep Disturbance in Schizophrenia
Sleep disturbances are pervasive among individuals diagnosed with schizophrenia, frequently exacerbating cognitive deficits, psychiatric symptom severity, and overall functional outcomes. While artificial nighttime light is well known to impair circadian entrainment and sleep architecture in the general population, its precise neurobiological footprint on sleep in schizophrenia has remained largely under-investigated through combined objective and subjective methodologies.
Now, a research team led by Fujita Health University in Japan has provided the first evidence that nighttime light exposure is associated with marked, measurable sleep deficits in adult outpatients with schizophrenia.
The study, scheduled for publication in Psychiatry Research, demonstrates that even modest bedroom illuminance tracks with severe sleep fragmentation.
The LENS Study: Tracking Real-World Illumination and Rest
The investigators analyzed 225 adult outpatients participating in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. To capture real-world environmental exposure without disrupting normal routines, participants were monitored continuously for seven days.
The evaluation combined multiple concurrent metrics:
- Wrist Actigraphy: Worn 24/7 to continuously record motor activity, sleep cycles, and individual light exposure.
- Bedside Photometry: Portable light sensors placed beside each patient’s bed to independently capture ambient nocturnal illumination and blue-light exposure.
- Diaries & Questionnaires: Daily sleep diaries logging bedtime and rising times, paired with the standardized Pittsburgh Sleep Quality Index (PSQI) assessing subjective sleep quality.
The recorded nighttime illuminance was modest, a median of 1.4 lux via wrist actigraphy and 4.1 lux by bedside photometers. Yet, despite these low absolute values, researchers identified steep differences in sleep quality between light-exposed and dark environments.
Measurable Reductions in Sleep Architecture
After adjusting for an extensive array of potential confounders, including age, sex, BMI, smoking status, daytime light levels, natural day length, sleep timing, baseline psychiatric symptoms, and antipsychotic or sedative medications, the association remained robust.
Patients in the highest nighttime light tier showed a 10% reduction in sleep efficiency, took longer to fall asleep (delayed sleep onset), endured 31 additional minutes of wakefulness after sleep onset (WASO), and accumulated 55.6 fewer minutes of total sleep duration per night compared to those sleeping in darker rooms. Exposure to blue wavelengths at night produced similarly pronounced sleep disruptions.
“Our findings suggest that 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
Intriguingly, while actigraphy verified substantial biological sleep loss, the self-reported PSQI scores showed no statistically significant link to nighttime light.
The authors note that this divergence could stem from the different assessment windows, PSQI reflects retrospective perception over a full month, whereas actigraphy was measured prospectively over seven days. However, it also highlights an important clinical insight: individuals with schizophrenia may suffer from pronounced micro-arousals and fragmented rest without consciously realizing that their bedroom environment is actively degrading their sleep.
A Modifiable, Nonpharmacological Target
The authors emphasize that the study’s cross-sectional design demonstrates correlation rather than direct causation, calling for prospective randomized trials to establish definitive causal mechanisms.
Nonetheless, ambient light represents an accessible, zero-cost environmental factor. Simple modifications, such as eliminating electronic indicator lights, turning off hallway bulbs, or introducing blackout curtains in private bedrooms and psychiatric residential facilities, could form a pillar of clinical sleep hygiene.
“Optimizing the nighttime light environment could become an important part of sleep hygiene if future longitudinal and intervention studies confirm these findings,” Miyake noted. If confirmed, reducing nighttime light exposure could improve daytime functioning, lower reliance on supplemental sedative medications, and enhance quality of life in schizophrenia care.
Funding information
This work was supported by Scientific Research funding from JSPS KAKENHI (grant number: 24K10721) and Takeda Science Foundation.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this Genetics and Neurology Research:
- Media Contact: Hisatsugu Koshimizu
- Source: Fujita Health University
- Image Credit: Image generated for Neuroscience News
- Original Research is Open Access: Psychiatry Research (October, 2026). “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 reported to be associated with sleep problems in the general population. This study aimed to investigate the association between nighttime light exposure and both subjective and objective sleep parameters in patients with schizophrenia, who often experience sleep disturbances.
Methods
This cross-sectional study included 225 outpatients with schizophrenia who participated in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. Sleep was subjectively measured using the Pittsburgh Sleep Quality Index and objectively evaluated over 7 consecutive days using a wrist-worn actigraphy, respectively. Nighttime light exposure (from bedtime to rising time) was measured using an actigraphy and a portable photometer placed at the patient’s bedside.
Results
The median nighttime illuminance measured using the actigraphy and photometer was 1.4 lux (interquartile range [IQR], 0.5–4.5) and 4.1 lux (IQR, 1.0–15.4), respectively. After adjusting for potential confounding factors, the highest quartile of nighttime illuminance measured using the actigraphy was significantly associated with lower sleep efficiency by 10.0%, lower total sleep time by 55.6 minutes, longer sleep onset time by 0.2 log minutes, and longer wake after sleep onset by 31.0 minutes, than the lowest quartile. Similarly, an association was observed between nighttime illuminance measured using the photometer and each sleep parameter. Whereas, subjective sleep parameter was not significantly associated with nighttime light exposure.
Conclusions
Nighttime light exposure was significantly associated with objective sleep parameters in patients with schizophrenia. Further longitudinal studies are needed to clarify this association.
