40 Hz Flickering for Insomnia in Parkinson's Disease

Inclusion Criteria: * Diagnosis of Parkinson's disease according to established clinical criteria (e.g., Movement Disorder Society criteria). * Age between 50 and 75 years. * Disease duration ≤ 10 years and Hoehn and Yahr stage ≤ 3 in the "on" state. * Clinically significant insomnia, defined as Parkinson's Disease Sleep Scale-2 (PDSS-2) total score ≥ 18 points and/or meeting diagnostic criteria for insomnia. * Stable antiparkinsonian medication regimen for at least 4 weeks prior to enrollment. * Able and willing to comply with study procedures and provide written informed consent. Exclusion Criteria: * Secondary insomnia primarily due to severe systemic diseases or major psychiatric disorders (e.g., psychosis, severe depression or anxiety) or substance abuse. * History of epilepsy, photosensitive seizures, photosensitive dermatitis, or other conditions in which flicker light stimulation is contraindicated. * Severe visual impairment or eye diseases that would interfere with light stimulation or safety assessment. * Unstable or severe medical conditions (e.g., uncontrolled cardiovascular, hepatic, renal, or endocrine disease) that, in the investigator's opinion, make participation unsafe. * Participation in another interventional clinical trial within the past 3 months. * Inability to complete study procedures or follow-up due to cognitive, physical, or social reasons.