We propose an approximate method of calculating the working plane illuminance in a room containing fixtures. This method requires only one-eighth as many calculated form factors as conventional methods, takes little time, and can use a small memory. However, it must calculate a great many view functions which are determined by the ability of the centre or some part of the arbitary element tolsquo;seersquo; the centre of other elements. This paper describes the effect of room fixtures on the floor illuminance distribution in a room with a louvered light source having either a narrow or wide angle. The results show that it does not depend on the luminous intensity distribution of light source. It also proposes a simple method of predicting the floor illuminance distribution in such a room and presents results that agree well with the approximately calculated ones.
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