Influence of the irradiance spectrum on solar reflectance measurements

Solar reflectance (SR) is the key performance parameter of cool roof and cool pavement materials. For its assessment, the measured spectral reflectivity of the sample is weighted by a reference spectrum of solar irradiance. Several standard and non-standard spectra are, however, available, taking into account different climate conditions, angle of incidence of the solar beam, and the contribution of the diffuse radiation content. This study is aimed at investigating the impact of using different solar irradiance spectra as specified by existing standards or suggested by qualified research institutions, and verifying if those spectra can yield equivalent SR values from the viewpoint of assessment of standard performance and comparison of commercial products. Several actual material are considered, either white or coloured ones and with assorted spectral behaviour.