LED Airfield Lighting System Operation and Maintenance (2015)

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42 C H A P T E R 4 Circuit Configuration LED lighting systems consume less energy and have a longer life than other lighting sources. Because of their low energy consumption, there has been a tendency to increase the number of fixtures on a given circuit to optimize the capacity of the constant current regulator (CCR). Many airports have implemented LED lighting through grant-funded or capital projects where the installation is performed by electrical contractors. However, some airports replace existing fixtures with LED lights using their own maintenance staff. This chapter presents best practices for circuiting LED fixtures, with a focus on maximizing CCR capacity and optimizing mainte- nance practices. LED fixtures typically require 50% to 75% less power than incandescent fixtures as shown in Figure 31. This decrease in power consumption is a tremendous savings when extrapolated across an entire airfield. To maximize the benefits of this new technology, several factors must be considered. Circuit Load Calculation In reviewing what effect more efficient fixtures will have on AGL systems, the research team determined several strategies an airport can implement. LED AGL loads can realize a significant reduction in energy consumption, as illustrated below. The load calculation for any given circuit is as follows: 2TL F FL XL L CR A( )( ) ( )= × + + × × where TL = Total Circuit Load (VA) F = Quantity of light fixtures FL = Load of Each Light Fixture (VA) XL = Load of Each Isolation Transformer (VA) L = Cable Length (Ft) CR = Cable Resistance (Ω/Ft) A = Circuit Ampacity (High Step) The calculation below shows that the circuit load for a taxiway centerline circuit using 100 bidirectional incandescent L-852C type fixtures and 20,000 feet of L-824 cable will be 5,980 VA. This calculation illustrates a circuit current of 6.6 Amps and the cable resistance is Operation Considerations

Operation Considerations 43 derived from the NEC Chapter 9 Table 9 value for #8 AWG cable (0.78 ÷ 1,000). The calcula- tions are defined as follows: 100 45 8 20,000 .00078 43.56 5300 680 5980 TL TL TL ( )( ) ( )= × + + × × = + = A load this size would typically be placed on either a 7.5 kW or a 10 kW CCR. For this example, a 7.5 kW CCR has been selected because the load is roughly 80% of the capacity of the CCR. Having established the base model of a typical taxiway centerline circuit, the next step is to inves- tigate the effect of converting to LED fixtures. Circuit Optimization There are several circuit configuration and optimization strategies for direct replacement with LED lighting. These strategies address different goals for the airport and include • Direct replacement with LED lights without any circuit modifications. (Low cost, Low-power factor, Medium flexibility) • Direct replacement with a new properly sized CCR. (High cost, High-power factor, Medium flexibility) • Direct replacement and combining circuits to maximize the load on the CCR. (Low cost, High-power factor, Low flexibility) • 40%–50% loading of circuits to facilitate emergency repairs. (High cost, Low-power factor, High flexibility) The strategy chosen depends on the available budget, energy efficiency, operational strategies, and maintenance strategies. Figure 32 addresses strategies implemented by the airports surveyed. Figure 31. Load comparison of L-861T medium-intensity elevated edge lights.

44 LED Airfield Lighting System Operation and Maintenance Approach 1: Direct Replacement Without Circuit Modifications If the fixtures on this circuit were then converted to LED, the calculation would be as follows: 100 17 3 20,000 0.00078 43.56 2000 680 2680 TL TL TL ( )( ) ( )= × + + × × = + = This would net a circuit load of 2,680 volt-amps. One option would be to leave the exist- ing 7.5 kW CCR in place to service this load. The load of 2,680 volt-amps would be less than half of the consumption of the original circuit. This would result in the least effect to cost and maintenance (Figure 33), although there would be an operational concern. If this CCR were a silicon-controlled rectifier (SCR) type, the taps would have to be adjusted to the new value or else the input current draw would be nearly identical to the original incandescent load [Runyon 2013]. Whether an SCR or Ferro-resonant type CCR, the power factor would be worse when a CCR would be lightly loaded as the voltage would become more out of phase with the current. CCR manufacturers recommend a minimum loading of 60% for CCRs to minimize any power factor losses due to inefficiency. Approach 2: Direct Replacement With a Properly Sized CCR The next option would be to replace the existing 7.5 kW CCR with a 4 kW CCR. This new CCR would be matched to the new load with a capacity at 67% full. Although this method would have higher initial costs, the energy consumption would be at its lowest, and the CCR would still only When installing LED light fixtures to replace incandescent light fixtures on an exis ng series ligh ng circuit, did you: Figure 32. Survey results for replacement of CCR when LED fixtures replaced incandescent.

