Experimental evaluation of Alta II spectrometer and its application in the Brazilian standards

Abstract Solar reflectance and solar absorptance are directly responsible for the behaviour of surfaces concerning incident solar radiation. The Brazilian regulation related to the thermal and energy performance of buildings has sought to include such properties in its analysis criteria. The objective of this paper is to analyse the accuracy and repeatability of reflectance measurements using the Alta II spectrometer, as well as the influence of ambient light and surface roughness on the measured values. Three series of measurements were performed by varying: the spectrometers used, the exposure to light, and the roughness of the measured surface (flat painted samples or texture painted walls). Measurements were also performed using the Lambda 1050 spectrophotometer as a reference. The analysis showed that the results may be highly inaccurate. Therefore, the Alta II spectrometer should be used with caution. The experiments showed uncertainty of about ±0.10 in the absolute values of solar reflectance (for reflectance ranging from 0-1). Thus, the Alta II spectrometer user must consider such an error. It was also concluded that Alta II should only be used to analyse flat surfaces and it is important to ensure that measurements are carried out preventing light leakage through contact between the equipment surface and the sample.