by Paul Cianciolo, FAA Safety Briefing

LED lights — or light-emitting diodes — last longer, are more reliable, and use less electricity than the traditional incandescent bulbs. I personally started the switch to LED lights at home and, I admit, I took them with me last time I moved residences. LEDs are worth the investment.

Airport operators are also seeing the light in LED use. The surface of an airport is chock-full of lights, and each serves to enhance safety during times of reduced visibility. Lighting systems provide pilots with the visual cues to quickly and positively identify the runway environment. They also provide an extra margin of safety for approaching aircraft.

The introduction of LEDs on airports was primarily driven by cost, but efficiency and the environmental considerations of using less electricity is making them the light source of choice.

LEDs also offer some potential safety enhancements over traditional incandescent lights. For smaller general aviation (GA) airports, including privately owned and operated airfields, LEDs may enable the inclusion of safety enhancing lighting systems that would otherwise be cost prohibitive at smaller airfields.

Testing the Light

This conclusion did not come from some unicorn organization; it came from an academic, government, and industry partnership called PEGASAS. PEGASAS is the name given to the FAA’s Center of Excellence (COE) for General Aviation, which stands for the Partnership for the Enhancement of General Aviation Safety, Accessibility, and Sustainability. It is one of six active Air Transportation Centers of Excellence established by the FAA to create cost-sharing partnerships with academia and industry throughout the United States.

What distinguishes a COE from other research grant arrangements is that the core universities go through a vigorous competitive process to exist as a single, cooperating entity for a specific period. Every dollar of federal money awarded to the COE is matched one-to-one, resulting in a win-win relationship for the university researchers, as well as the American taxpayers.

Stretching Out the Light

One PEGASAS research project related to LEDs that has a great potential benefit to GA safety is the Linear LED Lighting Study. The project goal was to gain an understanding of the potential benefits of linear LED lighting systems — versus point source lights — for the spatial orientation of airfield users, including pilots and ground vehicle operators. Experimental field-testing arrangements of linear LED lighting systems happened at Ohio State University Airport (KOSU).

Traditionally, a point source lighting system is what we see on taxiways and runways today: the familiar “sea of dots.” Without a good airport diagram, a pilot could potentially make a turn between the lights where there may not be pavement. It is often difficult for pilots to recognize when a turn is coming up until they are essentially right up on it. With typical 50 foot or more spacing between the dots, and a white-light accidently turned on in the cockpit by a flying companion, there is potential for unwanted grass cutting.

Accurate visual perception on the airfield is important for safe and efficient operations. Information of this nature needs to be concise, simple, and discernible. With LEDs arranged in closely spaced configurations and, in this case, in a linear arrangement, the pilot will see a line rather than spaced dots. This project evaluated different configurations, e.g., different lengths of lines of LEDs, and measured the distance that pilots could accurately discern what the lights were indicating, such as a gentle left turn or a sharp right turn ahead.

Participants were exposed to a sampling of all conditions — 50 ft. and 150 ft. spacing, left and right turns, and 30 degree and 90 degree turns. The investigator recorded what type of lighting condition the participant reported seeing, as well as the time and distance from the lights at the time of the reaction. The use of linear source LED lighting to depict taxiway leadoff lighting on a runway resulted in improved visual recognition, as compared to point source lighting. The new LED strip-light proved to provide a safer airport surface area than a sea of glowing dots.

Energizing the Light

Another PEGASAS project studied different infrastructure concepts for how LED fixtures perform when installed on existing airport electrical systems. Since LEDs use less energy, have the potential for reduced maintenance on the lighting systems, and have the capability for non-traditional light fixtures — as in shapes like the linear lines of lights mentioned previously — it makes business sense to switch. However, the electrical requirements for traditional lighting systems are different from those using LEDs.

To accomplish this project goal, the PEGASAS team established three different field sites at Purdue University Airport (KLAF), which were outfitted with circuits that included LED fixtures. Each site was located at varying distances from a wireless data collection system. The tests included sending a command signal through the power cables to each of the LED fixtures. The commands tell the lights to change intensity — dim or get brighter. This type of field-testing can be used to validate models to understand the ability of LEDs to respond appropriately to signals sent through airport power circuits.

Since this project has closed, all operations have moved to Cape May Airport (KWWD) in New Jersey, where data collection will resume once the necessary equipment is installed.

Modelling the Light

The FAA is considering alternative circuit and control topologies — the arrangement of the various elements of a communication network — to provide power to LED-based runway lighting systems. Each of these new topologies introduce potential technical challenges.

Another PEGASAS project examined two primary topologies. One is vault-centric and the other is fixture-centric. Purdue University was tasked with creating a mathematical model that could run simulations of various electrical infrastructure configurations to address concerns.

In vault-centric topologies, each of the LED lights are connected to the system through a transformer. Within the fixture, a current transformer supplies a diode rectifier to power the LED. The electrical current through the system is controlled at the source located in a vault. The challenge is to ensure that each LED will receive the same current so that each creates the same level of brightness. The concern stems from the long distances of cable, which potentially eliminate the accuracy of a series-based model of LEDs. This is particularly a concern for regulating the system at low levels of electrical current.

In fixture-centric configurations, power-electronics are added at the LED itself to enable regulation of the individual LED current. A primary concern of this architecture is whether each LED will receive the same electrical current so that each LED achieves an equal level of illumination. Over the distances considered in this circuit, the cable-runs act as transmission line elements that create losses, which is a concern at low current levels.

Managing the flow of electricity is still a challenge when integrating LEDs into an airport lighting system. Both models have their pros and cons.

Being the Light

A Pegasus is not a unicorn, and PEGASAS is no ordinary team. If you were to bet on the safest “horse” to ride, the less pointy team player is the way to go. It is the FAA’s job to provide the safest, most efficient aerospace system in the world. And that is better accomplished through a partnership like PEGASAS. The LED projects are shedding light on ways that may enable small airfield operators to afford safety enhancing lighting systems.

In the not too distant future, you may even start to see that sea of dots stretched out to better guide you down the taxiway. Be assured that you are not taxiing at warp speed; you are witnessing the speed of progress through PEGASAS.

Paul Cianciolo is an associate editor and the social media lead for FAA Safety Briefing. He is a U.S. Air Force veteran, and a rated aircrew member and volunteer public affairs officer with Civil Air Patrol.