Operation Considerations 45 serve one circuit. This method would maintain the existing circuit segmentation plan which could be operationally important; however, it would have a higher cost and would not alleviate any existing space constraints within the airfield lighting vault. Approach 3: Direct Replacement and Combining of Circuits on the Existing CCR In the example above, where the 7.5 kW CCR would be only loaded at 36%, it would provide the opportunity to combine several circuits into one circuit. Because roughly 4,800 VA of capacity would remain on this CCR, the facility might choose to add another identical circuit to this CCR. Now, this CCR would be responsible for 200 fixtures and 40,000 feet of cable over two taxiways. This new circuit would have an improved power factor, and perhaps there would be a cost savings by not requiring an additional CCR. Combining these circuits would eliminate the need for an additional regulator, but would increase the affected area if this circuit should fail. This could affect operations and increase the time and effort to troubleshoot the circuits. It might also affect opera- tional flexibility if the tower preferred to illuminate only those taxiways or runways in use. Approach 4: 40%–50% Loading of Circuits to Facilitate Emergency Repairs One of the airports interviewed for the case study indicated the maintenance department preferred to load the CCRs just under 50% to facilitate emergency repairs. By having significant spare capacity in each circuit, maintenance can temporarily jumper an adjacent circuit to it if Understanding CCR Input Currents Figure 33. Effect of CCR inefficiency.

46 LED Airfield Lighting System Operation and Maintenance there are cable failures in that circuit. This approach allows them to get the lights back on quickly and perform cable repairs or replacement at a more appropriate time. This strategy is similar to Approach 1 in that it is the lowest cost when replacing LED fixtures; however, the load on the CCRs must be adequate and the CCRs must be adjusted so they perform correctly. This method does not optimize efficiency of the CCR and will result in a lower circuit power factor. Mixed Circuits with Lights and Signs Another possible scenario on an airfield is the mixing of lights and signs on the same circuit. This is not a preferred configuration and should always be designed according to manufacturer’s recommendations. The issue with placing signs on light circuits is that signs will draw the same wattage on all steps where a light fixture load varies with the step intensity. Lights will require less wattage as the steps decrease, and in turn less voltage, although the current remains constant. Because signs are required by the FAA to have a constant light output across all steps, an airfield circuit that contains both signs and lights and has a high proportion of signs, may experience CCR failure at the low steps. Therefore, the regulator must be designed to avoid a trip in the circuit due to overloading of the regulator. There are also sizable losses in the cable runs because signs are usually spaced farther apart. Placing signs and lights on separate circuits allows for better sizing of regulators. This is the preferred best practice for designing an airfield lighting system. Mixed Circuits with Incandescent and LED Fixtures The most economical method to introduce LED fixtures to an airfield would be to replace old and damaged incandescent fixtures with their respective LED counterparts. Eventually, as all incandescent fixtures fail, the airfield will be completely replaced with LED fixtures. However, this is the exact scenario the FAA is trying to avoid. Per FAA AC 150/5340-30G: The increasing use of airport LED light fixtures on the air operations area (AOA) has caused concerns when LED light fixtures are interspersed with their incandescent counterparts. LED light fixtures are essentially monochromatic (aviation white excepted) and may present a difference in perceived color and/ or brightness than an equivalent incandescent fixture. These differences can potentially distort the visual presentation to a pilot. Therefore, LED light fixtures must not be interspersed with incandescent lights of the same type. Example: An airport adds an extension to a runway. On the existing runway, the runway centerline light fixtures are incandescent. The airport decides to install LED runway centerline fixtures on the new section of runway and retains the incandescent fixtures on the existing section. This interspersion of dissimilar technology is not approved for installation. In addition, defective incandescent fixtures must not be replaced with their LED counterparts. When replacing a defective light fixture, make certain that the replacement uses the same light source technology to maintain a uniform appearance. This guidance indicates that incandescent lighting can be replaced with LED lighting only when replacing an entire system or when there is significant visual demarcation between the old lighting and the new. LED fixtures can be combined with incandescent fixtures on the same lighting circuit with no issue; however, the information on LED circuit inrush gives guidance as to how high to load a CCR. 3-Step vs. 5-Step CCRs for LED Circuits Now that several years’ worth of data from LED AGL systems in use is available, user feedback has inspired changes to the FAA ACs on the use of these systems. AC 150/5340-30H, in Chapter 4, has determined that high-intensity LED lighting systems will be served by 5-step CCRs. The reasoning is that a 3-step CCR cannot adequately reduce the light intensity of these systems at the lowest step. A 3-step CCR has a low step current of 4.8 amps while a 5-step CCR has a low step current of 2.8 amps, nearly half of the 3-step equivalent. Although the AC does not specify

