Issues With Use of Airfield LED Light Fixtures (2012)

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5 Current PraCtiCes Airfield lighting systems encompass a large variety of types varying in luminous intensity, color, and geometric con- figuration. These systems demarcate runways and taxiways, provide traffic control for movement of aircraft and other vehicles on the airfield, indicate the location of hazards and obstructions, and provide information about ambient con- ditions on the airfield. Figure 2 shows a simple schematic of a typical LED airfield lighting fixture. A series of FAA Advisory Circular (AC) and Engineering Brief (EB) docu- ments describe the design, performance, and maintenance requirements of airfield lighting systems. The FAA also has a process for the certification of airfield lighting fixtures that meet the performance requirements, and publishes a list of certified fixtures. Key FAA documents pertaining to airfield lighting and uniform resource locators (URLs) for obtaining these documents online are listed in Appendix D. As described in the previous chapter, LED output contains little to no infrared energy, which means that LEDs do not radiate heat directly. Because of this, it has been stated that air- field fixtures using LEDs might not generate sufficient heat to melt snow and ice that could build up on fixtures, making them less visible (Marsh et al. 2008; Rosenkrans 2008), although LED taxiway lights installed at Pullman–Moscow Regional Airport in Washington State did produce enough heat to keep snow and ice melted (Moll 2006) and no problems regarding snow and ice buildup were reported from Canadian airports (Seymour 2007). At any rate it does not appear that this is an inherent issue with LED systems, because substantial heat can be generated in the LED junction, which must be conducted away from the chip for efficient operation of the light source (Bullough 2003). Redesigned LED taxiway lights that conduct heat from the chip through a heat sink that makes contact with the fixture lens (Gu et al. 2007; Taylor 2010) were found to be able to prevent snow and ice buildup at very low temperatures. At present, not all LED light fixtures produce the temperature increase on the fixture lens specified by the FAA in its EB for keeping the lens clear of snow and ice. The use of heaters with LED light fixtures has been reported by several airports, as described in chapter four, Operation and Maintenance Issues. types of LeD airfield Fixtures in use As described in the previous chapter and in Appendix A, LEDs have a number of characteristics that appear to be well- suited for aviation signaling applications. Figure 3 illustrates the types of lighting systems in use among the participants in the survey on LED use. The most common types of LED lighting systems among survey participants are elevated taxiway edge lights, in- pavement taxiway edge lights, illuminated wind cones, and obstruction lights. In general, Figure 3 shows that LED taxi- way lighting systems tend to be used more often than LED runway lighting systems. Indeed, LED taxiway lighting systems have been available longer than LED runway light- ing systems. One reason for this is that per FAA’s AC 150/ 5345-46, “Specification for Runway and Taxiway Light Fix- tures,” taxiway lighting systems tend to have lower luminous intensity (candlepower) requirements than runway systems, which must be seen from greater distances than many taxi- ways. LED lighting and signage systems for traffic control (elevated and in-pavement runway guard lights and L-858 signs) also have relatively high incidence of use compared with other types such as runway lights and touchdown zone lights (Figures 4 through 10 show examples of LED airfield lighting fixtures). Many of the survey respondents reported that their air- ports have had LED airfield lighting systems installed for more than 12 months (Figure 11). Most of the time airports acquired LED systems from a single manufacturer (reported by 15 survey respondents), and less frequently by more than one manufacturer (reported by 5 respondents). LeD airFieLD Lighting ChaLLenges Compatibility of LED airfield lighting systems appears to be among the primary concerns and challenges regard- ing this relatively new technology. Many of the installa- tions that have been described in the literature and in the survey of organizations regarding LED airfield lighting (Appendix B) were replacements of fixtures on the exist- ing electrical infrastructure (Figure 12). It has been pointed out that just as with roadway traffic signals (Urbanik 2008), the electrical infrastructure for most airfield lighting (see Figure 13) was designed for use with incandescent lighting systems, requiring substantially higher power. Redesigned systems with LED electrical characteristics in mind (Tay- lor 2010), such as lower voltage parallel circuits (Vaughan chapter two Current PraCtiCes anD ChaLLenges in airFieLD Lighting

6 FIGURE 2 Simple schematic diagram of an LED airfield lighting fixture. FIGURE 3 Percentage of survey respondents whose airports have LED versions of various lighting system types in use. FIGURE 4 LED elevated taxiway edge light. FIGURE 5 LED in-pavement taxiway edge light. FIGURE 6 LED illuminated wind cone.

