Engineers are always plugging away to get better energy efficiency out of our products -- like cars that guzzle less gas or light bulbs that burn brighter on fewer watts. But even if we replaced all today's bulbs with energy-sipping LEDs, the world might not see any energy savings, according to a study in the Journal of Physics D. Because the more efficient lights get, the more light we tend to use.

The researchers looked at light consumption since the year 1700. Even though today's compact fluorescents are 500 times more efficient than candles and whale oil lamps, what we spend on overall lighting hasn't gone down. It's just increased proportionately to our wealth. For the past 300 years we've consistently spent just about seven-tenths-of-one-percent of our gross domestic product on artificial lighting. And the researchers think this trend could continue, because many parts of the world still haven't satisfied their appetite for light.

The upside is, more lighting means more productivity. But if the goal is green living, LEDs may not be a stand-alone solution. Instead, the authors suggest coupling those LEDs with energy policies that encourage smart lighting use. Now that's a bright idea.