Operation Considerations 47 what constitutes a “high-intensity” LED system, there appears to be a shift in the industry to move LED AGL circuits to 5-step CCRs. LED Circuit Inrush The FAA conducted a study to determine the effects of LED lighting on the operation of a CCR. In the study, the FAA tested five LED taxiway edge lights from different manufacturers. Each light presented a high initial peak power (VA) value then dropped off to a steady operating power (VA) value; however, not all high peak values and steady operating values were the same among the fixtures. The study recommended that light manufacturers limit the peak power and power drop values to 10% of the fixtures operating power value to ensure the CCR could adjust to the overvoltage and overcurrent condition during startup to the steady-state operation phase. Although LED taxiway guidance signs were not included as part of the test, the understanding is they, too, would have a high initial peak power value and then drop off to steady-state operation. Refer to FAA Technical Note DOT/FAA/AR-TN08/29, Light Emitting Diode Taxiway Lighting Effects on Constant Current Regulator Stability for more information. The survey data from one case study indicated an ongoing issue with a CCR “tripping-out” on an LED light fixture circuit. In such cases, several factors can be reviewed to help mitigate the situation for both existing and future lighting circuits. If an existing CCR is tripping-out, the circuit size and load should be reviewed and verified. If the circuit load is within 10% of the CCR nameplate load, remove light fixtures from the circuit until the load is 10% to 15% less than the nameplate load. Operate the circuit with the reduced load. Depending on the manufacturer of the light fixture and CCR, additional light fixtures may have to be removed. If this does not resolve the issue, further investigative testing is required to determine initial and steady-state circuit loads and overvoltage and overcurrent parameters of the CCR. This data can be used to determine if it is a circuit issue or a CCR issue. For new designs, three factors can be implemented to help reduce the potential of overload on the CCR powering an LED light fixture circuit: (1) limit the calculated circuit load, which includes light fixtures, signs, cable, transformer losses, digital control devices losses, etc., to be 85% to 90% of the selected CCR nameplate load; (2) review the LED light fixture peak power and drop-off power value and compare to the fixture’s operating power value, a value difference close to 10% may give you a better performing system; and (3) review the adjustment capabilities and specifications of the CCR for compatibility with high initial peak power circuits. Key Takeaways • Consider the needs of your airfield when evaluating circuit optimization. • For existing circuits, verify existing circuit load and compare to CCR nameplate. • For new circuits, the research team recommends selecting a CCR nameplate load 10% to 15% higher than the calculated circuit load. • Review the specified operating performance of LED light fix- tures, LED taxiway guidance signs, and CCR with manufacturers for proper selection of circuit components.

48 LED Airfield Lighting System Operation and Maintenance Heaters in Elevated and In-pavement Fixtures The need to provide heaters for elevated and in-pavement light fixtures in areas prone to snow, sleet, and ice has been an issue since the start of development and implementation of LED light fixtures. Ice and snow can accumulate and adhere to elevated and in-pavement light fixtures obscuring the light output. Heat, an inherent characteristic of incandescent fixtures was the source of ice and snow melting. LED fixtures produce heat at the light engine; however, this heat is transferred to a heat sink farther from the fixture surface to prolong the life of the diode. Therefore, to replicate the snow-melting capabilities of incandescent fixtures, a separate heating element was designed for both elevated and in-pavement light fixtures to mimic the lamp heat- ing effect of an incandescent light fixture. More than half (65%) of airports surveyed do not use heaters for their light fixtures. How- ever, the survey was not clear on the type of precipitation experienced by these airports. To review more closely, the research team turned to the case studies which included several large hub airports in regions prone to significant amounts of frozen precipitation; with the use and non-use of heaters roughly split in half. Two of these airports, which are geographically close to each other, were split on the debate of whether to use heaters or not. The need for use of heaters is thus inconclusive. The heating activation of incandescent light fixtures is a function of energizing the series light- ing circuit. Case studies indicate that most airports do not regulate the intensity of the lighting cir- cuit to melt snow or that they are energized to the highest intensity in anticipation of heavy snow. These light fixtures are operated based on visibility and runway visual range (RVR) in accordance with FAA Order JO 7110.65, Air Traffic Control, Section 4, Airport Lighting. However, visibility during snow events typically calls for the lights to be on the highest intensity setting. Because the operation and intensity of the incandescent light is based on visibility, rather than ambient temperature, when evaluating the efficacy of LED light fixtures with heaters versus the heat generated by an incandescent light fixture, the heat at each intensity needs to be taken into account (Figure 34). Heaters supplied with LED light fixtures are thermostatically controlled and are activated when the circuit is energized. According to manufacturer information, the thermostat typi- cally activates the heaters when the ambient temperature is 40°F or less. The heating process We do not use heaters on our fixtures 65% We have heaters on all fixtures 23% We have fixtures both with and without heaters 12% Do your LED light fixtures contain heaters (Arc c kits)? Figure 34. Heater usage on airfields.

