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.摘要：太阳反射比与太阳吸收比直接决定了表面在入射太阳辐射作用下的响应特性。巴西建筑热工与能源性能相关法规已将此类物性参数纳入分析判据体系。本文旨在评估Alta II型光谱仪（Alta II spectrometer）的反射率测量准确性与重复性，同时探究环境光与表面粗糙度对测量结果的影响。本研究开展了三组对照测量，分别调控所用光谱仪、光照暴露条件以及被测表面粗糙度（涵盖平面涂装试样与带纹理涂装墙面）三个变量；同时以Lambda 1050型分光光度计（Lambda 1050 spectrophotometer）作为参考设备开展测量。分析结果表明，该光谱仪的测量结果可能存在较大误差，因此使用Alta II型光谱仪时需谨慎操作。实验显示，当太阳反射比处于0~1区间时，其绝对值的测量不确定度约为±0.10，相关使用者必须将该误差纳入考量范围。此外研究还得出结论：Alta II型光谱仪仅可用于平面表面的分析，且需确保测量过程中避免设备表面与试样接触处出现光线泄漏，此为至关重要的操作前提。