Abstract
To control artificial lighting by utilizing daylight is one of the important methods to save lighting energy. In this paper, we employed a model of an office room with light-diffusing-fixed slats blind attached on a window face, and discussed, among various electric lighting controls, the controlling condition of turning on-off control system introduced comparatively with ease. The problem with on-off lighting is its complicatedness and unpleasantness due to utilizing efficiency and illuminance change caused by on-off turning of artificial lighting for change of daylight. To solve the problem, the following two controlling conditions were considered : 1) to provide the wider range with the set-up illuminance to control, 2) to place regular time intervals between turning on and off. Hereafter, by providing the set-up point with each controlling condition, we attained to the favorable controlling method from four points of views, that is to say, daylight utilizing efficiency, frequency of on-off turning, fault turning-off ratio and surplus turning-on ratio. Our observation obtained the following results : 1) When illuminance value was set-up at the turning-off level ranging from 10 % to 30 % in-crease, the utilizing efficiency and the frequency of on-off turning decreased. However, when the illuminance level difference between turning-on and turning-off was made bigger, the surplus turning-on ratio in-creased. 2) When time intervals of operation between turning-on and turning-off and vice versa are set wider, although the utilizing efficiency did not differ so much, the frequency of on-off turning decreased ; in particular, at in-tervals less than ten minutes, the frequency of on-off turning decreased sufficiently. 3) In the same manner, when on-off turning control is carried out at twenty minutes intervals, both surplus turning-on ratio and fault turning-off ratio increased, which is not the favorable controlling condition. Our observation showed that what is essential to decrease the frequency of on-off turning with-out causing inefficiency is to place wider time intervals, rather than to set up the illuminance level for turning-off. Moreover, when stepped light control, the method to control each row one after another, is carried out, although the on-off turning must be made more frequently, the utilizing efficiency is enhanced. By this method, because of the stepped on-off turning, the change of the illuminance bacomes smaller and its psychological effect is notable.
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