Link to Document

Conventional grid- or generator-dependent airfield lighting systems are less than ideal for rapid deployment to areas without reliable power sources. Ideally, the solution should be lightweight, exceedingly tolerant of combat theatre conditions, provide hands-off, maintenance-free operation and be capable, literally, of being set up in multiple ways (Table 1) by a handful of people, a mallet, a shovel and a wheelbarrow. Carmanah Technologies Corp. has advanced the technology of its portable solar-powered light emitting diode (LED) lights to meet these requirements. The company has some 65,000 units for airfield applications in the field, including more than 30,000 units owned by the U.S. Department of Defense for forward operating base applications.

Uses include permanent, semi-permanent and emergency lighting for runways and runway thresholds, intersections, taxiways, obstructions and barricades, helipads (Figure 1), aprons and airfield signage; a visual approach path indicator is also under development. There is a growing portfolio of complete and permanent airfield lighting installations, as shown in Table 2, at commercial and general aviation (GA) airports, at lower capital and operating costs than traditional wired-in systems. Each unit operates independently of any external power source, and can be set to turn on automatically at dusk and off at dawn. With certain models, operators and pilots can change settings or remotely activate them. Military users in locations worldwide include the U.S. Air Force, Army and Marine Corps, Air National Guard, and North Atlantic Treaty Organization Forces, as well as national defense forces from other countries.

Carmanah currently utilizes LEDs in white, amber, red, green and blue. LEDs are extremely durable and have a 100,000-hour operating life — 20 times that of incandescent bulbs and twice as long as fluorescent lamps. LEDs also produce little heat, a property that makes them night-vision goggle or NVG-compatible. According to feedback from the USAF, U.S. Army and Marine Corps pilots, they provide crisp, precise light output with no blooming or blinding effect for incoming air traffic.

LED-based vs. conventional airfield lighting

Since about 2003, LED lights have begun replacing conventional lights in traditional airfield lighting systems. The following are two real-world examples:

After evaluating LED taxiway lights, one international airport installed them permanently on two controlled taxiways. The airport replaced approximately 200 incandescent lights with LED elevated edge lights on one taxiway, and installed about 78 flush-mounted, eight-inch centerline LED lights on another taxiway. Their reduced overall power consumption of approximately 30% to 40% of that for incandescent lights allowed the airport authority to defer generator and switch gear upgrades.

Another international airport installed 101 LED elevated edge lights on one taxiway. The following year, it installed 290 LED lights for the centerlines of four high-speed turnoffs for a runway, and then LED centerline lights for two additional taxiways. It was calculated that an 11 W LED consumed $1.77 worth of electricity per year, vs. $4.14 for a 30 W incandescent bulb. A cost/benefit analysis assumed that incandescent bulbs would be replaced twice per year, although three times a year is not uncommon. LED bulbs, on the other hand, are expected to last at least 10 years. Associated with this advantage are fewer airfield maintenance visits, with their associated cost and risk.

Portable solar LED airfield lighting

Unlike some emerging alternate energy technologies, whose effectiveness hinges on the development of exotic energy-storage media, the properties of LEDs lend themselves to portable solar-powered applications based on mature commercial technologies. This is illustrated by Carmanah's model A601 taxiway/obstruction light, which measures 5.5 inches in diameter and 7 inches high (13.97 cm × 17.8 cm) and weighs 4.85 lb (2.2 kg). A 4.5 in. × 4.5 in. (11.43 cm × 11.43 cm) solar panel array delivers 1.4 W to an LED cluster, which has a daylight visual range of up to two miles (3.2 km), as shown in Figure 2. The A601 and model A704-5 conform to the International Civil Aviation Organization Annex 14 for low-intensity obstruction lights, taxiway and runway edge lights for visual flight rule operations.

The solar panels also charge two, 2 V pure-lead thin plate with starved-electrolyte batteries, which power the LEDs at night. In a flashing configuration, the minimum operating autonomy is 300 hours and 150 hours for steady illumination. An infrared programmer can be used to change flash codes, check battery levels, adjust intensities, and activate and deactivate the A601s for storage. As LEDs produce virtually no heat, the units require no venting, except that the polymer-encapsulated design has only a small one-way battery vent. Carmanah rates the A601 for operation within a latitude range of 55° S to 55° N, and a temperature range of -40 °F to 176 °F (-40 °C to +80 °C). However, its operational limit has been pushed as far north as the 62nd parallel at Canada's Yellowknife Airport, NWT and Elmendorf AFB, AK. The A601 requires a minimum solar exposure of 1.5 to 3 peak sun hours to maintain maximum autonomy. It is waterproof as per IP67 (NEMA 6); resistant to salt-fog corrosion and vibration as per TP1861E; explosion-resistant as per MIL-STD-810E method 511.3; and CE-approved as per EN 60945:1997. The A601 is designed for about five years of continuous operation, after which it can be recycled.

Temporary and permanent installation

Early uses for the A601 were in emergency and temporary applications. Permanent installations eventually followed. One airport has used 60 A601s since February 2003 for a rolling security barricade. Until it installed the solar lights, it reportedly spent $900 every three months for deep-cycle batteries. Airports are also using the A601s as temporary replacement for damaged fixtures, including cases when plows sometimes break off lights (as many as 100 broken in a single storm have been reported) and damage underground cabling during snow removal operations. Maintenance workers traditionally have to use jackhammers to dig up the ground before carrying out repairs. Such work requires two operators, two electricians and a half-day on the airfield, at a minimum cost of about $425, considerably more than the cost of one A601. Even when installed at extreme northern latitudes as early as November, these can operate unattended until warm weather permits repairs to wired equipment.

