LED external lighting solutions have been embraced to a large extent in both commercial and business aircraft. We have reached out to industry experts to assess how LED exterior lights are tested to evaluate if they are degrading and the repair process for when they are not working.
LED degradation is mitigated through careful selection of the LED type during the design process, then, during the design and qualification phase of a new LED exterior light product, multiple sample units are tested in extreme environmental conditions beyond those experienced in the flight envelope, explains Heads Up Technologies. “We perform highly accelerated life testing (HALT) to improve product reliability and quality during the product development cycle. HALT identifies product design and manufacturing related failure mechanisms by exposing the product to ever increasing environmental conditions - e.g., temperature, vibration, electromagnetic interference,” says Heads Up Technologies. “If the product fails during HALT, weaknesses are identified, root causes determined, and corrective action implemented, resulting in improved reliability and quality of the LED light. When a light is not working in the field, a simple remove and replace activity can be performed. The unit in question can often be repaired by the manufacturer to reduce the cost impact of failures,” Led Surgical Lights
LED exterior lights undergo various tests to assess their degradation over time and there are some common methods for making this assessment, affirms John Fogel, product manager at Amglo. “The first is the lumen maintenance testing that measures the light output (lumens) of the LED over a specified period. The LED is typically operated continuously, and its light output is measured at regular intervals. By comparing the initial light output to the output after a certain period, the rate of lumen depreciation can be determined,” he says. “LEDs are also sensitive to temperature, and excessive heat can accelerate degradation. Temperature testing involves subjecting the LED to different temperature conditions, both high and low, to assess its performance and degradation, the extreme temperature cycles can help simulate real-world operating conditions and assess the LED’s durability.”
Other methods to assess degradation are environmental testing and aging testing, explains Fogel. “LEDs used in exterior lighting undergo various environmental tests to evaluate their resistance to factors such as moisture, humidity, dust, vibration, and shock. These tests ensure that the LED can withstand the harsh conditions experienced during aircraft operations and maintain its performance over time,” he says. “LED aging tests involve subjecting the LED to accelerated aging conditions, such as operating it at high currents or exposing it to high temperatures. These tests simulate the long-term effects of usage and help assess the LED’s degradation rate and performance under stress.”
Photometric testing measures various characteristics of the LED’s light output, including luminous intensity, light distribution, color temperature and color rendering index (CRI), and, by periodically testing these parameters, any changes or degradation in the LED’s performance can be detected. “Lastly, reliability and endurance tests involve subjecting the LED to long-duration operation under normal or accelerated conditions to assess its reliability and endurance. The LED is monitored for any changes in light output, color, or other performance parameters”, he says.
LED lights are endurance tested first on LED component Level and later in the application on Light fixture level to standardized test methods, affirms Andre Hessling, principal fellow at Collins Aerospace – Interiors. “The primary standard is the IES LM-80-20 approved method, measuring luminous flux and color maintenance of led packages, arrays, and modules. These endurance tests run for a minimum of 6000h which then allows predictions of performance degradation. Many modern lights also have closed loop flux output monitoring to compensate for light losses over time or indicate when the Unit no longer meets specification,” he says.
The tests are conducted in accordance with industry standards and specifications, such as those set by the Federal Aviation Administration (FAA) or international organizations like the International Electrotechnical Commission (IEC). “By conducting these tests, manufacturers can ensure that LED exterior lights meet the required performance standards and have minimal degradation over their operational lifespan,” affirms Fogel.
As to the repair process for when LED exterior lights are not working, in most cases the operator or airline will just replace the failed lamp, observes Fogel. “However, if they were to go through a repair process for non-working LED exterior lights it would most likely involve diagnosis, troubleshooting, component replacement, repair or re-soldering, testing and verification, and installation and re-assembly,” he says.
Maintenance of LED lights is typically more involved than with other light bulb-based fixtures as the LED control, monitoring and heat dissipation requires a specific LED PCB that would need to be replaced on shop level, explains Hessling. “Most LED units should be maintenance free for more than 20,000 flight hours instead of hundreds of hours compared to conventional lights,” he says.
Concerning diagnosis, the first step is to identify the specific issue causing the LED light to malfunction, according to Fogel. “This can be done through visual inspection, testing the electrical connections, or using diagnostic tools to check for any faults or errors,” he says. “Once the problem is identified, troubleshooting is performed to determine the root cause. It may involve checking the power supply, circuitry or components associated with the LED light. This step helps narrow down the issue and ensures that the correct repair approach is undertaken.”
If a specific component is found to be faulty, it needs to be replaced, affirms Fogel. “This could involve replacing a burned-out LED chip, a malfunctioning driver, or any other defective part, he explains, the replacement component should be of the same specifications and compatible with the LED light,” he says. “In some cases, the issue may be related to lose or damaged connections. In such situations, the faulty connections are repaired or re-soldered to ensure a proper electrical connection. After the repair or component replacement, the LED light is tested to ensure it is functioning properly and this may involve connecting it to a power source and measuring the light output, checking for any flickering or abnormal behaviour, and verifying that all features and functions are working as intended.”
Dental Chair Bulb Once the repair is confirmed successful, the LED light is re-installed in its original position or fixture, any disassembled parts are reassembled carefully, ensuring proper alignment and secure attachment, declares Fogel. “It is important to note that the repair process may vary depending on the specific design and construction of the LED light. In some cases, it may be more cost-effective or practical to replace the entire LED light fixture rather than attempting repair, especially if the damage is extensive or the light is outdated,” he concludes.