Glazing that allows you to switch between transparency and translucence at the push of a button is prohibitively costly right now, but chromogenics research and competition may soon allow home owners to enjoy the energy-saving benefits of "smart windows."

"Switchable glass," also known as "smart windows" lets you control the level of transparency and a U.S. Department of Energy initiative is taking a close look at the technology's energy-saving qualities.

The special class of glass is scientifically known as chromogenics, glazing materials that selectively control the spectral aspect of radiation.

Electrochromics, which appears to be the most suitable chromogenic technology for energy control, is the subject of the most intensive research. Electrochromics employ materials that react to electric voltage.

When voltage is applied to liquid crystals, quartz and other materials sandwiched between sheets of glazing, the materials react by losing their visible qualities and become transparent.

Flip the switch off and the materials return to their original state, creating a tint, frost, or shade that reduces the passage of light.

Available in brand names Thermosee, SageGlass, Polyvision, ChromaFusion and others, the glazing systems can create open, inviting, transparent glass-walled spaces you can instantly transform into private areas.

Because the glazing offers darkening qualities, they also have a potential for energy-saving applications that could help offset the special glazing's high costs.

"Switchable glass can costs hundreds of dollars per square foot," said Lisa Gonzalez, president and CEO of Design Alternatives in Santa Clara.

Related technologies include:

  • Thermochromic materials changes optical properties in response to temperature changes. It mainly consists of liquids or gels sandwiched between layers of glazing. Thermochromic windows are designed to block solar gain. A drawback is that they reduce visible light transmission.
  • Photochromic materials change their properties in response to light. Photo gray sunglasses are the best known example. When photochromic materials change their transmittance, the absorptivity is increased, thus causing the glass to absorb more heat. On sunny cold days, they absorb solar heat and room source heat and then radiate some heat back to the surroundings. On sunny hot days, they do not reject as much solar heat as reflective windows.

"Picture a window as an appliance, one that makes you dramatically more comfortable, saves you energy and always allows you to enjoy the view," said Jay Schrankler, vice president of Honeywell Home Comfort Systems. The company recently teamed with SAGE Electronics to develop and introduce user-controlled window glass.

"This alliance uniquely combines the technical breakthroughs of SAGE's electronic window glass with Honeywell's recognized leadership in building control technologies. This combination of capabilities and shared vision has the potential to revolutionize the window industry," said SAGE founder and president John Van Dine.

Look for companies to test market "smart" windows this year.

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