2- versus 4-hour evening phototherapy of seasonal affective disorder.

Seasonal affective disorder (SAD) has been successfully treated with bright light, and morning exposure has been deemed more effective than exposure at other times. Evening treatment may offer a practical advantage, but the optimal duration of exposure has not been established. Six SAD patients were treated at home for 1 week with 2500 lux of light given either from 6 p.m. to 8 p.m. or from 6 p.m. to 10 p.m. using a counterbalanced crossover design with a minimal withdrawal period of 1 week between conditions. Both treatments were effective in reversing SAD symptoms, but neither treatment was superior. These results suggest that evening phototherapy for as little as 2 hours may be a useful and reasonable alternative for the treatment of SAD.