Operation Considerations 49 for an LED light fixture is based on temperature, rather than a function of intensity setting (as is the case for an incandescent fixture). The heating process allows the heater to turn on and warm the fixture prior to the ambient temperature reaching the freezing point at any intensity setting. The actual heating element of an in-pavement LED light fixture is next to the lens of the fix- ture. FAA Engineering Brief 67, Light Sources Other than Incandescent and Xenon for Airport and Obstruction Lighting Fixtures, indicates “. . . the main beam light emitting surface temperature must rise a minimum of 15°C after 30 minutes.” This allows for an efficient heating source con- centrated in critical areas with minimal unnecessary heating of the entire fixture. In-pavement light fixture heaters are not integrated with the LED light assembly or the power supply, but are a separate, detachable unit. The exact style and location varies, depending on manufacturer. Figure 35 depicts the heating element and thermostat components that make up an in-pavement light fixture heater. The figure shows a bidirectional two-cord set fixture. Each circuit has a thermostat and a heater associated with it. The heaters for elevated light fixtures can be integrated into the light assembly (see Figure 36) or a separate detachable unit. The exact configuration varies among manufacturers. Heater operation is similar to that for in-pavement light fixtures as outlined in Engineering Brief 67. The heaters provide heat on the globe/lens of the elevated light fixture to melt snow and ice. The exact method of heating and heater should be discussed with the light fixture manufacturer for the particular light fixture. Because the LED heater is thermostatically controlled and is concentrated on the main beam, it is more predictable than its incandescent counterpart and more effective in applying heat to the lens at a lower intensity setting. An incandescent light fixture applies an unregulated amount of heat to its entire surface area. Although the incandescent fixture melts ice and snow, this typi- cally happens at a higher intensity setting than an LED light fixture. Table 3 indicates the typical operating characteristics of an incandescent lamp for an airfield lighting circuit. The table shows that the power consumption of the lamp drops below half from the highest intensity setting to Step 3. One of the objections to the use of a heater is that heaters are often the first component to fail and therefore cause a diminished MTTF to the fixture. Discussions conducted with light Figure 35. In-pavement fixture Arctic kit.

50 LED Airfield Lighting System Operation and Maintenance fixture manufacturers and additional research have indicated the MTTF of the light fixture includes the heater. The failure tests performed by the manufacturers have been on fixtures with heaters, thus the MTTF of the light fixture is not limited by the heater. For example, adding a heater to a runway centerline light fixture does not affect the published MTTF of 150,000 hours. This eliminates the concern of affecting the life of an LED light fixture by selecting one with a heater. Another objection to the use of heaters is the added energy consumption and increased operational energy cost. A calculation was performed using an L-852D LED light with a heater, an L-852D LED light without heater, and an L-852D quartz halogen light, to determine yearly power consumption. The research team assumed a cold-climate airport has, on average, 157 days at 40 degrees and below and 208 days at 40 degrees and above, operates its lights on the highest intensity setting an average of 12 hours per day (see Figure 37), has approximately 500 lights, and pays $0.12 per KWH; the airport could realize energy costs as indicated in Figure 36. Elevated fixture heater and light. Lamp Characteristic for Incandescent Lamps Intensity Level FLA (%) Amps (A) Lumens (%) Watts (%) RW C/L Watts TW C/L Watts LED Heater Step 5 100% 6.60 100% 100% 96W 64 W 32W Step 4 79% 5.21 23% 69% 66.24W 44.16 32W Step 3 63% 4.16 5.7% 48% 46.08W 30.72 32W Step 2 52% 3.43 1.73% 35% 33.60W 22.4 32W Step 1 43% 2.84 0.53% 26% 24.96W 16.64 32W Table 3. Typical lamp operating characteristics for incandescent lamps.

