Morning light conditions before waking up can impact how restful your sleep feels.
Sleep is an essential part of daily life, yet modern lifestyles and constant exposure to technology have led to reduced sleep duration and increased fatigue. Despite its importance, the bedroom environment, including factors like lighting, noise, and temperature, is often overlooked in residential design.
Most sleep studies rely on artificial lighting due to its controllability, but researchers at Osaka Metropolitan University suggest that natural light may better replicate real-life conditions.
To explore this, Xiaorui Wang, a student at the Graduate School of Human Life and Ecology, and Professor Daisuke Matsushita led a study investigating whether introducing moderate levels of natural light into the bedroom shortly before waking could enhance alertness in the morning.
The Experiment and Conditions
The research team designed an experiment involving 19 participants. They tested three conditions using light-shielding curtains and motorized devices:
- Condition IA: Natural light was introduced 20 minutes before waking.
- Condition IB: Natural light was allowed from dawn until waking.
- Condition CC: No natural light was introduced before waking.
After each session, participants’ sleepiness, alertness, and fatigue were measured with an electrocardiogram, electroencephalogram, and a survey.
Results revealed that participants were less sleepy in IA and IB conditions than in CC. In addition, IA was found to be one of the most effective methods for improving wakefulness, as too much light in IB caused adverse effects.
“In the future, we hope to control natural light in the sleep environment as it changes with the seasons and time of day, and to clarify how to introduce natural light that is suitable for a more comfortable awakening,” stated Professor Matsushita.
Reference: “Natural light control to improve awakening quality” by Xiaorui Wang, Yangcheng Gu, Jihui Yuan and Daisuke Matsushita, 14 February 2025, Building and Environment.
DOI: 10.1016/j.buildenv.2025.112733
The study was funded by the Japan Society for the Promotion of Science and JST SPRING.
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