Describes how windows can be made transparent or opaque at the flick of a switch.
Photo: Electrochromic glass changes color under electric control: Left: Here it's transparent and looks much like ordinary glass; Right: Apply a small voltage and it turns opaque (blueish and dark). Photos by Warren Gretz courtesy of US Department of Energy/National Renewable Energy Laboratory (DOE/NREL) . Since the early 20th century, people have got used to the idea of buildings that are increasingly automated. We have electric clothes washing machines , dishwashers , vacuum cleaners and much more. So why not fit our homes with electric windows that can change from clear to dark automatically? Smart windows (also referred to by the names smart glass, switchable windows, and dynamic windows) do exactly that using a scientific idea called electrochromism, in which materials change color (or switch from transparent to opaque) when you apply an electrical voltage across them. Typically smart windows start off a blueish color and gradually (over a few minutes) turn transparent when the electric current passes through them. Glass is an amazing material and our buildings would be dark, dingy, cold, and damp without it. But it has its drawbacks too. It lets in light and heat even when you don't want it to. On a blinding summer's day, the more heat ("solar gain") that enters your building the more you'll need to use your air-conditioning —a horrible waste of energy that costs you money and harms the environment. That's why most of the windows in homes and offices are fitted with curtains or blinds. If you're into interior design and remodeling, you might think furnishings like this are neat and attractive—but in cold, practical, scientific terms they're a nuisance. Let's be honest about this: curtains and blinds are a technological kludge to make up for glass's big, built-in drawback: it's transparent (or translucent) even when you don't want it to be. Photo: Forget the curtains, forget the blinds! "Smart windows" made from electrochromic glass turn from clear to…