LED light bulbs have a slight environmental edge on compact fluorescent bulbs and both trump traditional incandescent bulbs by a wide margin, the Pacific Northwest National Laboratory says in a new report.

PNNL, a U.S. Department of Energy lab based in Richland, Wash., compared the environmental footprint of the three bulbs, including mining of raw materials, manufacturing, disposal and electricity use. It's the first public report to examine the impact of LED manufacturing in depth, the lab says.

Among the study's conclusions:

* Both LEDs and CFLs are substantially more environmentally friendly than traditional incandescents, which consume far more electricity -- the dominant environmental impact. Switching away from incandescents reduces the environmental harm of lighting by three to 10 times.

* Today's LED bulbs cause slightly less environmental harm than compact fluorescents in 14 of 15 areas studied. Those areas include global warming potential, land use and pollution of water, soil and air.

* The LED bulb's main environmental drawback is its use of an aluminum "heat sink" at the bottom of the bulb. That's because mining and processing aluminum is energy intensive and generates sulfuric acid and other hazardous byproducts.

* By 2017, LED bulbs will have half the impact of today's LED bulbs and 70 percent less impact than today's CFLs, which are not expected to change significantly. LED bulbs will become more efficient, for example, reducing energy use and cutting the heat generated and the required size of heat sinks.

Next, lab researchers will study the amount of hazardous materials in the three types of bulbs -- mercury in CFLs, for example -- and whether they exceed federal and California disposal regulations.

Energy Star, the federal government's program to certify energy efficient products, warns that LED bulb quality can be spotty and some manufacturers make exaggerated claims. Energy Star's light bulb page includes a list of LED and CFL bulbs that meet its quality standards.