Photometric Testing of Light Emitting Diode (LED) Approach Lighting Systems
SST provides engineering and technical support services to the FAA’s Navigation and Landing Branch at the William J. Hughes Technical Center (WJHTC). The WJHTC is the nation’s premier federal aviation laboratory for advancing the United States National Airspace System (NAS) and sustaining its continued safe and efficient operations. SST’s primary mission supporting the Navigation and Landing Branch is the test and evaluation of new or modified navigation and approach lighting systems prior to their use in the NAS.
In an effort to comply with Federal mandates, modernize equipment, and reduce waste, the FAA is replacing many of the approach lighting systems that currently use incandescent lamps with new Light Emitting Diode (LED) versions. Each of the new LED lamps must be evaluated for proper chromaticity and photometric properties, which determine how pilots perceive the approach lights. These properties determine the apparent brightness, color, and beam spread, which are key for the pilot in maintaining situational awareness. If any of these properties do not meet the requirements, then the apparent differences in color or intensity may cause confusion for the pilot and an increase in workload during a critical phase of flight.
Measuring the chromaticity and photometric properties of lamps to the required precision necessitates a series of specialized test equipment and motion controllers. It also requires a large darkroom in which to make the measurements. Therefore, these measurements are usually made by 3rd party certified testing laboratories, which can be expensive. With many candidate lamps for the FAA to evaluate, SST was able to develop a much more cost-effective solution, potentially saving the Government and taxpayers hundreds of thousands of dollars.
Realizing it would be prohibitively expensive to build and maintain an FAA-owned and operated certified lab from scratch, SST developed the concept to verify the performance of the LED lamps in a two-phased approach. In phase I, SST and the FAA would test the lamps using commercial off the shelf (COTS) test equipment combined with SST developed motion control and data analysis software. Those lamps that passed the initial testing would then be sent to the 3rd party certified test lab for verification of the performance of the lamp in phase II, traceable to National Institute of Standards and Technology (NIST) standards. This avoids the unnecessary costs by having high confidence that the lamps sent for verification will pass the tests.