Windows play a key role when it comes to saving energy. The principle loss of energy in buildings is through windows: A pane of glass can lose or gain up to 10 times the amount of heat than a same sized wall space. Smart windows are changing that. On sunny days, they automatically tint to block heat and glare; on overcast days, the tint adjusts to a lesser level. This process reduces the energy consumption of the building by up to 20 percent. There’s also evidence that suggests that the biological effects of increased exposure to natural light increase worker productivity by up to 2 percent.