Generally, it is recommended to illuminate the desktop at 750 lx to recognize objects on it in office building environmental design. For evaluation of productivity, however, stress by the strong light, eye exhaustion or influence on biorhythm by long exposure to light stimulation must be taken into account as well as easiness of recognition. In this paper, it especially pays attention to the change of person¡Çs biorhythm between the days, and it reports on the result of experiment for comparison of the relation between a lighting control and conservation of energy that improves Productivity of office worker.