Low-E glass and gray films for building windows are considered to have an effect of cutting incident solar radiation without intercepting of visibility through windows. We analyzed of spectral transmittance and spectral reflectance of gray films for building windows considering the change of incident angle of solar radiation against vertical glasses. As incident angle of solar radiation increases from 0° to 70°, spectral transmittance increases. And also we clarified its effect on decrease of room temperature by numerical simulation. In the case of a building with an atrium which is located in Kashiwazaki, Niigata, whose total floor area is about 800m2 and whose south wall is covered with windows, solar heat gain was reduced 55% in summer seasons, and 46% in winter seasons.
