Improving dimmable windows for aircraft

An alternative to the old-fashioned window shade could be coming to a passenger seat near you. The developers of new, easier-to-install electronically dimmable windows are talking to airlines about the possibility of adding the windows during their planned aircraft refurbishments.

Older versions of the windows, first developed in 2001, haven’t caught on with commercial airlines. Caution had to be taken in the design and installation to keep a passenger’s earring or coat zipper from scratching the polycarbonate surface layer of the dimmable glass laminate. Given the laminate’s expense, aircraft manufacturers had to install it behind an additional layer known as a “scratch lens” or “dust cover” — also made of clear polycarbonate plastic, but cheaper to replace if damaged.

Now, Research Frontiers of Woodbury, New York, has figured out how to combine its dimmable technology with chemically strengthened glass like that in smartphone screens. The modified technology was first certified by the FAA in 2019 for Epic’s E1000s, a turboprop design promising “jet-class performance.” The dimmable laminate, called SPD-Smart for the digitally controlled suspended particles in the material, no longer must be protected by a scratch lens. That means installing the new version of the dimmable windows is easier and less expensive than the polycarbonate-surfaced version, especially in retrofits. The new dimmable glass also saves weight and cabin space compared to the multilayered installation required for the polycarbonate version, and the new glass is clearer optically.

Just as with the original design, the updated technology consists of a dimmable film laminated between two layers of clear plastic or glass, depending on the version, each coated on the inside with an electrically conductive material, such as indium tin oxide. Applying voltage to the film via this conductive material causes disc-shaped polyiodide nanoparticles to align like open window blinds to permit a desired amount of light to shine in. These nanoparticles are suspended in microscopic droplets of a proprietary liquid within the film. The more voltage applied, the greater the alignment and the more light passes through. Turning the current off entirely prompts the nanoparticles to revert to their random positioning and effectively block all light.

The technology provides more precise shading than standard window shades — passengers could partially or completely dim their individual windows with a dial, or airplane crew members could dim one entire side of the plane’s windows to block sunlight on a red-eye flight or during an in-flight movie, said Michael LaPointe, vice president for aerospace products at Research Frontiers. The windows also provide better thermal and acoustic insulation, better protection from infrared radiation and more savings on air conditioning than standard windows with shades, LaPointe said.

With the windows dark and blocking sunlight, airplanes that are sitting idle and empty of passengers would be less likely to have to run their AC units, for example. And the windows can switch from dark to clear in one second or be paired with photosensors to automatically dim when specific levels of sunlight hit the sensors.