 SAD is diagnosed on the basis of history and a definitive diagnosis is difficult to make in adolescents. In addition, their symptom profile differs from that seen in adults which would make assessment using any single measure difficult and would require a substantially larger sample size. Therefore in this preliminary investigation we propose to recruit individuals between the ages of 18-64. Because the safety of light treatment in pregnancy has not been established, and because mood effects of pregnancy and recent delivery would complicate assessment of treatment response in this 3-wk trial, only nonpregnant, non-lactating women will be included. 