Energy Equations

These LED bulbs are barely 1/5 inch (5mm) in diameter at the base. (GE)

Carroll McCormick explains how Light Emitting Diode technology is revolutionising energy and maintenance costs.

These LED bulbs are barely 1/5 inch (5mm) in diameter at the base. (GE)

In 2006 the Hartsfield-Jackson Atlanta International Airport and Columbus, Ohio-based manufacturer ADB Airfield Solutions conducted a trial replacement of two circuits of taxiway lights with 133 direct current (DC) series, simplified LED fixtures and different power supply & control equipment.  The energy savings will exceed US$90,000 over the 20-year life of the fixtures.  Emissions reductions include five million pounds (2,268,000 kilograms) of carbon dioxide and 4,700 US gallons (17,790 litres) of gas will be saved, thanks to fewer maintenance trips to replace incandescent bulbs.
In 2007 the Hawaii International Airport replaced 1,755 30-watt incandescent taxiway lamps with 1W high-intensity LED lamps.  The swap, which also included smaller isolation transformers, is saving the airport 300,000 kilowatt hours (kWh) a year and US$27,000 annually on its power bill.
Energy savings is not the only benefit of switching to LEDs.  Airports have found out that lighting system costs are drastically less with solar LED lighting fixtures.  For example, the Waterkloof Air Force Base in South Africa recently installed several hundred solar-powered LED lights: taxiway edge, runway end and runway threshold lights, plus a solar LED windsock. Manufactured by Victoria-based Carmanah Technologies Corporation, installation took just a few days and none of the trenching and disruption required by traditional wired systems.  Hardware plus installation cost a fraction of that of a wired system.
This April, according to Danver, Massachusetts-based Osram Sylvania, developer of LED technology solutions, one of its original equipment manufacturer (OEM) customers will begin offering LED taxiway guide signs and a retrofit for its halogen product.  “What has been used in this field for a standard sign has been two 48W halogen lights with a 2,500-hour life. We are working with an OEM using a 22W LED replacement with a 50,000 hour-plus life,” explains Leslie Trudeau, display/optic business unit manager, entertainment with the company.
These examples hint at why momentum is gathering in the embracing of LED technology by airport operators.  The bottom line though, is that LED lights last far longer than incandescent or halogen lights: 100,000 hours is a common estimate and some manufacturers believe it could be as high as 200,000 hours.  They require correspondingly less maintenance and reduce airports’ carbon footprints. And when installed in an electrical system designed to take full advantage of the inherent properties of LEDs, as opposed to electrical systems designed for incandescent lighting, power consumption can be reduced by 98%.
Semiconductors, of which LEDs are an example, have been around since the 1950s, according to Trudeau.  Unlike incandescent and halogen bulbs, which produce light and prodigious amounts of waste heat when current passes through tungsten filaments in gas-filled bulbs, Trudeau explains: “Light is generated by an electron field passing over a crystal lattice.”
LED lights are now found in several high-powered airside applications (ADB)

The light-emitting part of an LED light is called the die, and can measure less than four-one hundredths of an inch (one millimetre) on a side.  Add some electronics to the packaged LED and a heat sink and you have what is called a light engine: “Its most basic form is an LED on a circuit board with optics and a connector,” explains Patrick Durand, worldwide technical director with Montreal, Canada-based Future Lighting Solutions.
The first blue LED used a semiconducting material called indium gallium nitride.  White and other colours have followed.
As crystal lattices have become more efficient, manufacturers have been able to build brighter LEDs, making them attractive to the aviation industry.
Although most of us have been brought up to think and talk about the light output of bulbs in terms of watts, power consumption is not a measure of light output. It is the lumen. To illustrate, an incandescent produces eight to ten lm/W.  An LED produces 100 or more lm/W.  Lm/W is a measure of efficiency, Durand notes.
According to Ed Runyon, advanced technology manager with Columbus, Ohio-based ADB Airfield Solutions, airports first used LED lighting on the airside in 2002, for elevated taxiway edge lights, which are the lowest-brightness applications.  That year the Vancouver International Airport ran its first pilot project with LED taxiway edge lights. It was a test project for the airport and manufacturers (the airport tested lights from three manufacturers) alike.  Encouraged by their performance, the airport then replaced approximately 200 incandescent lights with LED elevated edge lights.
The next year, inspired by the looming need for generator and switch gear upgrades that would have cost as much as C$1.5 million, the airport installed 78 flush mounted, eight-inch centerline LED lights on a new taxiway.  The upgrades were deferred.
In a discussion at the time of the potential of LED lighting for airside use, the airport commented: “LEDs are not approved for runway use because they don’t meet the required light intensities, at least not yet.  The light output is far less than that of tungsten-filament lights.”
In the following years, Runyon recounts: “LED manufacturers developed several new generations of brighter LEDs, allowing them to be used in more airfield lighting applications such as obstruction lights and taxiway centreline lights.  In 2002, the idea of using LEDs in the highest brightness applications was just a dream.  With the latest generation of high brightness LEDs, we have been able to develop products that meet photometric requirements for runway guard lights, airfield guidance signs, runway centreline lights and runway touchdown zone lights.”
Solar-powered LED lights are portable and offer independence from power systems. (Avlite)

