Abstract: Objective: To systematically review the effects of different illumination parameters of light therapy, such as the light timing, light duration, light intensity, and spectral distribution, on helping to improve sleep quality in patients with Alzheimer's Disease. Methods: A comprehensive search of Chinese and English databases on the studies of light therapy on sleep disorders in patients with Alzheimer's Disease was conducted. The studies were selected according to the inclusion and exclusion criteria and were critically evaluated by two reviewers. Data of included studies were extracted, and only descriptive analysis was conducted. Results: Eight randomized controlled trials and 4 cohort studies were included. Previous studies have shown that: a) 9:00-11:30 am or 5:00-8:00 pm is the best time of the day to exposure light; b) 2 hours of light per day for more than two weeks is the basis for ensuring effective light, and it can improve the sleep disorders of patients and has higher safety; c) the light intensity of 3000-8000 lux can substantially improve the quality of sleep; d) short-wave blue light and white light can effectively correct circadian rhythm disorders, but further research is needed. Conclusion: The settings about the timing, duration, intensity and spectral distribution of the light therapy are the elements that need to be considered. At present, there are no standards for light parameters. Further studies should explore different light parameters of light therapy and observe long-term effects of sleep disorders in patients with Alzheimer's Disease.

Key words: light therapy; Alzheimer's Disease; dementia; sleep disturbances; systematic review