Glasses with transitional lenses are a neat idea in theory, but they have some shortcomings in practice. That's why researchers from the Georgia Institute of Technology are developing an alternative – clear eyeglasses that can be manually tinted into sunglasses, by the user.

The photochromic lenses in transitional glasses contain silver halide molecules that temporarily change shape when exposed to ultraviolet light. This causes the lens to darken, and some of that light to be blocked.

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One of the problems with them, however, is that the transition from clear to tinted can often take up to a few minutes. When you're performing activities such as driving or even flying a plane, that's simply not fast enough. Additionally, they won't tint if you're in a shaded place – such as the inside of a car – looking out onto a brightly-sunlit area.

By contrast, users of the Georgia Tech glasses can tint and un-tint them whenever and wherever they want, just by flipping a power switch.

The lenses contain electrochromic polymers, which respond to electrical current instead of ultraviolet light. In the prototype glasses, a mix of cyan, yellow, orange and blue polymers was used to create a brown tint, that blocks up to 70 percent of incoming light within a few seconds. By changing the ratios of the polymer colors, however, other colors of tints could also be achieved.

According to the research team, which was led by Anna Österholm, the inkjet printing/blade-coating technique used to create the lenses could easily be scaled up for commercial production. In fact, New Jersey-based startup Ashwin-Ushas is currently developing electrochromic sunglasses of its own, that use a photodetector to automatically adjust the level of tinting.

A paper on the Georgia Tech research was recently published in the journal ACS Applied Materials & Interfaces.

Source: American Chemical Society