The continued energy reduction promised by LED light sources in the US is dependent upon which electrical infrastructure the Federal Aviation Administration (FAA) selects from a range of rival options.
One of them is currently being trialled at Orlando International Airport (OIA) in Florida. Engineering consultancy AVCON has, according to founding principal Jim Kriss, had a range of engagements with Orlando for more than 20 years, including the pioneering installation of LEDs in 2004.
In 2010, the firm went on to implement power management technology from ADB Airfield Solutions, with an array of 120 centreline fixtures on taxiway Foxtrot, circuit TFC1.
The real challenge with LEDs, explains AVCON's senior aviation lighting specialist Carl Johnson, has been to derive the full energy reduction benefit from an airport's existing series circuit power system.
"While you gain energy efficiency with the LED because the electrical load is less for the same light output, you still don't realise all the efficiencies that the LED is capable of giving you," says Johnson. "There are currently four or five manufacturers - including ADB, Safegate Group and Crouse-Hinds - that went out and designed prototype power systems using different technologies."
The ADB advanced power supply (APS) system basically comprises a ratio transformer with two surge protectors, a bridge rectifier and the LED. Electronics are needed in the current generation of LED fixtures so that they can operate on the legacy electrical infrastructure, which uses a constant current regulator (CCR). The CCR is replaced with an APS that feeds the LED through a 2A alternating pulse width modulation (PWM) power supply.
LEDs: the cost savings
Johnson has no doubt about the overall savings available in the conversion of runway lighting from incandescent to LED. Lamp life rises from 1,000-1,500 hours at the maximum input current of a quartz halogen bulb to 50,000 hours, depending upon manufacturers' claims.
"In 1989, when taxiway Foxtrot was constructed, the incandescent lighting used 13kVA of energy and in 2004 the first generation of LED fixtures used 8.6kVA of energy, but with ADB's APS system energy usage is just 1.4kVA," he says. "So energy usage is 11% of what it was just 13 years ago."
The fixtures are constructed to FAA standard, which means that there are no issues around differently sized fixtures. "The physical mating to the light base is the same, no matter which fixture you get," Johnson explains. "The prototype fixtures come with the same 11.25in bolt circle. You take the old fixture off, unplug it, plug in the new fixture and then you bolt it down."
LED usage restrictions
The FAA, however, is insisting that, due to the difference in perceived colour and/or brightness, incandescent and LED lighting cannot be interspersed on runways, taxiways and aprons. Each section has to be uniform. The FAA is reviewing the use of LEDs on some airfield lighting applications that rely on an infrared signature. But LED fixtures may not provide sufficient infrared energy so, for this reason, LED obstruction, approach and high-intensity runway edge lights are not eligible at this time.
One key challenge for US civil airports wishing to change over to LEDs, says Johnson, is that at present such a move will need to be part of programmed upgrades and rehabilitation. This is in part because the FAA funds civil airport lighting and, particularly in the current economic climate, does not have a bottomless wallet.
When OIA installed the ADB APS, it used the same conduit, cable connectors and light bases. "In the vault, we took out the regulator that was feeding the existing lights and put the ADB APS in its place," he recalls. "This is considerably smaller, about 20% the size of a standard CCR."
In future, Johnson points out, vaults are going to shrink. "Instead of having a 50×100ft vault building, you might be able to get by with one that is 10×20ft," he says. "The air-conditioning and building lighting energy requirements are going to go down, and so is the cost of the building, along with a decrease in the size of the electrical service. So there will be a considerable saving on the initial investment.
Integration with circuit infrastructure
"From my perspective, being an airfield lighting designer, if it is in any way possible within the constraints of the project, I'm going to design my clients' projects using LED fixtures," he continues. "Whether it's a small general aviation field or a big international airport, when it is permissible, I'm going to design with LEDs. For the time being, they will have to be built into the standard series circuit infrastructure that has been around for years.
"Once the FAA selects the one or two new infrastructures that they are going to implement, we will have to look at individual cases and, as the airports and funding come up, choose which one to go with for a particular client. We will have to evaluate what their needs are."
Johnson concludes: "The FAA has done a pretty good job of writing the specifications for its fixtures," he says, "so that, no matter which manufacturer is providing the lighting, they will all have to meet the same FAA criteria. This means that when a contractor bids for a job, he bids for it with the manufacturer and knows that the fixture will meet FAA criteria."