Colorimetric analysis and color rendering performance of a small-scale glazing system with thin monolithic aerogel in the interspace

Transparent surfaces in buildings ensure natural light into indoor spaces and allow energy saving, reducing consumptions for artificial light, and the occupants’ psychophysical well-being. For this reason, color rendering lit by the natural light entering the windows is a major concern. However glazing surfaces represent a weak point for the building envelope, due to poor thermal and acoustic performance. Monolithic aerogel constitutes a promising transparent solution, able to guarantee excellent thermal and acoustic properties, together with remarkable optical performance. In the perspective, this paper focuses on the analysis of the optical properties and the color rendering performance of a small-scale prototype consisting of float glass-monolithic aerogel-float glass. The aerogel inner pane, 3-mm-thick, was prepared using a rapid supercritical extraction method developed at the Union College Aerogel Lab. Optical measurements carried out using a conventional spectrophotometer with a small integrating sphere in the 250-2500 nm wavelength range, indicate high transmittance in the visible part of the spectrum. As concerns color rendering, an original measurement methodology based on material transmission spectra was developed through the use of chromatic distortions verified on an experimental basis. Although the traditional calculation procedure for transparent components considers the color rendering of the object illuminated by the light transmitted through the element, the explained one involves the evaluation of the color observed through the transparent material. The effect of the glazing system with aerogel on color rendering was assessed by means of a dome-shape illuminator, a chromameter, and a color-checker as a reference for the colors. The RGB and CIE Lab coordinates of the test color samples of the color-checker with and without the aerogel were used to calculate the color shift. The results showed that the glazing system tends to make the colors brighter and to move them towards blue hues. Then a new color rendering index, identified as R_(a,p) (proposed Color Rendering Index), was calculated. Finally for the innovative glazing system also the Color Rendering Index R_a in accordance to EN ISO 410 was evaluated, to compare the results of the two procedures.