OBJECTIVES: The aim of present conceptual paper is to provide an analytical framework for efficacy evaluation of light therapy in mood disorders. Up to now, the light therapy in Germany is only recommended for seasonal affective disorder (SAD), because clinical trials with other forms of affective disorders report conflicting results. To understand how light unfold its effects, three light pathways between retina and different brain areas can be distinguished according to Boyce (2003): circadian, visual, and perceptual pathways. Previous research focused only on circadian pathway and suggested modulation of chronobiological cycle as mechanism explaining how light decreases depressive symptoms. However, recent research points out that the exact underlying mechanism is still unknown. Thus, it is important to develop a framework that includes underlying processes besides circadian mechanism. METHOD: A conceptual framework was developed using linked mechanisms approach and including explorative literature review to: 1) efficacy of light therapy, 2) relationship between light and visual or perceptual outcomes. For this step, recommended visual and perceptual (psychological) criteria were defined. 3) relationship between criteria from step 2 and mood disorders. Based on the review findings, mediation effects were proposed. RESULTS: The results revealed positive relationship between bright light and psychological processes such as affect, productivity, concentration. Moreover, negative affect was related to different mood disorders. CONCLUSION: A wide range of underlying processes can be considered for the efficacy evaluation of light therapy. Present conceptual paper suggests a linked mechanisms approach based on moderated mediation model with light therapy (X), psychological processes (M) and the efficacy of therapy (Y). Considering conflicting results of light therapy in non-SAD disorders, the form of mood disorder is suggested as first stage moderator (W).