Bright light therapy (BLT) was an initial treatment for those with seasonal affective disorder. Later studies found it to be beneficial for nonseasonal depression. BLT may be beneficial for patients in the depressive phase of bipolar disorder (BD). Depression lasts longer than mania in BD. Sleep complaints are a common consequence of mood disorders like depression. When the fall and winter months arrive, there is less sunlight. This disrupts your internal circadian system. Circadian disruption is commonly associated with functional impairment and a poorer quality of life. Regulation of the circadian rhythm is a potential treatment for BD.