How Smart Windows Work

By: Kevin Bonsor

Competing Technologies

Photo courtesy Robert Voets/FOX

There are several technologies that can be used in a smart-window application:

  • Thermotropics
  • Photocromics or photochromatics
  • Liquid Crystals
  • Suspended Partical Displays
  • Electrochromics
  • Reflective Hydrides

Cleaning window treatments can be a hassle. In this regard, smart windows are an easy alternative -- no more blinds to clean, or expensive drapery to be professionally cared for. Not only will smart windows cut down on your dry-cleaning bill, but they can save money on your power bill, too. When the summer sun is bathing your house in rays, things can really heat up inside your home, making your air conditioning work overtime. Smart windows can be used to block that extra heat. By blocking UV radiation, smart windows can protect paintings and furnishings in your home or office, too.


Control the level of light by increasing or decreasing the electricity flowing to the window. Slide the red button down to decrease the amount of electricity.

Although thermotropic and photochromic technology can be used in smart windows, both applications are ultimately impractical as energy saving devices because they cannot be manually controlled. Photochromic technology is most commonly used in sunglasses: Photochromatic material darkens in response to direct sunlight. As you can imagine, windows featuring this technology would not be entirely energy-efficient during cold winter months. On a cold but sunny day, instead of letting light in to warm a room, the windows would automatically darken instead. Thermotropic material responds to heat. So, on a beautiful, sunny summer's day, your view outside would be unavoidably diminished.

The other technologies are vying for a share of the estimated 20 billion square feet of flat glass produced worldwide each year. Currently, liquid crystals suspended particle devices (SPDs) and electrochromics are being touted as the latest and greatest window technologies -- with reflective hydrides nipping closely at their heels.

Let's take a closer look at SPD technology.