ENLITE PD: A Randomized Clinical Trial of Light Therapy for Impaired Sleep in Parkinson's Disease

Light therapy (LT) in Parkinson's disease improves sleep. Specific LT parameters require further study, including optimal frequency.

We aimed to determine if once- or twice-daily bright white light therapy (BWLT) improves sleep. Secondary aims compared once-weekly BWLT to twice-daily dim red light therapy (DRLT) as controls, estimated effects on fatigue, and adherence.

A 16-week, randomized, phase 2, sham-controlled, dose-selection trial to select the superior BWLT frequency based on change in Parkinson's Disease Sleep Scale-2 (PDSS-2), participant burden, and safety. Participants were randomized to 8 weeks of twice-daily BWLT, once-daily BWLT, once-weekly BWLT, or twice-daily DRLT. An improvement of ≥1.7 points in 8-week change of PDSS-2 by daily BWLT relative to either control warranted advancing to a phase 3 trial.

A total of 150 participants were randomized (mean [SD], 67 [8.6] years; 57 [38%] female; PDSS-2 17.1 [6.7]). Mean 8-week change from baseline in PDSS-2 score improved (twice-daily BWLT -2.6 [95% CI: -4.4, -0.7]; once-daily BWLT -1.5 [-3.3, 0.3]; once-weekly BWLT -0.4 [-2.2, 1.4]; twice-daily DRLT -1.8 [-3.6, 0.1]) but did not meet criteria for advancing. Mean 8-week change from baseline in Parkinson's Disease Fatigue Scale (PFS-16) score improved (twice-daily BWLT -6.4 [-9.8, -3.0]; once-daily BWLT -2.2 [-5.5, 1.1]; once-weekly BWLT -0.5 [-3.9, 2.8]; and twice-daily DRLT -3.8 [-7.3, -0.4]). Mean adherence to LT was 63%-86%.

ENLITE-PD did not meet the criteria for advancing daily LT to a phase 3 trial. LT was safe and well-tolerated with good adherence. Once-weekly BWLT was a non-inferior control compared with twice-daily DRLT. © 2025 International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.