Study	Reason for exclusion
Fleer 2014	The TAU (treatment as usual) group received an invitation to light therapy when first depressive symptoms occurred. Therefore, this study did not fulfil the eligibility criteria for our review which focuses on prevention of SAD with light therapy, beginning the light therapy when participants are still free of symptoms.
Graw 1997	SAD participants were treated with light therapy when they suffered a depressive episode. They were interviewed again 2 to 5 years later. Treatment started when participants already had depressive symptoms ‐ not when they were free of symptoms; therefore, the study was not relevant for this systematic review.
Kasper 1988	Study included participants without depressive symptoms, but also without a history of SAD. As the study investigated preventive effects of light therapy on healthy participants, it was not relevant for this systematic review.
Kjellman 1997	Conference abstract
Lafer 1994	Study investigated treatment ‐ not prevention ‐ of SAD
Meesters 1991	Study investigated whether starting light therapy at an early stage of a depressive episode can prevent a full‐blown winter depressive episode. Included participants already had depressive symptoms when the study started; therefore, the study was not relevant for this systematic review.
Meesters 1993	Study investigated whether starting light therapy at an early stage of a depressive episode can prevent a full‐blown winter depressive episode. Included participants already had depressive symptoms when the study started; therefore, the study was not relevant for this systematic review.
Meesters 1994	Study included participants with a history of SAD and investigated preventive effects of light therapy. However, the study included only 1 intervention group and no control group, therefore, the study was not relevant for this systematic review.
Meesters 1995	Study investigated treatment ‐ not prevention ‐ of SAD
Most 2010	Study investigated prevention of depression and sleep disturbances in the elderly with light therapy. Included participants in this study were diagnosed with major depressive disorder without a seasonal pattern. Therefore, the study was not relevant for this systematic review.
NCT00076245	Study investigated acute and long‐term efficacy of cognitive‐behavioural therapy for SAD alone and in combination with light therapy as compared with solo light therapy. Included participants already had symptoms when interventions were started; therefore, the study was not relevant for this systematic review.
NCT01714050	Study investigated relapse prevention of SAD and compared cognitive‐behavioural therapy, light therapy and a combination of these ‐ not prevention of SAD. Included participants already had symptoms when the study started.
Norden 2000	Study investigated dawn simulation in participants with subsyndromal winter depression. Participants had no history of SAD.
Partonen 1995	Study investigated recurrence ‐ not prevention ‐ of SAD. Included participants already had symptoms when the study started.
Partonen 1996	Study included participants with a history of SAD and investigated preventive effects of light therapy. However, the study included only 1 intervention group and no control group; therefore, the study was not relevant for this systematic review.
Rohan 2007	Study investigated acute cognitive‐behavioural therapy for SAD alone and in combination with light therapy as compared with solo light therapy. This was a treatment study ‐ not a prevention study.
Rohan 2009	Study investigated recurrence of SAD after 1 year of cognitive‐behavioural therapy, light therapy and a combination of these. Included participants already had depressive symptoms when the study started; therefore, it was not relevant for this systematic review.
Rohan 2013	Study investigated relapse prevention of SAD and compared cognitive‐behavioural therapy, light therapy and a combination of these ‐ not prevention of SAD. Included participants already had symptoms when the study started.
Terman 1994	Study investigated whether starting light therapy at an early stage of a depressive episode can prevent a full‐blown winter depressive episode. Included participants already had depressive symptoms when the study started, therefore, the study was not relevant for this systematic review.
Thorell 1999	Study investigated relapse prevention ‐ not prevention of SAD. Included participants already had symptoms when the study started.
WELL 100006	Study investigated preventive effects of bupropion XL in participants with a history of SAD. It is included in the systematic review on efficacy and safety of second‐generation antidepressants; however, as it does not investigate efficacy nor safety of light therapy as preventive treatment, it is not relevant for this systematic review.
WELL AK130936	Study investigated preventive effects of bupropion XL in participants with a history of SAD. It is included in the systematic review on efficacy and safety of second‐generation antidepressants; however, as it does not investigate efficacy nor safety of light therapy as preventive treatment, it is not relevant for this systematic review.
WELL AKA130930	Study investigated preventive effects of bupropion XL in participants with a history of SAD. It is included in the systematic review on efficacy and safety of second‐generation antidepressants; however, as it does not investigate efficacy nor safety of light therapy as preventive treatment, it is not relevant for this systematic review.
Wirz‐Justice 1990	Study investigated treatment ‐ not prevention ‐ of SAD. Included participants already had symptoms when the study started.

SAD: seasonal affective disorder