Sleep problems are common in people with schizophrenia and can worsen quality of life, psychiatric symptoms, cognition, and daily functioning. Nighttime light is known to interfere with normal sleep and circadian rhythms in the general population, but its relationship with sleep in schizophrenia had not been examined using both objective and subjective measures. The new study provides the first evidence that greater nighttime light exposure is associated with poorer objectively measured sleep in outpatients with schizophrenia. The authors emphasize that the findings should be viewed as an association rather than proof of cause and effect, pending prospective intervention studies.
The researchers analyzed 225 adult outpatients with schizophrenia who took part in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. Participants wore a wrist actigraphy device continuously for seven days to measure sleep and light exposure. A portable photometer placed beside the bed independently measured ambient nighttime illuminance, while a sleep diary recorded bedtime and rising time. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index. The findings were made available online on June 23, 2026, and will be published in Volume 364 of the journal Psychiatry Research on October 01, 2026.
The study was led by Dr. Yuichi Esaki and Mr. Ryota Miyake, a student, together with Dr. Nakao Iwata and Dr. Tsuyoshi Kitajima from the Department of Psychiatry, Fujita Health University School of Medicine, Aichi, Japan, and Dr. Kiyoshi Fujita from the Department of Psychiatry, Okehazama Hospital, Aichi, Japan. Median nighttime illuminance was 1.4 lux by actigraphy and 4.1 lux by photometer. After accounting for factors including age, sex, smoking, body mass index, psychiatric symptoms, daytime light, sleep timing, day length, and medications, people in the highest nighttime-light group had 10% lower sleep efficiency, 55.6 minutes less total sleep, longer sleep onset, and 31 minutes more wakefulness after sleep onset than those in the lowest-light group. Higher blue-light exposure showed similar associations.
"Our findings suggest that even relatively low levels of nighttime light may be linked to measurable sleep disruption in people with schizophrenia," said Mr. Miyake.
Importantly, the relationship was seen in objective sleep measures but not in the Pittsburgh Sleep Quality Index. This difference may indicate that some patients experience poorer sleep without fully recognizing it, or may reflect the different measurement periods: Subjective sleep was assessed over the previous month, whereas actigraphy and light exposure were measured prospectively for seven days.
The findings point to a potentially simple way to support sleep management. Reducing unnecessary light in bedrooms could provide a low-cost, nonpharmacological approach alongside existing treatment, although the cross-sectional design means the study cannot show that nighttime light causes poor sleep.
"Optimizing the nighttime light environment could become an important part of sleep hygiene if future longitudinal and intervention studies confirm these findings," said Mr. Miyake.
Such research could eventually guide lighting practices in homes, hospitals, and residential facilities, potentially supporting healthier sleep and reducing the need for additional sedating medication. Future trials could test whether darker bedrooms improve sleep, symptoms, daytime functioning, and overall quality of life in this population. Overall, the study highlights nighttime light as a modifiable environmental factor that deserves greater attention in sleep care for people with schizophrenia.
Reference
Title of original paper: Light exposure at night and subjective and objective sleep parameters in patients with schizophrenia: A cross-sectional analysis of the LENS study
Journal: Psychiatry Research
DOI: https://doi.org/10.1016/j.psychres.2026.117302
About Fujita Health University
Fujita Health University (FHU) is a private medical university located in Aichi, Japan. Established in 1964, it houses one of the largest university hospitals in Japan. It's 900 member faculty provides diverse learning and research opportunities to medical students worldwide. Guided by its founding philosophy of "Our creativity for the people" Fujita Health University believes that it's students can shape the future through creativity and innovation. FHU has earned global recognition, ranking eighth among all universities and second among private universities in Japan in the 2020 Times Higher Education (THE) World University Rankings. The university ranked fourth worldwide in the 2024 THE University Impact Rankings for contributions to the "Good Health and Well-being" SDG (Sustainable Development Goals) of the United Nations (UN). In June 2021, the university made history as the first Japanese institution to host the THE Asia Universities Summit. In 2024, Fujita Health University was awarded the Forming Japan's Peak Research Universities (J-PEAKS) Program by the Japanese government to establish an innovative academic drug discovery ecosystem and hub of a multi-university consortium for research and education.
Website: https://www.fujita-hu.ac.jp/
About Mr. Ryota Miyake from Fujita Health University
Mr. Ryota Miyake is a medical researcher and student affiliated with the Department of Psychiatry at Fujita Health University School of Medicine in Toyoake, Aichi, Japan. His research focuses on sleep quality, environmental influences on sleep, and objective sleep assessment in psychiatric populations. He has contributed to clinical research examining the relationship between nighttime light exposure and sleep quality in psychiatric outpatients, including patients with schizophrenia. His work includes evaluating actigraphy-measured sleep parameters, sleep efficiency, and environmental factors that may influence sleep. Through this research, Miyake contributes to understanding modifiable factors that could support better sleep management and clinical care.
Funding information
This work was supported by Scientific Research funding from JSPS KAKENHI (grant number: 24K10721) and Takeda Science Foundation.
