Photoreceptor-directed light therapy in Parkinson’s disease

Supplemental light therapy: Arm 1: High melanopsin light Arm 2: Low melanopsin light The ‘high’ melanopsin state has a relatively increased spectral component around the peak sensitivity of the melanopsin photopigment. The ‘low’ melanopsin state has a relatively reduced spectral component in that range compared with the ‘high’ state. The melanopsin contrast between these states is approximately 25%. Each state’s total radiometric power is approximately 1.4W/m^2 (watts per square metre) and 2.8W/m^2 respectively, measured at 30cm. Of this, 0.445W/m^2 and 0.56W/m^2 respectively is acting on melanopsin photoreceptors, and both states have 0.808W/m^2 attributable to photometric luminance. Both states will not deliver more than the industry standard 10,000 lux at a 16cm viewing distance (e.g. approximately 5,000 lux). The participant will view the light for 30 minutes daily at home for 4 weeks. The participant will be instructed face to face by one of the research team members on the use of the light. We personalize the timing (morning or evening) of the daily (30min) light exposure based on a person’s chronotype to control for individual differences in activity and alertness in the morning and evening. Chronotypes will be determined with the Morningness Eveningness questionnaire. Actigraphy data provide an additional control measure to ensure adherence to the light intervention methodologies; that is, if the participant incorrectly uses the light, the actigraphy data will return lower light exposure when light box should have been used.