Effects of environmental lighting on students’ sleep, alertness and mood: A field study in a Chinese boarding school

A field study was conducted in two classrooms to explore the effects of standard and high light levels on sleep, alertness and mood of boarding high school students in Suzhou, China. 79 participants took part in a 7-week study in winter. After 3-week baseline assessments under standard lighting, participants were exposed to 3-week high light levels, separated by a 1-week washout. One group experienced this condition in the morning and the other experienced it in the evening. Horizontal illuminance was recorded in real time during the experiment and converted to eye-level vertical illuminance and equivalent melanopic lux. Sleep wristbands and questionnaires were used. Morning or evening high light levels significantly improved acute alertness during the increased light level hours compared with standard lighting, but there was no significant difference in sleep or mood. Additionally, compared to the evening high light levels, morning condition was significantly associated with longer deep sleep duration, easier falling asleep and lower negative mood. This study is the first to directly correlate high light conditions and timing of light exposure with subjective and objective sleep, alertness and mood of Chinese boarding high school students, which can provide references for the application of healthy lighting in classrooms.