In this study, we tried to measure spectral hemispherical transmittance of piling quartz glass plates with or without double-layer anti-reflection coatings. Overall, the measured spectral transmittance under the conditions of both single plate and 8 plates was consistent with numerical simulation result based on one-dimensional model. However, there was unexpected periodic fluctuation in the wavelength range from 1.5 to 2.0μm. It was shown that the fluctuation proceeded from spectral characteristics of blazed grating for polarized radiation. In addition, the difference between measured and theoretical result in the wavelength region was due to experimental conditions such like use of wave-guide constructed Au mirrors and the quartz glass plates with finite size. As a result, in consideration for the restrictions, it could be regarded that selective transmission of this optical filter for diffuse irradiation was verified in experimental way.