In order to identify the characteristics of visual performance of window screens, which include providing sufficient light, reducing discomfort glare and keeping the visibility of the outside view, visual performances of window screens are compared with that of venetian blinds. The apparent openness factor and the average luminance and luminance distribution of the window, which determine the visual performance, are calculated for the window screens and the blinds. The results show the change in the apparent openness factor with the angle between the window plane and the line of the sight for the window screen and the blinds. The window screens are not advantageous to keep both a moderate average luminance and the pattern of the luminance distribution of the window in comparison with the blind, when they are hit by the direct sunlight.
