The Economist points out one of the paradoxes of energy efficiency:

Solid-state lamps, which use souped-up versions of the light-emitting diodes that shine from the faces of digital clocks and flash irritatingly on the front panels of audio and video equipment, will indeed make lighting better. But precedent suggests that this will serve merely to increase the demand for light. The consequence may not be just more light for the same amount of energy, but an actual increase in energy consumption, rather than the decrease hoped for by those promoting new forms of lighting.

The light perceived by the human eye is measured in units called lumen-hours. This is about the amount produced by burning a candle for an hour. In 1700 a typical Briton consumed 580 lumen-hours in the course of a year, from candles, wood and oil. Today, burning electric lights, he uses about 46 megalumen-hours—almost 100,000 times as much. Better technology has stimulated demand, resulting in more energy being purchased for conversion into light.

This phenomenon is known as the rebound effect or Jevon’s paradox. Saving the environment is not as easy as it seems.

Source: Marc Roberts Cartoons