If you're going to do just one thing for the planet, make it the switch to compact fluorescent light bulbs (CFLs).  Although they cost several times more upfront than regular incandescent light bulbs, they also last about 10 times longer, which means that for every CFL you screw in, you'll be saving eight incandescent light bulbs from landfill purgatory. Plus, you'll save some serious cash in the long run. Because CFLs use 75 percent less energy, swapping one incandescent bulb for a CFL reduces carbon dioxide by 500 pounds a year; replacing 17 has the equivalent effect of taking one car off the road for a year. Just remember to recycle spent bulbs responsibly - CFLs contain trace amounts of mercury, which although isn't enough to be hazardous to you, could pose a problem in landfills when mercury from multiple bulbs leaches into the ground.