There are other critical, ongoing challenges besides increasing light output in developing LED lights for aviation applications.  First among them, LEDs, unlike incandescent lights, dislike heat.  Like penguins, they thrive in sub-zero temperatures.  Improving efficiency reduces the amount of heat LEDs emit.  Fortunately, Durand says: “The more efficient an LED becomes, that is, more lm/W it produces, the less heat is developed and the less the thermal management costs.”
Still, heat sinking is a real problem.  Trudeau illustrates the challenges: “Take in-ground lights.  They could be in Phoenix or Afghanistan.  You are heat sinking the light with nowhere for the heat to go.  The LEDs are getting more efficient, with more [light] output and less heat.  Heat is your number one concern.  Heat management, heat management and heat management are the three most important things about LEDs.”
Optics are also a challenge in the development of LED lighting.  Adding more LEDs for higher-brightness applications might seem to be the ticket, and up to a point this is correct; for example, one solar LED light for runway applications manufactured by Avlight, an Australia-based subsidiary of Sealite Pty Ltd. contains 36 ultra-high intensity LEDs.
Durand comments: “If you put enough LEDs together with the right secondary optics, there are not many specifications you cannot meet.  The caveat, however, is that adding more LEDs is more costly and there needs to be enough space to properly cool the LED system.
“The goal is always to increase efficacy, light output and colour quality. The challenges are really from an optical system standpoint.  Making the product work more efficiently for approach lights is a question of how we make optimal use of the light generated by the LED.  Having precision optics design is much more important to LEDs.  An inefficient design may require two to three times as many LEDs.”
LED technology has advanced to the point where they can be used for almost all airside applications, except for approach lights and high-intensity runway edge lights.  ADB, for example, offers L-850A LED runway centerline lights, L-804 LED runway guard lights and LED lights for 14 other airside applications, according to the company’s website.
But that is merely today’s news.  Trudeau notes: “We will have LED approach lighting within one year, according to our customers.”
Chris Proctor, Director, Sealite Pty Ltd, describes how advances in LED technology have permitted corresponding improvements in his company’s solar LED aviation lights.  “As LEDs have become brighter, two things have happened.  Firstly, we can build lights to meet specifications that couldn’t be reached in the past, such as medium intensity obstruction lighting.  Secondly, the power required to drive them at lower levels reduces significantly.
For example, our new EAGLE fixture utilizes latest generation LEDs and driving circuitry to meet FAA L-861 runway photometrics.  Our earlier fixtures could run from battery power alone at this intensity setting for 20 hours.  With advanced LEDs and optics, we can now meet these photometric requirements using half the power of our previous models: the light will now run for over 40 hours at its L-861 settings.”
 
Power struggle
There is another, twisted dimension to this power story: the potential of LEDs have been limited because they have had to make their debut in airside lighting systems designed and powered for incandescent and halogen fixtures.  LEDs only need a system carrying around 2.8 Amperes but the incandescent circuits onto which LED fixtures are being retrofitted are 6.6A.
Manufacturers have had to add circuitry to enable such retrofitting.  The extra electronics gobble electricity, robbing LEDs of much of their inherent efficiency.
The electronics that manufacturers have had to add to make LEDs behave like incandescent and halogen fixtures in terms of colour and light output at different intensity levels is yet another compromise.  But this particular hammering of square LEDs into round Federal Aviation Administration (FAA) certification requirements, so to speak, is beyond the scope of this article.  Suffice to say that the situation is rather like allowing cars to operate in the company of horses only if they too eat hay.
The first LED airside applications were taxiway lights (ADB)

The Atlanta airport trial mentioned above illustrates several advantages of an LED-friendly lighting circuit over a conventional design.  Compare the two: The 5000-volt cabling for conventional lighting circuits carries around 3300V.  The light fixtures on each circuit are supplied electricity and controlled by a 20kW, constant current regulator (CCR) that weighs 1,100 lbs (499 kg) and occupies 26 cu ft (0.74m3) of space.
In that trial, an existing taxiway circuit and its respective CCR were replaced with ADB’s new Advanced Power Supply system (APS).  It consists of one 1kW ADB APS feeding low voltage Pulse Width Modulated (PWM) current to APS LED taxiway edge lights.  This APS weighs about 15lb (6.8kg) and occupies only 1.2 cubic ft (0.03 m3) of space.
The PWM current drastically simplifies the LED fixtures design, they draw less power and emit no EMI due to switching electronics, thereby extending the life of the fixtures.  The APS system uses 98% less energy.  Also, the reduced field voltage for a full load 1KW APS (about 500V) means extended cable service life, increased safety, and substantial energy cost savings.
The Atlanta trial, which was actually a very simple retrofit to do, is a mere taste of what is possible, considering that this airport has 17,000 airside lights.  (ADB reports that Toronto’s Pearson International Airport has 194 CCRs.)
Navaid Lighting Associates, Inc Saltillo, Mississippi and Visual Aid Services, Windsor Connecticut provided design and consulting services on an FAA project that, in 2006, installed an analogous system in the Prescott airport in Arizona.  “We put in a system with a 2.8A circuit, as opposed to the standard 6.6A circuit.  We dim the lights with the actual DC current in the circuit, with no electronics in the fixture.  The system has been in operation for four years with no failures,” explains David Rainey, VP Airfield Systems Development, Navaid.  “Prescott says we have a system that is maintenance free.
“Our circuit, compared to a lighting circuit with 300 incandescent lights, costs 5-7% of the cost of operating the incandescent circuit.  Till now LED lighting for runway and taxiway applications have had to conform to standards for incandescent lights.  We feel that this is the wrong approach.”
Seward Ford, training instructor and associate with Navaid Lighting Associates and owner of Visual Aids Services, adds: “What we find is that the technology leads the development of new standards.  We would like to see an airport team up with a manufacturer and install the Prescott system or something very similar.  Given good results, other airports would pick up on it.  Then the FAA would probably come in and revise the standard to take advantage of the new technology.  Airports will have to be the ones to push the revolution.”