Bright Light Therapy for Non-motor Symptoms in Parkinson's Disease

Inclusion criteria: 1. Diagnosis of idiopathic PD as defined by the United Kingdom PD Society Brain Bank Criteria 2. PD Hoehn and Yahr stage 2-4 3. Pittsburgh Sleep Quality Index (PSQI) score ≥ 5 4. Treatment with levodopa and/or dopamine agonist; adjunctive PD medications will be allowed 5. Stable dose of PD medications for at least 4 weeks prior to the study screening. Exclusion criteria: 1. Atypical or secondary forms of parkinsonism 2. Co-existent significant sleep apnea (as assessed by polysomnography- derived apnea/hypopnea index ≥15 events/hr of sleep) 3. Co-existent restless legs syndrome (RLS), as assessed by the International Classification of Sleep Disorders (ICDS) diagnostic criteria for RLS 4. Cognitive impairment as determined by the Mini-Mental State Examination (MMSE) score of ≤ 26 5. Presence of depression defined as the Beck Depression Inventory (BDI) score \>14 6. Untreated hallucinations or psychosis (drug-induced or spontaneous) 7. Use of hypno-sedative drugs for sleep or stimulants; participants will be allowed to taper these drugs and will become eligible 4 weeks after the taper is completed 8. Use of Selective Serotonin Reuptake Inhibitors (SSRIs) / Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs) antidepressants, unless the participant has been on a stable dose for at least 3 months prior to the screening 9. Use of medications known to affect melatonin secretion, such as lithium, alpha- and beta-adrenergic antagonists 10. Shift work, currently or within the prior 3 months 11. Travel through ≥ 2 time zones within 60 days prior to study screening 12. Hematocrit \<32 mm3 13. Pre-existing glaucoma/retinal disease contraindicated for light therapy (LT) 14. Dense cataracts 15. Use of medications known to photosensitize retinal tissue (phenothiazines, chloroquine, amiodarone, St. John's Wort) 16. Unstable/serious medical illness. 17. Pregnancy