Seasonal Affective Disorder (SAD) is characterised by the onset of depressive illness during certain months, particularly in winter, when there is less natural sunlight. The depression generally subsides during spring and summer.

SAD may be effectively treated with light therapy; however, nearly half of those with SAD do not respond to light therapy alone. Antidepressant medication and psychotherapy can help reduce SAD symptoms, either as standalone treatments or in combination with light therapy.