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Think of the particles suspended in Research Frontiers, Inc.'s (Woodbury, New York; www.refr-spd.com) SPD Smart Glass film as "nano blinds." In the presence of an electric current, they re-orient themselves to allow light to pass through glass or plastic. Turn the power off-the film draws just 0.65 watts/m2 when letting the maxi-mum amount of light through-and 99% of visible light is blocked. The particles are contained in a film, and the suspended particle device (SPD) film is applied with the same process used for making laminated glass. There is no limitation to the panel size as the film can be produced on wide-width coating machines.
"Currently, the greatest area of interest at both OEMs and suppliers," says Michael LaPointe, v.p. Marketing, Research Frontiers, "is for sunroof and glass roof systems." That's because the film eliminates the need for a separate sunshade system, and opens a greater percentage of the panel to viewing. "Some of the panels being planned are so large," says LaPointe, "that slide-across shades are becoming impractical, but the SPD film lets you reduce both weight and warranty concerns while reducing the load on the climate control system." It also works with radical designs because the film (it is currently bonded between single layers of glass or polycarbonate, though licensees of the technology are working on a single-layer design that places the film on the inner surface of the panel) conforms to the shape of the panel. Just don't expect it to be used across the windshield. Since the film defaults to dark when the power is off, it can't meet federal regulations on minimum light transmission levels. However, it can be placed along the upper border of the windshields to replace the painted-on sunshade currently used by most glass makers.
When asked about competing technologies, however, LaPointe is quick to dismiss them. "So far, electrochromic technology has only been able to offer binary transition states-that is, fully dark, fully clear, or pre-set transition levels between those two extremes. On a glass roof panel," he claims, "the transition time might take as long as 10 minutes." Liquid crystal film, on the other hand, is produced in a film process (manufacturers making LC film should have no problem with SPD film, claims LaPointe) but is more expensive per square foot, reacts more slowly, and can produce an "iris effect" that distorts the image in larger applications. The switching speed for a SPD film, on the other hand, is claimed to be a few seconds and consistent, no matter the size of the panel. Also, it has an infinite gradient, and can be changed through the use of a rheostat or an automatic light sensor. Not surprisingly, given the growth in the market penetration of electrochromic rear view mirrors, SPD is a strong consideration for this application, and similar technology is under investigation to replace today's sun visors with SPD film panels.