Solar reflectance of colours for external paints obtained by spectrophotometric analysis

Abstract

External colour has a strong influence on the thermal performance of buildings. The effects of solar heat gain, as a function of the reflectance of external surfaces of the buildings are well known. However, there is little information available about this parameter. This article aims to contribute to fill this gap. Samples of paints of different colours are analysed as a function of their reflectance to solar radiation. The technique used is the spectrophotometer analysis. Such a method provides not only the total reflectance, but also the percentage along the solar spectrum. Two kinds of samples are used: painted cement mortar tablets and samples obtained from catalogues. Since these samples do not present specular reflection, the integrating sphere is used, an accessory that detects the diffuse distribution of light. The results show that in some cases darker colours present lower reflectance than lighter ones, due to lower values in the near infrared region.