Operation Considerations 51 Fixture Volt-amps (VA) Watt-Hrs/Year Percent Difference Energy Cost L-850D Quartz Halogen 64 46,720 Baseline $2,803.00 L-850D LED W/Heaters 50.8 23,772 50% less than quartz $1,426.00 L-850DA WO/Heaters 18.8 13,724 70% less than quartz 43% less than heaters $823.00 Table 4. Operational energy cost example. Key Takeaways • The use of heaters in LED light fixtures is incorporated in the MTTF of the LED light. • Light fixtures with heaters provide a predictable and efficient heating operation with the heating element focus on the light beam area of the lens. • Precipitation type and snow/ice removal techniques influence the need for heaters, i.e., airports with occasional ice and minimal removal equipment may benefit by having heaters vs. airports that are highly experienced with snow and ice removal. • The study did not produce sufficient data to determine when heaters are needed. • Airports should discuss the type, configuration, and use of heaters with the light fixture manufacturers to determine what is appropriate for use at a particular airport. Table 4. (This number is based on the light fixture load only and does not include transformer losses, CCR efficiency, and additional hours of operation, and the KWH cost at each airport will vary. Regardless, LED light fixtures equipped with heaters provide a substantial reduction of energy.) On average, how oen are your airfield lights illuminated daily? Figure 37. Amount of hours lights are on at airports surveyed.

52 LED Airfield Lighting System Operation and Maintenance Monitoring The two advisory circulars on monitoring AGL systems are AC 150/5345-10, Specification for Constant Current Regulators and Regulator Monitors, and AC 150/5345-56, Specification for L-890 Airport Lighting Control and Monitoring System (ALCMS). AC 150/5345-10 describes monitoring through the constant current regulator and detection of the status of the CCR and the series lighting circuit. Five conditions must be detected, four of which deal with the status of the CCR (i.e., loss of power, input over current shutdown of CCR, drop in output power to series circuit and irregular output current to series circuit). The condition that deals directly with the series lighting circuit is lamps out in the series circuit. AC 150/5345-56 describes monitoring through a lighting control system and discusses vari- ous levels of monitoring, with each level building to the next level. The levels include control and status, basic—monitoring of circuits and feedback, and advance—monitoring of lamps out for low visibility operations. Advance monitoring indicates the quantity and location of non- operational fixtures in a particular lighting system to help ensure compliance with low-visibility requirements. The survey data suggests issues seem to rise as a result of the calibration of CCRs for the lamps- out monitoring of light fixtures. The initial generation of LED light fixtures had compatibility issues with the lamps-out monitoring system. Typically, for an incandescent light, a burnt-out lamp would cause an open circuit on the secondary side of the isolation transformer, thus allowing the transformer to become saturated. A saturated transformer appears as a shorted circuit in the series circuit, thus significantly reducing the impedance of the isolation transformer and the fixture. Cali- brated monitoring systems can detect these changes of impedance in the series circuit, which can be used to determine the number of lamps out. When LED light fixtures, which contain electronics, fail, they typically continue to draw some current and load. This condition may not change the impedance of the circuit significantly enough, thus rendering the monitoring system unreliable. L-829 CCR monitoring of LED light fixtures is being addressed by light fixture manufacturers. Newer generation light fixtures can mimic a burnt-out lamp indication. The newer fixtures contain intelligent power supplies equipped to create an open circuit if an LED array or an elec- tronic component fails. The L-829 monitoring of LED light fixtures can only be accomplished if the circuit is composed of all LED lights of the same manufactured generation or ones that provide the same type of indication. Given that how this is accomplished is subject to the fixture manufacturer’s design preference, airports should verify this capability for their light fixtures with the manufacturer. The L-890 ALCMS provides more advanced monitoring required for low-visibility lighting systems. The monitoring method, configuration, and capabilities for the L-890 system vary by manufacturer, so airports should discuss specifics with the manufacturer. The control and monitoring for the L-890 system can be accomplished by adding a control and monitoring unit (CMU) to the input of a light fixture and communicating with the head-end equipment via power line signal over the circuit power feeds. Another version of the L-890 control and monitoring system uses a programmable logic controller (PLC) base system communicating via a fiber-optic cable. Both systems interface with the input of the fixture and rely on electri- cal measurements to provide data to the controller. The systems face similar issues because of their reliance on electrical measurements. Airports surveyed used both these systems. In gen- eral, the survey data and case studies indicated a mix of responses as to how this system works with LED light fixtures. Some airports have implemented LED light fixtures on low-visibility

