Effect of the Combined Use of Morning Blue-Enriched Lighting and Night Blue-Suppressed Lighting (MENS) on Sleep Quality

Objectives: Previous studies have shown that exposure to blue-enriched light in the morning or blue-suppressed light in the evening may positively affect sleep. In this study, we aimed to investigate the effect of combination of morning blue-enriched and night blue-suppressed lighting (MENS) on sleep quality. Methods: Thirty workers were recruited. After one-week baseline evaluation, the participants were randomly assigned to either an experimental or a control group. Both were exposed to light in the morning and evening for two weeks. The experimental group used a lighting device emitting 480-nm wavelength maximized light in the morning and minimized light in the evening, while the control group used 450-nm wavelength light in the same way. The final evaluation was conducted using questionnaires and sleep diaries. Results: Both groups showed statistically significant improvements in seven out of nine sleep quality measures (p<0.05). The experimental group showed improvement in sleep latency and sleep fragmentation compared to that in the control group (p=0.017). The control group showed improvement in wake after sleep onset. The ratio of participants who showed improvement and transitioned from abnormal to normal values was significantly higher in the experimental group for sleep latency (p=0.046) and in the control group for fatigue (p=0.012). Conclusions: The findings suggest that the use of MENS significantly improves sleep quality. Although the difference in the improvement effect between different wavelengths of blue light was not substantial, the use of 480-nm blue light appears to be effective in reducing sleep latency.