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Smart Window Windows not only let light in to cut down an electricity use for lighting，but the light coming through the window also provides heat.However，windows are not something people typically associate with being a cutting edge1 technology.Researchers are now working on new technologies that enable a window to quickly change from clear to dark and anywhere in between with a flip of a switch2. It took us a long time to figure out what a window really is, says Claes Granqvist.Hes a professor of solid-state physics at Uppsala University in Sweden3.Its contact with the outside world.You have to have visual contact with the surrounding world to feel well. So，windows and natural light are important for improving the way people feel when theyre stuck indoors. Yet，windows are the weak link in a building when it comes to energy and temperature control.In the winter，cold air leaks in.When its hot and sunny，sunlight streams in.All of this sunlight carries lots of heat and energy.And all of this extra heat forces people to turn on their air conditioners.Producing blasts of cold air，which can feel so refreshing，actually suck up enormous amounts of electricity in buildings around the world. Windows have been a major focus of energy research for a long time. Over the years，scientists have come up with a variety of strategies for coating，glazing，and layering windows to make them more energy efficient.Smart windows go a step further.They use chromogenic technologies which involve changes of color. | 
