Researchers at Purdue University say they have developed a new breed of LED, or light-emitting diode, that could eventually replace incandescent and fluorescent light bulbs and cut overall energy consumption in countries such as the U.S. by 10 percent. LEDs, which currently require an expensive sapphire base to function, are already common in stoplights, flashlights, and electronics. A form of so-called “solid-state lighting” — meaning they are semiconductor devices that emit light when electricity is applied — LEDs are four times more efficient than incandescent bulbs, do not contain the harmful mercury found in fluorescent bulbs, and can last as long as 15 years before burning out. Their expense, however, has been prohibitive. But the Purdue engineers report in the journal Applied Physics Letters that they have dramatically reduced the cost of LEDs by making them on low-cost, metal-coated silicon wafers instead of on a sapphire base. “The LED technology has the potential of replacing all incandescent and compact fluorescent bulbs, which would have dramatic energy and environmental ramifications,” said the lead Purdue researcher.