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

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

Objectives: 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.

Methods: 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.

Results: 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%.

Conclusions: 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.