Operation Considerations 53 Photometrics and Chromaticity Photometrics Tables 1 and 2 in AC 150/5345-46, Specification for Runway and Taxiway Light Fixtures, indi- cate the photometric output requirement for in-pavement and elevated AGL fixtures. Each type of light fixture has a specific requirement and curve for photometric output. These tables do not distinguish between LED and incandescent light fixtures and, therefore, they have the same photometric output requirement. The requirements for in-pavement lights are based on the projection of the main beam curve and the surrounding 10% beam curve (as illustrated in Figure 38). Using Figure 38 for an L-850A runway centerline light fixture, the main horizontal beam ranges from -5° to +5° and the main vertical beam ranges from 0.2° to 9°. This main beam at the highest intensity setting has a minimum average intensity of 5000 candelas measured at 1 degree intervals along the main axis. The main beam is above the horizontal axis of the light fixture and provides a complete forward projection of the light. The photometric output has an additional FAA requirement—the 10% beam curve. The 10% beam curve for the example of a runway centerline light fixture envelopes the main beam and Key Takeaways • Verify with a light fixture manufacturer the capability of their light fixtures for use with L-829 and L-890 monitoring systems and calibrate accordingly. • Be careful when performing L-829 monitoring on a circuit with various manufacturers’ light fixtures installed. Verify the method of indication for each type of light fixture with the manufacturer. lighting systems (e.g., runway guard bar lights and controllable stop bars), while others choose to use incandescent light fixtures for these systems to ensure reliability. Based on the survey, no direct conclusion can be drawn about the effective operating capability of LED light fixtures on monitored circuits. Control and monitoring issues are being addressed with intelligent power supplies in the newer generation of light fixtures, thus allowing the use of LED light fixtures on low-visibility systems. Caution should be taken in mixing manufacturers’ LED light fixtures on a monitored circuit. LED light fixtures from one manufacturer may not be compatible with the monitoring configuration of another manufacturer’s L-890 control and monitoring system. Airports with lamp-out monitoring generally rely on visual inspections and have de-emphasized the use of remote monitoring solely. If L-829 or L-890 monitoring is being used and LED light fixtures are being installed, the research team recommends discussing the airport’s unique monitoring needs and requirements with a light fixture manufacturer and investigating the method and capabili- ties of their control and monitoring system for LED light fixtures.

54 LED Airfield Lighting System Operation and Maintenance has a horizontal beam ranging from -7° to +7° and a vertical beam ranging from -4° to +13°. The intensity of the 10% curve must be no greater than 10% of the main beam average, or 500 candelas. Additional requirements include (1) no value inside the main beam ellipse must be less than 50% of the main beam average and (2) the maximum candela value divided by the minimum candela value must not be less than 3. These requirements are designed to eliminate a bright spot in the ellipse. The 10% beam curve indicates the beam pattern with negative values below the horizontal of the fixture—This light, seen reflecting on the horizontal surface of the fixture, is an inherent characteristic of a light beam ellipse shape. The photometric requirement for LED light fixtures and incandescent light fixtures are the same. Different fixtures (e.g., runway edge lights, runway centerline lights, and taxiway center- line lights) have different requirements based on use. One of the original problems with LED light fixtures was that light intensity output did not fol- low the compatible incandescent light fixture light intensity output at the intermediate steps. This resulted in an uneven light output among different light fixtures along the intermediate opera- tional intensity settings. The uneven light output affected the operational capability of the light fixture during various visibility conditions that used the intermediate step settings of the circuit. In response to this, the FAA updated Engineering Brief 67, Light Sources Other than Incandes- cent and Xenon for Airport and Obstruction Lighting Fixtures. This update supplied specific cri- teria for the minimum and maximum photometric intensity of the LED light fixture along each intensity setting. The new requirement demands that the intensity follow a smooth curve mim- icking that of an incandescent light fixture. Figures 39 and 40 show the minimum and maximum percentage of intensity output for LED light fixtures. Light manufacturers revised their LED light fixtures in subsequent generations with the implementation of this Engineering Brief update. Engineering Brief 67 was developed in 2000 Figure 38. Light fixture photometric ellipse.

Operation Considerations 55 Figure 39. LED fixtures dimming curve for white LED. Figure 40. LED fixtures dimming curve for color LED.

56 LED Airfield Lighting System Operation and Maintenance Figure 41. CIE mixture diagram. and was updated in 2012 (revision D) to revise the dimming curve. The survey data indicates that LED lights are operating in accordance with the requirements and that this issue has been resolved. Chromaticity Chromaticity is the quality of color characterized by its dominant or complementary wavelength and purity measurements. The aviation industry basis of color for lighting systems is found in Aerospace Standard AS25050, General Requirements for Colors, Aeronautical Lights and Lighting Equipment. Figure 30 is the International Commission on Illumination’s (CIE’s) mixture diagram, which indicates color limits for the aviation lights. Figure 41 illustrates the aviation color wave- length limit. The FAA has refined the boundaries as more stringent than the diagram indicates, but given the scale of the diagram it could not be displayed accurately. This diagram will serve as a representation for example purposes. The section for aviation green, which has the largest wavelength variation, any type of light that falls within this area is considered compliant. To better understand, the next step is to superimpose the color spectrum onto this figure. Refer to Figure 42. The overlay of the color spectrum on the mixture diagram provides perspective on the allowable color range for aviation lighting. In Figure 42, a border was drawn around the aviation green and aviation blue areas. The area for aviation green is large, ranging from blue/green to pure green.

