Optical fiber sensor solutions for in-situ transmittance control of electrochromic glazing

Windows are essential to let natural daylight into our buildings. Smart and dynamic glazing is an important technology for achieving sustainable and energy-efficient buildings with good indoor environment by reducing the need for air-conditioning. Electrochromic glazing is the commercial state-of-the-art for smart and dynamic glazing. In principle electrochromic glazing works like a thin film battery, whose lifetime is enhanced if the combination of elevated temperature and a high state-of-charge, or low light transmittance, are avoided. Therefore, a direct transmittance measurement is desirable. In this study, we have evaluated four different methods using optical fibers, whereof two methods were found to work well, both in initial testing and when compared to reference transmittance cycling measurements. Both methods relied on light from a light emitting diode, at 810 nm wavelength, that was propagated either through the electrochromic foil or along it. The latter shows most potential to be implemented in a manufacturing process of smart glazing. • In-situ transmittance measurements of electrochromic glazing enhance lifetime. • Description and tests of four different methods of in-situ transmittance measurements. • The active configuration using 800 nm was found to be least distorted by external light. • Clear correlation of two methods compared to reference transmittance measurements. • Measuring along the foil was found to be feasible for manufacturing but requires further studies for understanding.