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Buildings and Cities

Smart Glass

Electrochromic glass responds to different times of the day from two facings of a building. When tinted, the glass is reducing solar radiation and workplace glare, as well as the air-conditioning load, while maintaining daylight illumination inside. Sensors and even real-time weather data will override settings for daytime and allow more incoming light. The building is programmed by algorithms to respond to seasonal shifts in temperature and light; however, single panes of glass can be controlled from a smartphone at the user’s desk to adjust glare, light, and tint.

A one-time luxury, glass windows are now standard across the world, bringing light and visibility into the built environment without inviting in the weather. Except windows do let in the weather, in the form of heat or cold. They are much less efficient than insulated walls at keeping room temperature in and outside temperature out—by a factor of ten or more.

Various measures can improve a window’s efficiency: layered panes, reflective low-emissivity coatings, insulating gas between panes, and tightly sealed frames. More adaptive technologies, dubbed “smart glass,” make windows responsive in real time to sunlight and weather, reducing a building’s energy load for lighting and improving heating and cooling efficiency.

Smart glass relies on chromism, the term for any process that causes material to change color. Electricity triggers it in electrochromic glass: When exposed to a brief burst of voltage, ions move into another layer of glass and the tint and reflectiveness change. Thermochromic glass is triggered by heat: Based on outside temperature, it transitions automatically from transparent to opaque and back again. Photochromic windows operate similarly, on the basis of light exposure. Currently challenged by cost, smart glass will become much more common in the coming decades.


Roman glass: Deviren, A. Senem, and Phillip James Tabb. The Greening of Architecture: A Critical History and Survey of Contemporary Sustainable Architecture and Urban Design. Farnham, Surrey, UK: Ashgate Publishing Limited, 2013.

windows…less efficient insulated walls: Gunn, Dwyer. “This Sustainable New Tech Will Make You See Windows in a Whole New Light.” The Guardian. November 10, 2016.

most efficient windows…U-value: Energy Star. “ENERGY STAR Most Efficient.”

Electrochromic glass…developed in the 1970s and ’80s: “Researchers Develop ‘Smart’ Window to Cut Energy Consumption.” New York Times. September 29, 1992.

nanoscale metal oxides: Hickey, Shane. “Smart Glass Offers Window of Opportunity for View.” The Guardian. November 23, 2014.

disaggregate light and heat: Korgel, Brian A. “Materials Science: Composite for Smarter Windows.” Nature 500, no. 7462 (2013): 278-279.

Japan…[drop in] cooling loads: Yoshimura, Kazuki, Kazuki Tajima, and Yasusei Yamada. “Development of Switchable Mirror Glass.” Synthesiology 5, no. 4 (2013): 262-269.

electrochromic line…[vs.] traditional windows: Gunn, “Windows.”

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