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The luminous efficacy (lumens/watt) of LEDs vary with color. Currently white LEDs are measuring between 20- 60 lm/W. This variance is subject to differences in chromaticity as well as wattage. The U.S. Department of Energy recently released a study that estimates efficacy to be 100 lms/W by 2010. By one estimate, replacing the incandescent traffic signals in the United States alone with LED signals would save nearly 2.5 billion kWh annually. Red traffic lights, for example, pay back their initial investment in 2.5 to 3 years through energy savings. Savings due to reduced maintenance are significant, and can be a leader in cost savings when replacement is difficult or expensive.
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