OBJECTIVE: Poststroke insomnia is common and negatively affects stroke recovery. The objective of this study was to determine the effectiveness of bright light therapy for mild-to-moderate stroke patients with insomnia. METHODS: This study was randomized, double blind, and placebo controlled. A 2-week trial was conducted on patients with mild-to-moderate stroke who had poststroke insomnia. Only patients who had experienced a first episode of stroke were enrolled in this study. Sleep parameters were measured using the Actiwatch Spectrum Pro for 7 days before and after light therapy. The instrument specifically collected data concerning sleep, mood state, fatigue, and subjective quality of life. Participants with poststroke insomnia received bright light therapy (10,000 lux) or placebo therapy for 30 minutes in the early morning. A total of 112 eligible participants entered the study, but only 56 patients were randomized to treatment (27 to bright light therapy and 29 to placebo therapy). RESULTS: Results from analysis of variance showed that the mean change of sleep latency (F(1,55) =4.793, p = .033) and sleep efficiency (F(1,55) = 5.625, p = .022) were significantly superior in bright light therapy over placebo. Bright light therapy resulted in significant improvements in daytime sleepiness, fatigue, mood, and quality of life in study participants (p < .05). CONCLUSIONS: Bright light therapy is a nonpharmacological treatment of early, poststroke insomnia in patients who had a mild to moderate stroke. In addition, bright light therapy is effective for the treatment of daytime sleepiness, fatigue, and depression and for improving quality of life in patients with poststroke insomnia. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04721574.