| quotient of five times the sum of the area of the walls bounded by the working plane and the plane of the luminaires and the sum of the areas of the working plane and the plane of the luminaires, used in the calculation of the utilization factor or utilance Note 1 to entry: The room cavity ratio is expressed by the formula where a and b are the dimensions of the sides of the room and h the mounting height, that is the distance between the working plane and the plane of the luminaires. Note 2 to entry: See also "ceiling cavity ratio" and "floor cavity ratio". Note 3 to entry: The room cavity ratio has unit one.
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