Each session lasts 1h30 and will be conducted in a room prepared for this purpose. It will include three ceiling light therapy Elecolight® QUEBEC (including 10,000 lux lamps) placed above the center of a rectangular table with 6 seats, about 50/60 cm (central device) or 80 cm (on both side of the central device) above the table plane. So patients sat around the table to make occupational therapy activities while receiving bright light. The arrangement will ensure that the lamp will be at a distance of 60-80 cm from the face of patients. The light output power in areas where patients will sit will be measured with a light meter to check the adequacy of the provision. This arrangement will allow patients to receive the illumination in "green" requirements while achieving a group activity. The occupational therapy activities will be chosen to be performed on the table: drawing, dominos, cards, etc ... Given the particularities of the patients studied (patients with Alzheimer's disease with behavioral problems), this mode of administration seems preferable to the conventional method (patient to sit still in front of the light box), which would likely be encumbered with a high failure rate with these patients.