This paper deals with a method for using daylight in a building lighting system. The use of daylight is one of the most effective methods to cut costs and energy for building lighting. And exposure to bright light at the critical times of the morning improves some mental and physical health problems that the disorder of biological clock causes. In this study, we performed a simple experiment in order to investigate the biologic effects of the short time exposure of daylight. It is expected that the Bright light treatment would be also applicable in a rest space where people stop at only for short break. The experiment was carried out in February of 2009 in Japan. 16 healthy young college students participated in this experiment for 5 days. They maintained a regular sleepwake schedule beginning from 3 days before the experiment period and throughout the experiment period. The subjects performed a task-set program on the flat panel display during the 1 hour working sessions, from 9:30 to 10:30 (session 1), 11:00 to 12:00 (session 2), 13:00 to 14:00 (session 3), 14:30 to 15:30 (session 4), and 16:00 to 17:00 (session 5). The light intensity in the working space was set below 700 lx by the fluorescent lights every time in the experiment period. In the resting space, the light intensity was controlled with the window blind. In the Two days under the non-circadian condition, the light intensity was set below 700 lx by pulling down the window blind. In the other three days called the circadian condition, The light intensity was controlled by the window blind to be within a range from 1600 lx to 2400 lx during the break between session 1 and 2 (from 10:30 to 11:00), session 2 and 3 (from 12:00 to 13:00). The light intensity was gradually decreased to 700 lx by closing the window blind slowly after session 3. In order to check the phase of cortisol secretion rhythm, a serial saliva sampling was taken at each interval between task sessions (at 9:30, 12:00, 13:00, 15:00 and 17:00). Furthermore, the saliva samplings were also taken at midnight (at 23:00 and 24:00) over the experimental period. And in order to check the sleep efficiency, the body movements of the subjects during the sleeping (from 24:00 to 7:00) were measured with the 3D Accelerometer (AirSense: Bycen). Based on the results of the experiment, the following effects of Short time exposure of Bright light in the morning on the Resting time were clarified. After the short time exposure of the Bright light in the morning in the resting space, 1) Almost all the peaks of the amount of the cortisol secretion were at 9:30 in the morning. Under the circadian condition, the amounts of the cortisol secretion during Day2 was larger than Day1 in the morning (p=0.017). Under the non-circadian condition, the amounts of the Cortisol secretion during Day2 was smaller than Day1 in the morning (p=0.005).By comparison the amounts of the cortisol secretion in second day under each condition, the amount of the cortisol secretion under circadian condition was significantly larger than that under the non-circadian condition (p=0.003). These results suggest that the arousal level of the subjects in the morning to improve under the controlled lighting conditions with the short time exposure. In order to further observe this tendency, it might be necessary for the subject to spend more than 2 days under the controlled Bright lighting conditions. 2) The sleep efficiency during the bedtime from 2:00 to 7:00 was derived based on the determination (Figure 4). Under the circadian condition, the sleep efficiency of 15 subjects except for one subject was higher than that under the non-circadian condition. Including the data of the subject, the significant difference was found between the sleep efficiency of the first day of non-circadian condition and the sleep efficiency of the first day of circadian condition (significant level 10%, p=0.098).