One of the most energy-efficient office buildings in the world is about to open in Golden. It's on the campus of the National Renewable Energy Laboratory or NREL. It can heat and cool itself without using much electricity at all. Computers will shut down themselves when they're not in use. And because of things like solar panels and wind turbines, NREL expects it to produce more energy than it uses. Another of the building's green features comes from a Denver start-up. Ravenbrick LLC is all about making windows smarter. It's developed a film which acts a lot like eye glasses that darken or lighten depending on the sun. Smart windows have been around for about 20 years, but they've always needed electricity to alternate from clear to tinted. The company estimates the technology will reduce a building's energy needs by 30 to 40 percent. Wil McCarthy is the co-inventor and speaks with Ryan Warner.