Electronically Dimmable Aircraft Windows
How do you block the light of the sun?
That was the challenge posed to Gentex by Boeing. Window shades typically do the job on an airplane, but they’re cumbersome to operate, expensive to maintain, and do little to reflect the hightech nature of today’s modern aircraft. They’re an analog technology holdover operating in the digital age.
Boeing wanted a light management system that kept pace with the sophistication of its next generation of airplane. Plus, they wanted the windows to be bigger and the passengers still to be able to see out and enjoy the passing scenery. The solution was sophisticated and elegant – one that has received a positive reaction from passengers and aircraft manufacturers alike. Electronically dimmable windows.
Electrochromic (Dimmable) Mirrors
Gentex brought more than 30 years of experience in successfully dealing with glare. The company is the market leader in automatic-dimming mirrors for automobiles, with more than 200 million electrochromic devices (EC) in the field. These mirrors detect the glare from rearward-approaching vehicles and automatically darken to the precise level necessary to protect driver vision. Gentex produces more than 36 million EC devices annually for automakers throughout the world.
“The technology for airplane windows that darken is fundamentally the same as that for rearview mirrors,” said a Gentex spokesperson. “Our interactive window systems use a similar electrochromic formulation to the one used in the proprietary electrochromic technology that Gentex developed for autodimming automotive rear-view mirrors, using time-tested chemistry and durable device construction.”
However, for mirrors, in their completely darkened state, all but 4-5% of the light is blocked. The latest-generation dimming window for aviation allows less than 0.001% light transmission – 4 orders of magnitude darker. While the concept was the same, it had to be tailored specific to aerospace. The transparent conditions were different. The processes, the glass thickness, the design parameters, the chemistry were very different. They had to be developed. Re-invented. To date the R&D effort behind the electrochemically dimmable windows (EDW) for aerospace has generated more than 300 patents.
How It Works
Electrochromic technology uses electricity to change the color and light transmission of a transparent medium containing materials that are capable of generating color. This medium is typically sandwiched between two thin transparent layers that have transparent conductive coatings on the side that comes into contact with the medium. In this case, it is an electronic gel medium sandwiched between two thin glass panels. An electric current is passed through the conductive coatings and across the glass panels to cause an electrochemical reaction to occur in the gel. Applying a small electrical DC voltage across the gel causes it to darken, while removing the voltage allows the gel to return to its natural, transparent state. The voltage can be precisely controlled and adjusted in small increments to allow for the selection of intermediate states of light transmittance. Today there are more than 50,000 of these windows in airplane applications.
The windows automatically default to clear whenever the plane is parked, an important safety consideration. Dimming of all the windows can be controlled by the crew via the onboard network to allow for flight crew override and continuous monitoring of system performance. The transmission of ultraviolet and infrared radiation can be greatly reduced, lowering the heat load inside the cabin and enhancing the operating efficiency of the aircraft’s heating, ventilation and air conditioning systems. No more need to send a flight attendant down the aisle closing the shades to keep the plane cool as it sits baking in the sun.
The Gentex aircraft windows are relatively lightweight and self-contained with no moving parts, making them easy to maintain. An electronically dimmable panel is installed between the inboard dust cover and outboard structural cabin window. A Gentex designed and manufactured window-seat controller allows the passenger to activate the system and change the amount of visible light entering the cabin. They can opt to maximize it, minimize it, or select an intermediate setting. Passengers see only a stylish window and control button.
Latest Generation Window
The eye sees response time differently depending on altitude, a fact derived from numerous studies on vehicle safety. This phenomenon creates some issues when viewing the electrochromic dimmable window in a laboratory setting. As part of the development process, they designed a test lab that recreated the power of sunlight at various altitudes. Off the shelf test equipment for this sort of project does not exist, so it had to be invented. This enabled Gentex to explore what could be done to adjust the tinting qualities of the window.
In an airplane at altitude, the Gentex EDW dims quickly. The first-generation window went from full sun to zero in 60 seconds. Today, the third generation can accomplish the transition in 15 seconds. That equates to 0.001% darkness – 100 times darker than the Gen One windows – while still providing high optical clarity and great dynamic range compared to other approaches.
By applying their expertise in precision glass production, Gentex was able to develop thinner and thinner glass substrates, taking the thickness from .99 mm in the first versions to .70 mm today, while maintaining optical acuity. That equates to lighter weight, which contributes to fuel efficiency. A high level of vertical integration also provides the company with control over the quality of its glass, software, engineering and manufacturing processes.
Gentex expects future enhancements to include curved electrochromic dimming windows that allow for greater design flexibility and integration into a wider variety of cabin types with larger window openings. It also foresees wireless EDW control from smart phones and even EDW’s powered by solar energy.
This article was written by Dave Driscoll, Senior Aerospace Program Manager, Gentex (Zeeland, MI). For more information, Click Here .