Reviewed by Frances BriggsJun 24 2025
Researchers have developed a new smart window technology to improve energy efficiency in buildings. This technology effectively eliminates glare from outside sources and enables users to control the amount of heat and light that enters through windows.
Image Credit: Mark B Pixels/Shutterstock.com
The research, published in ACS Energy Letters, could revolutionize building costs and energy use, as windows are a significant factor in heating and cooling energy loss in buildings.
The building sector accounts for roughly 40 % of global energy consumption, making improvements in energy efficiency critical in reducing the sector's environmental impact.
One area of focus is minimizing energy loss through windows. To address this, a research team at KAIST has developed a ‘pedestrian-friendly smart window’ technology that not only cuts heating and cooling costs in urban buildings but also helps reduce light pollution in cities.
Their technology is a reversible electrodeposition and electrochromic mirror (RECM), a next-generation smart window built on a single-structured electrochromic device. The RECM system regulates both near-infrared (heat) and visible light transmittance.
What sets RECM apart is its ability to reduce glare from external reflections using a carefully designed combination of electrochromic materials. Unlike conventional windows that passively react to ambient light and temperature, RECM operates in real-time through electrical impulses.
The RECM system created in this study has three modes based on voltage control:
- Mode I (Transparent Mode) permits sunlight to penetrate the indoor area as it transmits light and heat, similarly to regular glass.
- In Mode II (Colored Mode), a redox process produces Prussian Blue (PB) and DHV+• chemical species, resulting in a deep blue window. With this mode, light is absorbed, and just a fraction of the heat is transferred, providing privacy and indoor temperature control.
- Silver (Ag+) ions are reduced and deposited on the electrode surface in Mode III (Colored and Deposition Mode), reflecting heat and light. At the same time, the colored material blocks glare for pedestrians outside by absorbing the reflected light.
To evaluate its performance, the researchers tested the smart window on a miniature model house. Under identical sunlight exposure, the temperature inside a standard glass model rose to 58.7 °C within 45 minutes. In contrast, with the RECM operating in Mode III, the temperature peaked at just 31.5 °C—a 27.2 °C difference.
These results highlight RECM’s potential as a fast-response, electrically tunable solution. With its adaptive solar control, improved energy efficiency, and glare-reducing benefits for pedestrians, RECM stands out as a strong candidate for sustainable, smart urban infrastructure.
This research goes beyond existing smart window technologies limited to visible light control, presenting a truly smart window platform that comprehensively considers not only active indoor thermal control but also the visual safety of pedestrians. Various applications are anticipated, from urban buildings to vehicles and trains.
Hong Chul Moon, Professor and Study Corresponding Author, Korea Advanced Institute of Science & Technology
Journal Reference:
Jo, H. J., et al. (2025). Glare-Free, Energy-Efficient Smart Windows: A Pedestrian-Friendly System with Dynamically Tunable Light and Heat Regulation. ACS Energy Letters. doi.org/10.1021/acsenergylett.5c00637