Lighting accounts for a whopping 15 percent of a household's electricity and significantly contributes to greenhouse gas emissions. Without even flipping a switch, you can start reducing your impact. Take advantage of natural light by moving furniture closer to windows and opening curtains during the day. If you haven't already, switch to compact florescent light bulbs (CFLs), which use 75 percent less energy and last 10 times longer than incandescents (you'll also save $30 over the life of each bulb). Install task lighting —such as under-counter kitchen lights —and EnergyStar-qualified fixtures to reduce even more energy.