A team of researchers from the University of Notre Dame has developed a new window coating that blocks heat-generating ultraviolet (UV) and infrared light, while letting through visible light, no matter the sun's angle.

Capable of being incorporated onto existing windows or automobiles and subsequently reducing the costs associated with air-conditioning by more than one-third in hot climates, the coating also maintains its efficiency despite the sun’s position in the sky.

Researchers at the University of Notre Dame have developed a new window coating to block heat-generating ultraviolet and infrared light and allow for visible light, regardless of the sun's angle. Source: University of Notre Dame

This coating, according to the researchers, unlike currently available window coatings optimized for light entering a room at a 90° angle, was developed with the understanding that the angle between the sunshine and a window is always changing.

As such, the researchers created a transparent window coating by stacking ultra-thin layers of silica, alumina and titanium oxide on a glass base while a micrometer-thick silicon polymer was also added to enhance the coating’s cooling power, which reflects thermal radiation through the atmospheric window and into outer space.

To ensure the coating could accommodate multiple angles of solar light, the researchers shuffled the layers into an optimal configuration that both maximized the transmission of visible light and minimized the passage of heat-producing wavelengths. To accomplish this, the researchers used quantum annealing, which is an optimization process for identifying the global minimum of a given objective function over a given set of candidate solutions, via a process using quantum fluctuations.

The researchers found that the coating maintained transparency and reduced temperatures by 5.4° C to 7.2° C in a model room during a series of trials, even when light was transmitted in a series of angles.

"Like polarized sunglasses, our coating lessens the intensity of incoming light, but unlike sunglasses, our coating remains clear and effective even when you tilt it at different angles," the researchers explained.

The research is detailed in the article, “Wide-angle spectral filter for energy-saving windows designed by quantum annealing-enhanced active learning,” which appears in the journal Cell Reports Physical Science.