Operation Considerations 57 Figure 42. Color spectrum overlaid on mixture diagram. Table 5 details the color location of an LED taxiway centerline light fixture and Table 6 details the color location of an incandescent taxiway centerline light fixture. The first column in each table represents the light beam angle position of the location measurement. Referring to the ‘X’ and ‘Y’ coordinates, the color locations are relatively consistent throughout the various angles. Taking the location of the first row for both Tables 5 and 6 and plotting this onto Figure 41 results in the color location of the taxiway light fixtures as shown in Figure 43. The incandescent light fixture color is near the bottom of the green spectrum, where the color transitions to blue. To the human eye, the light appears greenish-blue. The LED light fixture is near the top of the green color spectrum and thus provides a truer green color. The difference in color location of these two fixtures makes an LED light fixture appear brighter than an incandescent light fixture. This typically leads to the conclusion that the LED is not oper- ating properly. However, based on the allowable color spectrum, both light fixtures comply with FAA requirements. The other light fixtures have a smaller color spectrum range, so their color location differences will not be as great, so the colors between the LED and incandescent light Position Degrees X Y (-3.5,1) 0.177 0.730 (-3.5,8) 0.178 0.730 (3.5,1) 0.174 0.732 (3.5,8) 0.174 0.737 (0,4.5) 0.176 0.733 Table 5. LED taxiway centerline light color location. Position Degrees x y (3.5L, 4.5U) 0.1622 0.3960 (0H, 4.5U) 0.1620 0.3929 (3.5R, 4.5U) 0.1626 0.3970 (0H, 1U) 0.1641 0.3940 (0H,8U) 0.1614 0.3988 Table 6. Incandescent taxiway centerline light color location.

58 LED Airfield Lighting System Operation and Maintenance fixtures for blue, white, yellow, and red will appear similar. Because the light color locations may vary for the different types of LEDs used by the manufacturers, the color may vary among differ- ent light manufacturers light fixtures. It has been reported that taxiway LED fixtures appear brighter than their counterparts, and pilots have requested they be set to a lower intensity setting. However, this does not suggest the fixtures are out of FAA compliance but this is just one of the differences with LED light fixtures. Ultimately, the pilots are the users of the system and the system should be operated to accommodate their needs. Key Takeaways • Using a five-step intensity setting CCR for taxiway centerline LED lighting systems is recommended. This will allow lower intensity settings to be set at verbal request. • Verify color coordinates and color spectrum among LED light fixtures of different manufacturers if adding to an existing LED light circuit or location. Colors located close to each other will provide consistency in the lighting system. • Do not mix LED and non-LED light fixtures on straight sections of taxiway or on a runway because of chromaticity compatibility as described in AC 150/5340-30. Return on Investment Discussion Among the airports surveyed, the greatest concern about LED lighting was cost. Roughly 75% indicated the cost of LED lighting prevents them from installing and/or adding LED lighting on their airfields. However, the data also suggests LED lighting on airfields accounts for 20% to 50% of total lighting at most airports. Understanding the Return on Investment (ROI) for LED lighting compared to non-LED lighting will help airport decisionmakers select the best course of action for their airports. Figure 43. Color location of the taxiway light fixtures.

Operation Considerations 59 Factors to consider when determining ROI compared to non-LED fixtures include • Fixture cost • Energy cost (with and without heaters) • Maintenance cost (lamp replacement labor and materials) • Refurbishment cost • Fixture damage rates • Failure rates LED fixtures have a higher initial cost to purchase than incandescent fixtures (Figure 44). Airports will have a higher initial investment cost for material, requiring upfront capital and relying on ROI to balance investment. Historical energy cost data should be considered to deter- mine if cost is a driver for the use of LED fixtures with or without heaters. Incandescent fixtures have a labor and material lamp replacement cost associated with them that should be consid- ered. Refurbishment of light fixtures are similar for both type of fixtures and should not affect ROI. Because LED fixtures have a higher replacement cost (given damage caused by snow plow operations and vehicles), airports need to consider fixture replacement as part of their ROI. LED fixtures have a longer MTTF, thereby minimizing routine maintenance costs which could greatly affect ROI. Energy cost and maintenance cost have a major effect on ROI. Reduced energy consumption is evident when using LED light fixtures and depends on energy costs, equipment efficiencies, operation of the system (light intensity settings), and state of repair of the system. The energy cost reduction varies from region to region and airport to airport. The most significant issue affecting the ROI is maintenance cost. To maximize the ROI, main- tenance costs must be minimized. The best way to minimize maintenances costs is to use fixtures that require less maintenance because this minimizes runway shutdowns and labor required to replace the fixtures. The following example illustrates the factors that affect maintenance costs. Table 7 summa- rizes the factors affecting ROI for a 100-fixture LED Runway Guard Light (L-852G) circuit versus an incandescent light fixture. This demonstration indicates the effect lamp failure has on maintenance costs for one circuit, over the lifetime of the circuit—in this case, 15 years. What is prevenng you from installing more LED light fixtures at your airport? Figure 44. Survey results show cost as leading obstacle for acquiring more LED fixtures.

