Bill Browning of the Rocky Mountain Institute estimates that buildings account for more than one-third of U.S. electric power demand. More than one-fourth of that energy goes into lighting.

You don't need to be the brightest bulb on the tree to realize that energy-efficient lights, architectures that make better use of daylight and sensible approaches overall (like homes and offices that are smart enough to turn off the lights when the occupants leave) could reduce consumption enormously. Incandescent bulbs, once a bright idea, are obsolete yet still in heavy use. They are horribly wasteful: 90 percent of the electricity they draw goes out as heat rather than light. Compact fluorescent lights that fit standard sockets are four times as efficient and last 12 times as long. Efficiencies and savings with the use of new light-emitting diode technologies are likely to be even greater (see "LEDs Light the Future," TR September/October 2000).