No major window manufacturer's product line currently includes SPD-Smart Glass technology, which allows users to control light - and therefore heat - transmittal through windows. But SPD-Smart developer Research Frontiers Inc. in Woodbury, N.Y., has licensed a handful of companies to distribute SPD-Smart windows, whether they make the windows, work with manufacturers or apply the SPD film to off-the-shelf windows.

SPD stands for suspended particle device. Electrical particles suspended in a thin, flexible film applied to glass (or plastic) can receive commands - sensor/automatic or push-button - to control how much light passes through the glass.

In the off position, the particles align randomly to reflect and absorb light, darkening the glass. Applying an electric current realigns the particles and allows light to pass through clear glass.

Builder Scott Fisher of NuWest Custom Homes in Denver worked with Sierra Pacific Windows in Red Bluff, Calif., and SPD Systems in Plantation, Fla., an SPD-Smart licensee, to create windows that control light and privacy in the bathroom of a $1.15 million Parade of Homes show home. Had product not been donated, Fisher estimates his costs would have been $1,000 a window.

SPD-Smart licensee Razor's Edge Technologies in Lewes, Del., offers new construction windows, skylights, atriums and interior partitions nationwide through www.razorsedgetech.com.

Innovative Glass (www.innovativeglasscorp.com), a licensee in Jericho, N.Y., that sells windows, doors and skylights on the Eastern Sea-board, has a new skylight featuring a sensor that darkens the glass when the sun is directly above to prevent excess heat gain when no one is home.

For information on other SPD-Smart licensees and to view a demonstration of the technology, go to Research Frontiers' Web site at www.smartglass.com.