A group of solar- powered runway, threshold, taxiway and obstruction lights can also be installed adjacent to their wired-fixture counterparts to create a complete emergency lighting system (Figure 3). As long as the regular lights remain illuminated, the solar-powered lights stay turned off. If the regular lights fail, the darkness triggers the parallel system to come on automatically. Within 10 seconds the taxiway and runway are again ready for use. In one implementation of such a configuration an airport in the Caribbean region installed a parallel system of 240 portable runway and taxiway edge lighting units; an aviation performance report noted they were visible from 15 NM out at an altitude of 15,000 feet on a clear night.

The solar lights can also be used to replace or complement passive systems, such as the retro-reflective taxiway markers for nighttime visual guidance at GA airports. For example, A601s can be mounted on existing retro-reflective markers (Figure 4), using a small base plate and three bolts for each light. This was carried out at one large GA airport in California in 2004, with up-front capital savings of $850,000 over a traditional system and $16,000 per annum in energy savings.

Installation guidelines

The installation process is essentially reduced to correctly siting the units, which can be done with transit and measuring tape following the guidelines for conventional wired lighting fixtures (or by naked eye estimation in emergencies). The units are installed with a vertical orientation, and no special adjustments are required to ensure adequate exposure to solar radiation. An exception is the elevated runway guard lights shown in Figure 5 along with their separate solar power panel array, which should be oriented toward due south, and at an angle approximately equal to the location's latitude.) For the A601, for example, the location would need a total solar exposure that provides the equivalent of at least 1.5 peak sun hours to maintain maximum autonomy. The A704-5 runway edge units contain power-point tracking circuitry that maximizes the amount of energy that can be obtained for the solar cells for given lighting conditions. With freestanding placement (Figure 6), two workers can setup a complete emergency lighting system for a 5000-foot runway in 20 minutes.

The relative installed cost of conventional and solar-powered LED systems varies from site to site, but a well-documented case in California suggests that a cost ratio of 10:1 might be a fair rule of thumb. Furthermore, even a small airport can realize continued savings on the order of $10,000 per year by eliminating expenditures for run-way and taxiway lighting electricity. Another factor to consider is that complete installation at an existing airport requires no disruptions to aircraft operations. In addition to the greatly simplified installation process, the logistical burden for a solar-powered lighting system, a major concern for forward operating bases during military operations, is essentially reduced to zero.

Harsh environments

Carmanah's solar-powered airport lights are self-contained, maintenance-free, rugged and weatherproof. A concern with any solar energy system is the potential for interference caused by precipitation, especially snowfall. However, despite receiving 350 inches of snow annually, one airport reports that the morning sun quickly melts what little snow accumulates on the solar panels. In addition, other units, such as the A702 and A704-5, feature vertically oriented solar panels. They resist the accumulation of precipitation while at the same time gathering scattered light in overcast conditions.

Shock-proof and vibration-proof, the units are suited for the rough handling to be expected in a mobile environment, where air bases can be required to frequently relocate. They can withstand low-energy collisions with taxing aircraft, and can be mounted on breakaway (frangible) couplings to minimize damage to the aircraft and the unit (Figure 7).

Table 1. Portable solar-powered LED lights installation options.

Installation Options
Freestanding.
Bolted to plywood base and set on leveled ground.
Mounted on supplied stake driven into unprepared ground.
Mounted on supplied stake, set in concrete-filled hole.
Mounted on existing retro-reflective post.
Cabled together (A704-5 units) and powered by generator to provide maximum-intensity illumination in extremely low-sunshine Afghanistan environment.

Controlling the lights

Air traffic controllers exercise complete control over airfield lighting using airfield lighting control and monitoring systems. They raise and lower runway lighting levels and activate and shut down blocks of lights according to weather conditions and aircraft operations. Responding to their need for control, Carmanah developed the A704-5, which is a highly controllable solar-powered LED airfield lighting solution.

Already in use for defense and civilian applications, users can switch A704-5s on and off using a wireless controller, which has a range of up to 2.5 miles (4 km). Up to eight groups of lights can be created, with each group controlled independently for multiple runway/taxiway applications. The controller can also be used to select among six autonomous or high-brightness temporary lighting levels; the A704-5 has been reported to have a visible range from up to 15 NM away in clear nighttime conditions. An optional defence application allows switching between visible and infrared light output. Pilots can also activate the lights for 15-minute intervals using a 256-bit encrypted 900 MHz RF signal. These and other features can be viewed at http://www.carmanah.com/quicklinks/a704-5_video.html.

Table 2. Examples of airports using Carmanah portable solar-powered LED lights.

Location	Number of lighting units	Purpose
Elmendorf AFB, AK	250+	Taxiways, aprons, barricades (permanent)
Bagram Air Base, Afghanistan	1222	Taxiways, runways, threshold, obstruction, heliport (permanent)
Chicago O'Hare International Airport	60	Barricade lights
Lynden Pindling International Airport	240	Parallel taxiway/runway emergency backup system (permanent)
18 Family Island airports, Bahamas	1441	Taxiways and runways (permanent)
Truckee Tahoe Airport	500	Taxiways (permanent)

ABOUT THE AUTHOR

Allister Wilmott is the manager of the Aviation Lighting Division with Carmanah Technologies Corporation. After graduating from the University of Victoria in 2001 with a bachelor's of arts in geography and playing a season of professional basketball in Finland, he joined Carmanah in 2002. That year, he launched the company's aviation division and acted on its vision to introduce solar LED lighting to the international aviation industry. He is a member of the Illuminating Engineering Lighting Society of North America Aviation Lighting Committee (IESALC) General Aviation Committee and is managing the test program with the Federal Aviation Administration for solar LED taxiway and elevated runway guard lighting.