Introduction: Dementia is an age-associated neurodegenerative disorder characterized by a progressive loss of neuro-cognitive function and the emergence of a wide variety of behavioral symptoms. Alzheimer's disease (AD) is the most common types of dementia. Sleep disturbances in patients with Alzheimer's disease is common and previous studies from North America, Europe and Japan reported light therapy could improve the sleep circadian rhythm ( rest-activity) disturbances in AD. However, there was no previous Chinese study on light exposure and sleep quality nor the circadian rhythm in Chinese Alzheimer's disease patients. Objective : The objective of the present study was to investigate the association of light exposure intensity with the quality of sleep and behavioural symptoms in Chinese Alzheimer’s disease (AD) patients Method: This was a cross-sectional observational study. 203 Chinese elderly patients with Alzheimer's disease were recruited from the Memory Clinic in Queen Mary Hospital, the University of Hong Kong, from July 2014 to December 2014. Socio-demographic data and comorbid diseases information were collected from all subjects. Their sleep qualities, quantities and conditions of light exposure were recorded with a sleep logbook and light meter. Their cognitive function, disturbing behaviour, depressive mood and quality of life scales were assessed by a semi-structured questionnaire. Light exposure intensity measured by Light meter (Model SDL 400). Measure for cognitive function were the Abbreviated Mental Test (AMT), Behavioral symptoms measured by the Neuropsychiatric Inventory (NPI) and mood by Geriatric Depression Scale. (GDS-15) The association of outdoor or indoor light exposure with sleep quality and quantities were analyzed by descriptive, bivariate and multivariate analyses. Main outcome measures: The main outcome measure was the sleep quality and quantities of patient, measured by Pittsburgh Sleep Quality Index. (PSQI) Results: 203 subjects (60 males and 143 females) were recruited. 70.4 % of the studied subjects were females. Male to female ratio is 1:2.38. Mean age of them was 81.6 years. The mean (SD) scores of the recruited were: AMT = 4.5 (2.9); PSQI = 6.9 (3.4); NPI =14.4 (17.2); GDS-15= 4.3 (2.8); QOL-AD (patients) = 30.7 (4.9); QOL-AD (caregivers) = 29.5 (4.7) respectively. In bivariate analysis, the Global PSQI score was significantly associated with the morning and afternoon outdoor light exposure. (r = -0.634 and -0.466, respectively) For the total light exposure and mean light exposure, both of them showed strong significant negative correlation with Global PSQI score. (r = -0.769 and -0.769 respectively). Mean (SD) light exposure per day for morning and afternoon outdoor setting were 2372.9 lux (2564.7) and 1090.8 lux (1894.6) respectively. Mean(SD) light exposure per day was 1196.7 lux (866.1) Gender identity showed significant correlation with Global PSQI score (r = 0.034). Global PSQI score was significantly associated with the NPI total score (r = 0.261, p<0.001), the GDS-15 score (r = 0.336, p<0.001), the QOL-AD for patients (r = -0.257, p<0.001), and the QOL-AD for caregivers. (-0.313, p<0.001) In multivariate analyses, using general linear models, the Global PSQI score was highly independent associated with the total light exposure (p=0.000), and significantly associated with the NPI score and Gender (p = 0.011 and 0.021), after adjusting for potential confounders in bivariate analysis. (i.e. gender, activity of daily living status, hypertension and Chronic obstructive airway disease). Confounding factors were NPI and gender. Conclusion: In the present study, We found the intensity of natural light exposure was related to good sleep quality in older Chinese Alzheimer’s disease patients with age 65 years and above in Hong Kong as well as lesser episode of behavioural symptoms. Hence, daily outdoor light exposure is highly recommended for persons with Alzheimer’s disease. / published_or_final_version / Medicine / Master / Master of Medical Sciences