Exploring the key parameters for indoor light intervention measures in promoting mental health: A systematic review

Indoor lighting can regulate human mood and sleep, further alleviating mental disorder symptoms. Indoor light intervention (ILI) has been demonstrated as therapeutic for mental disease but lacks standardized guidelines for key parameter settings. This review aims to explore the optimal parameters for widely utilized ILI. We conducted a thorough review of research articles published from 1990 to 2023 in the Web of Science, PubMed, and Scopus databases following the PRISMA guidance. Out of a total of 95728 records, 40 eligible studies were analyzed. We subsequently empirically summarized the ILI’s key parameters (i.e., wavelength, illuminance, and exposure time) into each category and compared the therapeutic effects among different ILI groups within each category. Furthermore, we conducted a multivariate model analysis to identify the optimal parameters further while controlling for confounding factors. Results indicate that ILI was mainly used for treating depressive disorders, accounting for 88% of the included articles. Notably, 450 – 550nm peak wavelength light exhibited superior therapeutic efficacy compared to other wavelengths. Light illuminance within 2500 – 10000 lux correlated significantly and positively with efficacy. Morning ILI appeared more effective than evening ILI, and the efficacy increased with the number of treatment days. Optimizing light wavelength, illuminance, and exposure time of indoor light intervention can significantly enhance its therapeutic effects on mental illness. Our review provides a fundamental reference for improving the use of indoor light intervention in treating mental disorders and optimizing indoor lighting design for a healthy indoor environment.