Exploring the Key Parameters for Indoor Light Intervention in Treating Neurodegenerative Diseases: A Systematic Review

Light, essential for health and well-being, has shown promise for treating neurodegenerative diseases (NDDs). Indoor light intervention (ILI) has become a widely utilized approach in NDD treatment. This review aims to summarize the current literature on ILI for NDDs, analyze its efficacy across various studies, and identify optimal treatment parameters. We searched research articles published from January 1, 1990, to September 30, 2023, in four databases (Web of Science, PubMed, Embase, and Scopus). Single-factor empirical analysis and multi-factor model analysis were conducted for the key treatment parameters (i.e., light wavelength, intensity, and exposure pattern). This review was based on 47 articles that met inclusion criteria, of which nearly 70% focused on Alzheimer’s disease and dementia. Results indicate that light in the 500 – 550 nm and 800 – 1,080 nm range yielded better intervention results. Light in 500 – 10,000 lux was more effective than 0 – 500 lux in visible light, while in near-infrared (NIR) light, a lower power density (15 – 30 mW/cm2) brought more treatment improvement than a higher power density (40 – 90 mW/cm2). Visible light interventions in the morning and afternoon yielded comparable intervention effects, whereas the therapeutical efficacy appeared to decrease with the number of treatment days increasing (20 – 60 days). The findings show that optimizing the wavelength and intensity in ILI can significantly improve the therapeutic effects of NDDs. Our review provides a fundamental reference to enhancing the use of ILI in treating NDDs and optimizing lighting design for healthy buildings.