This paper aims to establish a design system of the shading windows which achieve a balanced flows of visual information between the inside and the outside of a room. For this purpose, the relationship between the visibility level and the physical condition of the object seen through the shading of a window must be known. In this paper, the calculating method of the apparent luminance of a visual target seen through a lace curtain was established. In the calculating method, three optical properties of various race curtains, the rate of passage luminance, the property of transmission, and the property of reflection, are required. So these optical properties of five kinds of lace cloths which have different formal characteristics were measured.