7 2011), could result in more efficient LED operation (Nadel 2009) and even greater electrical energy savings than has been reported in some LED conversion projects. The FAA (Seymour 2007) and some airports such as Orlando International Airport (Barczak et al. 2010) and Rafael Núñez International Airport (Colombia) (Marsh et al. 2008) have investigated new electrical infrastructures to overcome reduced efficiencies of LEDs operated on legacy electrical circuits. Maximizing the re-use of existing facili- ties and the electrical staff’s experience with these systems is important so that staff can apply their expertise to new infrastructures, minimizing the need for re-training. Indeed, LEDs may offer potential for eliminating some of the electrical infrastructure traditionally associated with air- field lighting (Rosenkrans 2008), and in some cases they are already doing so. An FAA EB on this topic (No. 76) entitled “Using Solar Power for Airport Obstruction Lighting,” has been published (see Appendix D). Randolph County Airport Indiana has installed several solar-powered LED obstruction lights (Cook 2011). Because LED technologies are evolving at a rapid pace, the characteristics of electrical systems optimized for their FIGURE 7 LED obstruction light. FIGURE 8 LED elevated runway guard light. FIGURE 9 LED in-pavement runway guard light. FIGURE 10 LED runway end identifier light.

8 performance are also likely to evolve. Tensions within air- ports to take advantage of near-term savings in energy and maintenance cost with simpler replacement project scopes, versus longer-term and larger savings with more complex electrical and lighting system alterations having larger initial costs, will likely exist for some time to come. Electrical infrastructure issues are certainly not the only challenges related to LED airfield lighting systems. As described earlier, the lack of heat emitted directly by LEDs has been a concern. LED airfield lighting fixtures also generally have higher initial costs than their incandes- cent counterparts (Marsh et al. 2008; Muriuki 2008; Hough and Gilbreath 2010), and this was confirmed in the sur- vey conducted for the present ACRP study (Appendix B). Moreover, some airports are structured so that any reduced operating or maintenance costs are not realized by the same department that procures these more initially expensive FIGURE 11 Length of time survey respondents have had LED airfield lighting systems installed. 18 16 14 12 10 8 6 4 2 0 less than 6 months 6-12 months Duration LEDs have been installed N um be r of r es po nd en ts 12+ months FIGURE 12 Distribution of LED installation types on new facilities, as LED-fixture- only replacements on existing facilities, or as fixture replacements alongside replacement of part or all of the electrical system (e.g., controls or regulators) on existing facilities (percentages exceed 100% because some respondents provided answers for more than one LED airfield lighting system at their organizations). Type of installation N um be r o f r es po nd en ts New facility 12 10 8 6 4 2 0 Existing facility (fixtures only) Existing facility (fixtures, electrical components)

9 fixtures, presenting a possible barrier to their specification (Vaughan 2011). Another challenge regarding LED airfield lighting is where information about LED systems can be obtained, and indeed one of the objectives of the present ACRP synthesis study is to gather this information in a single document. Figure 14 shows the primary sources of information about LEDs used by the survey respondents. The most frequent source of information (cited by 20 survey respondents) is vendors or manufactur- ers of LED systems; each of the other sources—colleagues, technical reports, and trade publications—was cited by fewer participants in the survey. FIGURE 13 Simplified schematic diagram of an electrical circuit for an LED airfield lighting system. FIGURE 14 Sources of information about LEDs according to survey respondents. OrganizatiOn OF tOPiCaL ChaPters The subsequent chapters of this report summarize the issues with LED airfield lighting with respect to installation, oper- ation and maintenance, and the economics of these systems. They are intended to provide a snapshot as of late 2011 of the status of LED airfield lighting, the potential advan- tages of using these systems, and the challenges that face decisions to use LED technologies. Chapters are organized largely around the structure of the survey questionnaire presented in Appendix B, with a summary of relevant lit- erature to supplement the responses from the participating survey respondents.