General Aviation Research

Testing LED Lamps for Airport Runways

Problem:

The runway threshold lights used at most commercial airports are incandescent lamps that are inefficient and must be replaced often, a waste of energy and money.

Solution:

At two major airports, researchers from Embry-Riddle's Prescott, Arizona, campus are field-testing an alternative technology -- specially designed light-emitting diode (LED) lamps similar to those used in highway traffic signals. Their project is funded by the Federal Aviation Administration.

The green lights that guide pilots during the approach phase of flight to the end of runways are 300-watt incandescent lamps spaced 10 feet apart. A string of 18 lights across the end of a typical runway draws about 45 amps of current at full intensity, a significant use of power.

The lamps are very inefficient, however, converting only about 20 percent of their electrical energy into light.

The fixtures, which deliver white light, are covered by glass filters to produce the standard green color that pilots expect. These filters, however, eliminate about 80 percent of the lamps' illumination.

Thus, with only 20-percent lamp efficiency and 20-percent filter efficiency, a mere 4 percent of the electrical power is transformed into green light.

The lamps are operated at 50, 75 and 120 volts in three settings, low, medium and high, depending on the airport. At Sky Harbor, in Phoenix, Arizona (PHX), for example, the high intensity setting is used only a few hours a year, while at Grand Forks, N.D. (GFK), weather conditions require more frequent use of the high illumination.

The Embry-Riddle researchers are measuring the illumination, power consumption, and other characteristics of LED lamps that have replaced the existing runway threshold lamps at the Grand Forks and Sky Harbor airports. They'll also monitor the lamps' visibility to flight crews and how well they hold up to extreme temperatures, precipitation, jet blast vibrations, and other environmental effects.

Stephen Kahne, Embry-Riddle professor of electrical engineering at Prescott, leads the research team. The other investigators are Nick Manderfield, assistant professor of aeronautical science at the Prescott campus, and Tom Zeidlik, assistant professor of aviation at the University of North Dakota.

According to Kahne, LED lamps require substantially less electricity to produce light than do incandescent lamps. "And because they generate green light without filters," he says, "the inefficiency of filtering is also eliminated."

 

The experimental lamps at the Grand Forks and Phoenix airports, produced for the FAA by Lighting Innovations, a research company, use only 25 percent of the power required by incandescent runway lamps to produce the same illumination.

They also have lens heaters for cold weather use, which consume as much power as the LEDs themselves. But with the heaters turned on, the LED lamps are still twice as efficient as the existing lamps. When they're not in use, as is likely in Phoenix, efficiency is four times greater than the incandescent lamps.

"This demonstration is one of many attempts to make airport lighting less expensive without reducing its effectiveness," says Kahne, who speculates his study could show the new lamps cutting energy costs by a factor of three to four. "It's likely that in the distant future it will be hard to find non-LED illumination anywhere in airports."