OBJECTIVE: The present trial evaluated incorporation of bright light therapy in the treatment of chronic nonspecific back pain (CNBP). DESIGN: A prospective, randomized, controlled, multicenter, open design with three parallel trial arms was used. SETTING: Subjects received a novel therapeutic, an expected therapeutic ineffective low dose, or no light exposure at three different medical centers. PATIENTS: A total of 125 CNBP patients reporting pain intensity of ≥3 points on item 5 of the Brief Pain Inventory (BPI) were included. INTERVENTION: Over 3 weeks, 36 active treatment, 36 placebo controls, and 33 controls received 3 or no supplementary light exposures of 5.000 lx or 230 lx, respectively. OUTCOME MEASURES: Changes in self-reported scores of pain intensity (BPI sub-score 1) and depression (Hospital Anxiety and Depression Questionnaire) were the primary outcome measures. Secondary outcome measures were changes in self-reported overall pain sensation (BPI total score), grade of everyday life impairment (BPI sub-score 2), mood (visual analog scale), and well-being (World Health Organization-Five Well-Being Index). RESULTS: Changes in pain intensity were higher (1.0 [0.8-1.6]) in the bright light group compared with controls (0.3 [-0.1-0.8]; effect size D = 0.46). Changes in the depression score were also higher in the intervention group (1.5 [0.0-2.5]) compared with controls (0.0 [0.0-2.0]; effect size D = 0.86). No differences were seen in change scores between intervention vs sham group. CONCLUSION: The present randomized controlled trial shows that light therapy even in low dose could improve depressive symptoms and reduce pain intensity in CNBP patients. Further research is needed for optimizing parameters of frequency, dose, and duration of therapeutic light exposure.