Treatments: Intervention group: patients will participate in a program of bright light therapy realised during a one-hour sessions of occupational therapy,. These sessions will be realised for groups of 6 patients and will be done every week day, at late morning, for 4 consecutive weeks). During the session, patients will be exposed to 10000 lux-bright light. Patients of control group will participate in a program of occupational therapy of same duration and rhythm, realised in standard light conditions (about 300 lux).