Background Bright light therapy (BLT) is a well-established treatment for seasonal depression. In the last two decades, the interest in BLT has expanded to involve other nonseasonal types of depression. The role of BLT for nonseasonal depression remains unsettled. In view of the growing number of studies in this area, this review aimed to assess the efficacy of BLT in nonseasonal depression.

Methods We searched Pubmed; Scopus; PsychINFO; Evidence Based Medicine Guidelines and Cochrane Library until December 2015. The Standardized mean difference was calculated to assess the efficacy of BLT in nonseasonal depression. Data were subgrouped according to different study characteristics. Heterogeneity was assessed by examining the I2 index.

Results Nine trials met the inclusion criteria. After employing the more conservative random-effects model, the overall model showed a significant reduction of depressive symptoms after BLT administration (SMD=−0.62, P<0.001, I2=37%). In particular, BLT appears to be efficacious when administered for 2-5 weeks (SMD=−0.78, P<0.001, I2=0%), and as monotherapy (SMD=−0.71, P<0.001, I2=18%). Studies of BLT for perinatal depression have found statistically insignificant improvement (SMD=−0.17, P>0.05, I2=44%).

Limitations The overall heterogeneity of the included trials was moderate. The participants were not adequately blinded to the intervention. The sample size was small for certain subgroups. The long-term effect of BLT on depression was not explored.

Conclusions BLT appears to be efficacious, particularly when administered for 2–5 weeks’ duration and as monotherapy. There is an obvious need to optimize the duration and intensity of exposure, the timing and the duration of treatment sessions.