LEDs and Aviation Illumination, Ascending to New Heights

The Aviation industry and airfield signage specifically, utilize LED lighting technology more than most other applications today, both in the military and commercial sectors. “Their attributes are well-known – crisp lighting, energy efficiency, long lifetimes, low voltage requirements, compact size, fast on/off time, shock resistance and no color filter requirements. Applications for LED illumination in aviation range from wing-tip lights to indicator lights on flight decks to pilot guidance lights on airfields to mood lighting in aircraft cabins” (Les, 2009). Here at Norlux, we develop light engines, drivers, and power supplies for both air and ground based aviation applications; and business we do with companies within the aviation realm is certainly thriving. It seems LEDs found a perfect application fit to showcase their many well-known attributes.

Upgrading old or obsolete lighting technologies pose challenges within the aviation industry, and inching towards the future is never as easy as it seems. “Work is progressing to leverage the advantages of LED lighting in the aviation industry and to overcome challenges presented by the technology, such as in the areas of thermal management and in retrofitting the technology into existing lighting systems” (Les, 2009). Raleigh-Durham International Airport offers a great example of the costs in time and money to overhaul their entire runway lighting system in order to take advantage of what LED technology provides. “Officials at Raleigh-Durham International Airport (RDU) in North Carolina realized they were spending a lot of money maintaining an antiquated airfield lighting system. The lighting fixtures were subpar. The cable was old and cracking and meg-ohm readings for many of the circuits were at zero, which meant the airport had to keep pumping up the power to feed the lights. Signage was also a problem. Some were very bright; others rather dim. Some signs were even bright and dim within the same unit” (Nordstro, 2010). "The FAA wasn't very happy with us," recalls Steve Pittman, deputy airport director of Facilities, Engineering and Maintenance. "They didn't demand that we upgrade our lighting system, but they did suggest we do something about our signage lighting" (Nordstro, 2010). “RDU took the hint and initiated a $20 million project to convert its incandescent airfield lighting system to LED technology. Over the last two+ years, roughly 230 signs and 3,200 bulbs were changed - everything from taxiway edge and centerline lighting to runway centerline lights, obstruction lights, touchdown zone lights, runway end identifier lights, and elevated and in-pavement guard lights” (Nordstro, 2010). The makeover, as it turns out, was nothing short of spectacular. “Everything that can be LED is LED. It's an amazing look at night" (Nordstro, 2010).

So why make the change to LED lights? Costs in terms of man-hours as well as dollars are a driving force. “A primary benefit of LED lights is the lack of maintenance required once they are installed” (Airport Technology.com, 2008). “LEDs are a very efficient light source [for aircraft] and can significantly reduce seat-mile costs and schedule upsets because of their dramatically increased reliability over filament lights” (Les, 2009). Cost savings and energy efficiency always lead the list of attributes associated with LEDs. “With the former incandescent lighting system, RDU maintenance crews were replacing bulbs twice a year per fixture. Operations crews were constantly checking the airfield for burned out lights. There were operational consequences as well. Airfield pavement sections had to be closed when bulbs were replaced. Electrical circuits were tied together in haphazard and confusing ways, which made maintenance time-consuming and costly” (Nordstro, 2010). “Replacing every bulb in every light at least twice a year was not only a safety issue, it was quite costly in parts and labor. Subsequent analysis showed that moving from incandescent lighting to LEDs would save approximately $400,000 per year in energy and maintenance costs including labor and parts” (Nordstro, 2010).

Energy efficiency and the “green” aspects of LEDs are always attractive elements to any application, and aviation lighting is no different. “LEDs are the hot item in lighting these days, both due to their energy saving properties and also the expected long life of the light source” (Airport Technology.com, 2008). Solar-powered LEDs are also a viable option, especially for some smaller airfields. As a versatile lighting alternative for “temporary runways, remote airfields without grid access, or as an emergency-response application, solar-powered LED lights offer distinct advantages. Self-contained, portable and wireless solar LED lights can be installed and operational in a matter of hours to provide bright and reliable lighting” (Airport Technology.com, 2008). "With a quick set-up, no scheduled maintenance and complete freedom from the costs and logistical restrictions associated with installing and operating a grid or generator-powered system, solar LED lights offer a versatile and cost-effective alternative for a variety of applications” (Airport Technology.com, 2008).

With the ten- to twelve-year lifespan of LEDs (on average), users employing LED lighting technologies can reallocate manpower and funds away from expensive and time-consuming maintenance duties onto more customer-centric tasks. It goes without saying that in the transportation/aviation industry “organizations that are responsible for large assets, the move to green technology is important” to keep business competitive, solvent and on the cutting edge of technology (Airport Technology.com, 2008).

Sources:
http://www.photonics.com/Article.aspx?AID=37892 
Caren B. Les, Photonics.com – June 2009

http://airportimprovement.com/content/story.php?article=00203http://airportimprovement.com/content/story.php?article=00203
Robert Nordstro, Airport Improvement Magazine - September 2010

http://www.airport-technology.com/features/feature46764/
Author Unknown, Airport Technology.com – December 2008

LED Thermal Management

It can be a huge challenge to keep electronic products running cool, and LED lighting products are no exception.  An LED’s light output is determined by the amount of current applied to the LED and the subsequent management of the heat emitting from the LED.  The higher the electrical current, the more heat generated at the LED junction.  This heat can lead to output deterioration, which limits the amount of light that can be generated by an LED, reducing the life of the LED over time.

Designers need to account for temperature factors in the early stages of the design process to mitigate heat’s potential adverse effects.  Thankfully, the effects of heat in an LED system can be understood through calculation and simulation.  A model that is used frequently is the thermal circuit model.  These thermal circuit models are similar to resistor circuits using Ohm’s law.  An LED’s power dissipation is modeled as a current source, thermal resistances are modeled as resistors, and the ambient temperature is modeled as a voltage source.  The thermal resistance must be minimized to increase an LED’s light output or its useful ambient temperature range for a given power dissipation.

Minimizing the thermal resistance can be done in a number of ways.  Conduction, convection, and radiation are the three means of heat transfer.  Conduction and convection are typically used to transfer heat from LEDs to ambient temperature.  Convection requires the movement of air, which in many instances requires a mechanical means of moving air, such as a fan.  In many cases, fans are not an acceptable way of cooling LEDs in light fixtures due to noise and reliability concerns.  Conduction, however, is the transfer of heat from one solid to another, and is typically the way LED systems are cooled.  Conduction requires the accurate design of heat sinks to properly cool an LED system in its intended environment.  This is where the thermal circuit model is valuable.  The thermal resistance value of a heat sink can be calculated for the specific LED system and its temperature environment.  This information allows for the proper selection criteria for a standard heat sink or provides the information needed to design an effective thermal management system.

Designers at Norlux are experienced in LED thermal management and the design of thermal systems.  If you are facing challenges regarding LED performance and LED heat dissipation, contact Norlux for a solution that’s ahead of the curve.