This is a randomized placebo- and active-controlled trial for assessing the efficacy of bright light therapy for sleep and mood symptoms in patients with Parkinson's disease

The primary aim of this study is to compare the efficacy of timed-BLT (BLT group) in reducing excessive daytime sleepiness in patients with Parkinson's disease, when compared to a timed-inactivated negative ion generator (active-control group).

The secondary aims of the study are to examine the effect of timed-BLT on other non-motor symptoms, including depression, fatigue; and the quality of life.

Additional analyses will be carried out to examine the efficacy of the timed-placebo as compared to the random-time placebo (placebo group).

Inclusion Criteria:

1. Idiopathic Parkinson's disease diagnosed by neurologist according to the UK Parkinson's Disease Society Brain Bank clinical diagnostic criteria
2. Capable to give informed consent
3. Maintained on stable dose of medications for Parkinson's disease/psychotropic drugs for at least four weeks prior to entry of the study
4. Score 14 or more on the Epworth Sleepiness Scale

Exclusion Criteria:

1. A current or past history of manic or hypomanic episode, schizophrenia, mental retardation, or substance use disorder. (Subjects with depression or anxiety disorders will not be excluded)
2. Unstable medical or psychiatric condition
3. Presence of substantial suicidal risk as judged by the clinician and/or screening instruments
4. Presence of active psychotic symptoms that might impair the ability to consent or validity of the interview
5. Cognitive impairment with score of 19 or below by the Hong Kong version of Montreal Cognitive Assessment (HK-MoCA)
6. Contraindication to bright light therapy: history of light induced migraine. Epilepsy, current use of photosensitizing medications, presence of eye disease, e.g. retinal disease, severe cataract, glaucoma and blindness
7. Significant medical condition/ hearing impairment/ speech deficit lead to incapability in completing clinical interview
8. Regular shift worker or trans-meridian flight in the past three months
9. Enrolment in another clinical trial of an investigational medicinal product or device
10. Subjects who are on exogenous melatonin
11. Patients with deep brain stimulation (DBS) implant
12. Patients with known sleep disorders, eg. untreated severe sleep apnea, restless leg syndrome

The subjects will be explained that the study aims to test the efficacy of the different modalities of non-pharmacological treatments for depression including bright light therapy and the negative ion generator, without mentioning which one is the placebo. An independent outcome assessor will be blinded to the treatment allocation throughout the study.