In a situation where an observer stays inside of a room and looks at the outdoor scene through an window, he obtains two recognized visual space of illumination (RVSI) for the respective spaces. These two RVSIs differ normally as the illumination situation differs between the two spaces . It is possible , however , to equate them by controlling the illumination situation of the room , where the observer experiences a feeling of continuity between the two spaces. By using a normal house as the

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... perimental place the illuminance of a dining room was obtained to assure the continuity point during early morning as well as toward the sunset. It was found a simple linear relation exists between the illuminance in the room and that in the outside when the values were expressed in logarithmic unit . It is suggested to employ the relation to control a room illumination in order to offer the residents the amenity.