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Low-cost, 'tunable' window tintings make blinds redundant

11 June 2015

Technology developed by the University of Cincinnati (UC) and industry partners can do something that neither blinds nor existing smart windows can do.

Window tinting can turn milky for privacy while still allowing 90 percent or more of sunlight to enter (image courtesy of Tim Zarki, University of Cincinnati)

A partnership between the University of Cincinnati, Hewlett Packard, and EMD/Merck Research Labs has resulted in a patent-pending breakthrough in 'tunable' window tintings. Traditional window shades could soon be replaced by a low-cost tinting where the brightness, colour temperature (warm or cool just like incandescent light bulbs) and opacity (privacy) are adjustable by the user.

The research, described in the journal, Applied Optics, was led by Sayantika Mukherjee, a doctoral student in UC's Novel Devices Laboratory.

Importantly, the newly developed device structure that makes these 'smart windows' possible is very simple to manufacture, allowing affordability for both business and home use. It can be integrated into new windows or applied to existing windows, by means of a roll-on coating consisting of a honeycomb of electrodes.

Mechanical shades to provide privacy and to block light is inexpensive and effective, which has slowed the adoption of electronically controlled window tinting, which previously could only mimic the clear-to-opaque performance of mechanical shades. However, this new breakthrough at the University of Cincinnati is about to change that.

"Simple electronic window switching is not enough," says UC's Professor Jason Heikenfeld. "You need to provide consumers with something you can't do mechanically, and for which there is already a large demand. For example, there is already proven demand for control of colour temperature in the lightbulb market, and after all, windows are a source of lighting.

"Maybe even more compelling, go home to your neighborhood and look at the drawn blinds for privacy but which also block sunlight. What if you could have your privacy and also let the light in at any brightness you want?"

Shade and privacy can thus be simultaneously, electronically controlled for the first time. Windows could go milky for privacy so no one can see in, but still allow 90 percent (or more) of the available light in. Or, a setting change could dim the entering light or change the colour of the light along a spectrum from cooler blue to warmer yellow.

Heikenfeld and UC's Novel Devices Laboratory are international leaders in developments related to adaptive optics, e-paper and the use of colour in displays on electronic devices, and have made breakthroughs related to the brightness, colour saturation and speed of such displays.

The challenge for the UC, Merck and HP team consisted of applying this technology to a larger surface like windows, and to do so in a way that could be manufactured inexpensively, for less than the $30 per square foot.

"Basically, one colour has one charge. Another colour has another charge, and we apply voltage to repel or attract the colours into different positions," Mukherjee explains. "The basic technology is not that different from what our group has previously demonstrated before in electronic display devices.

"The greater challenge was to find an appropriate device structure in order to apply the technology to the larger surface area of a window in a way that was inexpensive and fairly easy. The greater impact for us was to realise the potential of a few selective but compelling operating modes such as changing colour temperature or privacy/shade."

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