Depression during pregnancy is a high impact disease affecting 5-10% women. It negatively affects pregnancy, birth outcome and (intrauterine) child neurocognitive development. Therefore, early detection and treatment of depression during pregnancy can benefit both mother and child. Since treatment with antidepressant medication is controversial because of its unknown effects on intrauterine development, alternative non-pharmacotherapeutical interventions are of high relevance. Bright light therapy (BLT) has proven to be effective in depression, with few adverse reactions. Therefore, it is an attractive candidate treatment for pregnant women with depression. Evidence suggests that the effect of BLT is mediated by improved circadian functioning, as indirectly indicated by enhanced sleep and hormone (cortisol and melatonin) rhythms in our previous studies.1 This is of particular interest, since elevated maternal cortisol levels during pregnancy are found to be a mediator between maternal depression, and adverse pregnancy and child developmental outcomes. This shared pathway defines BLT as a rational candidate for investigating a therapeutic role in depression in pregnancy. This study is a randomized, double-blind, placebo-controlled clinical trial comparing the antidepressive effects of BLT with placebo in 150 pregnant women with depression. The primary aim of this study is to investigate whether BLT is an effective treatment for depression during pregnancy compared with low-intensity light therapy (placebo). Secondary aims of the study are to demonstrate the effect of BLT on sleep quality, endocrine function during pregnancy, and on delivery outcomes; if any of these effects are present, their mediating role on mother and child outcomes will be tested.