Alternative methods to identify the solar absorptance of opaque surfaces

Abstract

In this paper, two alternative methods to identify the solar absorptance of opaque surfaces are presented. In the first method, samples painted with different paint colours were classified according to the RGB and HSL digital chromatic systems. In the second method, the reflectances of the samples were measured with a low cost spectrometer for radiations in eleven different wavelengths, from 470 nm to 940 nm. Based on reflectance data obtained in laboratory, equations were developed to estimate reflectances for the visible and the total range of the solar spectrum, according to the spectrometer and the RGB and HSL data. The reflectances obtained in laboratory were adjusted to the standard solar spectrum in order to indicate the amount of relative energy that is reflected for the surfaces when exposed to solar radiation. The results show that the alternative methods presented in this paper are reliable and accessible for specialists and designers, which will be useful for obtaining reflectance and absorptance data more realistic than those presented in existing published tables.