||The quantity and arrangement of luminaires are determined by the interior lighting calculations. For efficient interior lighting design, it is important to consider the required parameters of the lighting calculations. Zonal cavity method, which is a kind of the lumen method, is used for the calculation of the average illuminance on the workplane in an interior space. Important factors of the method are cavity ratio, CU(coefficient of utilization), and light loss factor. A CU varies with a kind of luminaires and is affected by surface reflectances of space. For this, the data from CU computation were analyzed with the same lumens and different candle power distribution. This paper analyzes the changes of CU on the candle power distribution of luminaires, surface reflectances of space and room cavity ratio.