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