60 LED Airfield Lighting System Operation and Maintenance With MTTF as a large component of ROI, the defining factors that affect MTTF must be evaluated for both LED and incandescent light fixtures. Historically, the discussion of fixture performance has centered on whether the fixture is ener- gized and operating or not. The simplest definition of failure is that there is no light coming from the fixture. However, for in-pavement systems (and especially CAT II and III) lighting systems, a paradigm shift is warranted to understand the true definition of fixture performance. Three factors affect the operational performance of a light fixture: lamp life, photometric output, and deterioration of optical lens. The three factors are summarized in Table 8. The MTTF for an LED fixture includes all components (i.e., LED light assembly, power sup- ply and heater, if applicable). Taking the typical operating conditions and assuming a 10-hour operational period per day, the proposed MTTF for an LED is 20 years and that of an incan- descent is almost 2 years. Once the photometric output of a fixture drops below 70% of the required output, the fixture is deemed noncompliant. For an incandescent fixture, this 70% deterioration can occur within 50% of its operating life, thus reducing its MTTF to 1 year. An LED fixture has minimum light output deterioration, allowing it to operate within the compli- ant range for most its life. The third factor, deterioration of the optical lens, which includes pitting, scratching, rubber removal damage, depends on the environmental condition (not the light fixture type). So as a comparison of lights and their MTTF: MTTF Ignoring Photometrics: 150,000 6,000 25 MTTF of LED Fixtures MTTF of Incandescent Fixture Times= = The LED has a 25 times greater lamp life expectancy than an incandescent. Taking the deterio- ration of the photometric output into consideration, the LED has a 32 times greater overall life expectancy. Factors LED Incandescent MTTF Average LED life of 56,000 hours under high-intensity conditions and more than 150,000 hours under typical operating conditions. Low-energy/long-life halogen lamps are 48W with a rated life of 1,500 hours at 6.6A and in excess of 6,000 hours in practical use. MTTF to Photometric Output Dips Below 70% Approximately the life of the fixture. Photometric Intensity of the Quartz lamp may drop below 70% at 50% of the life of the lamp. Deterioration of Optical Lens and Environmental Factors Subject to deterioration is the same for either type of fixture. Subject to deterioration is the same for either type of fixture. Table 8. Operational performance factors. Category of Cost Percent Savings Costs Energy Cost 4.2% $3,521.52 Lamp Replacement Labor Cost 71.0% $60,000.00 Material Cost 24.8% $21,000.00 Table 7. LED maintenance cost savings.

Operation Considerations 61 Key Takeaways • Develop a maintenance plan that includes cleaning and inspect- ing the lens and performing photometric testing. • Develop a lens cleaning and/or replacement program. Lenses will pit over time which will affect light output performance, thus reducing MTTF. • Track fixture maintenance and replacement to help determine associated maintenance costs. • Develop a commissioning and final acceptance plan that ensures that the elevation and alignment of the light base and fixture is correct so as to ensure that any future deterioration is the cause of environmental factors rather than poor installation. MTTF with Photometrics: 10% 30% 135,000 4,200 32 MTTF of LED Fixtures Photometric Drop MTTF of Incandescent Fixture Photometric Drop Times greater ( ) ( ) = = However, both types of fixtures are subject to lens pitting, rubber removal damage, snow plow damage, and other environmental factors. To maximize the MTTF and get the true per- formance out of the LED lights, and thus the appropriate ROI from LED, the airport has to consider a maintenance approach that includes all of the above factors. Case study discussions indicated that most maintenance is performed based on whether or not a fixture is operating (light output). However, operating in this fashion provides a false sense of fixture longevity for incandescent light fixtures. Light output and lens deterioration need to be addressed as part of maintenance practice.