LED lighting system reliability evaluation criteria
LED lighting products used in general lighting for at least 10 years, but how to assess the reliability of LED lighting products is still a topic of endless debate, and sometimes even quite confusing. This article will discuss some of the LED lighting system reliability evaluation criteria and process.
The performance of incandescent or fluorescent lamps using existing lighting technology is usually measured by the average service life, which refers to the time it takes for half of the lamps under test to fail (no longer emit light). The average life of an incandescent lamp is about 1000 hours, the average life of a compact fluorescent lamp is about 12,000 hours, and the average life of a linear fluorescent lamp is about 25,000 hours. In contrast, LEDs that operate under the right conditions can emit 100,000 hours or more and can not measure their average lifetime.
LED lighting life L70 indicators to characterize, refers to the lumens (L) measured the output light intensity dropped to 70% of the initial brightness of the time spent. From the standpoint of reliability engineering, the L70 has the disadvantage that the measurement method published by Lighting Association, a recognized authority in lighting, measures only the lumen output of the LED package without incorporating any other system factors such as driver circuit, thermal management design, and even optical path Consider it. Today's lighting manufacturers are not focused on the reliability of the entire system, because the lights are almost always the first to go bad. But as LED lighting has evolved, manufacturers and end-users have come to realize that other parts of the lighting system can become a limiting factor in overall lifespan.
Reliability refers to the probability that a part or a system will work as intended under certain conditions of operation for a specified period of time. Product reliability assessment is basically based on accelerated life test statistical modeling and prediction methods. For LED lighting systems, rated light fades and other component failures can affect overall reliability, as shown in Figure 1. The statistical models that proved to combine these two different factors of lighting system performance have not been well-suited, which is why the focus has always been on robustness testing.
In field operations, robustness is a non-quantitative measure of the ability of a product or system to function as envisioned in a given environment by confirming that products made to a particular design and manufacturing process can withstand more than normal Greater stress under working conditions. For decades, the electronics industry has been using robust test protocols as part of its validation process. Until recently, this concept was accepted by more LED lighting organizations because they finally realized that LED-based lighting products and other electronic products are not much different.
Unlike reliability tests that use design prototypes, robustness tests typically put manufacturing samples under a variety of over-stress conditions, making them more effective part of the overall quality certification system. In contrast, the goal of reliability testing is to detect a failure to understand the failure mode. What the robustness test expects is that all products will work properly at the end of the test.
The robustness test of LED lighting is very similar to the test of other types of electronic equipment released by JEDEC, IEC and other organizations, but some adjustments are made according to the particularity of LED products. The test scenario for a given product will vary depending on the target application, such as test panels for indoor office products that may not need to contain high temperature work or vibration. The table below lists the more common robustness tests recommended for LED lighting products.
Some recent standards bodies have studied the robustness of LED lighting systems and much remains to be done. Next time we discuss existing and planned standards and how they address the reliability issues of LED lighting systems.