LED has the features of long life, but with the different working condition and drive current, its life will be different, but generally the life will be around 50K hours. Differ from the traditional lightsource, LED light will decay gradually rather than extinguish instantly. According to the standard IES-LM-80, IES-LM-82 and TM-21, the requirements of the test cycle is generally 6000hr, and it introduced the conception of L70, L50 and etc., which is, L70 (hour): time to 70% lumen maintenance; L50 (hour): time to 50% lumen maintenance.
However, under the increasingly intense price competition of LED market today, it can not meet the requirement of LED application plants for such time-consuming testing process. Now, we will explore how to make a judgment on a LED performance in the shortest possible time, ie. to explore a low-cost, fast and effective method to select LED particles. The main raw materials of LED are packaging glue, gold thread, chips, solid crystal plastic and holder. Each material will directly affect LED performance. We usually use the following three steps to test:
1) Testing initial photometric and electrical parameters of LED particles, including the data under different parameters, the chip size and so on. For this part testing, we recommend Lisun LPCE-2(LMS-9000) Integrating Sphere Spectroradiometer LED Testing System, for identifying the performance of single LEDs and LED lamps. According to CIE127-1997, IES LM-79-08 and IES LM-80-08, it recommends to using an array spectroradiometer with integrating sphere to test SSL products. The LPCE-2(LMS-9000A) also can do the LED optical maintenance test such as Flux VS time, CCT VS time, CRI VS time, Power VS time and so on which is meet LM-80. It can test LED lamps for CCT, CRI, Spectrum, Lumen, lumen efficient, power, power factor, current and voltage and so on, which is meet LM-79.
2) Rapidly aging at room temperature and 1.5 times rated current. Taking 5pcs samples ( can take more pcs if conditions permitted), rapidly aging at room temperature (25 ℃) and 1.5 times rated current (225mA), testing at 0hr, 48hr, 96hr, 168hr four stages for photometric and electrical parameters, and to calculate the attenuation ratio of each node according to the change amount of flux, and to simulate the life curve of LED particles, which shows as below:
3) Rapidly aging at 85℃ and nominal current. Taking 5pcs samples ( can take more pcs if conditions permitted), rapidly aging at 85℃ and nominal current (15mA), testing at 0hr, 48hr, 96hr, 168hr four stages for photometric and electrical parameters, and to calculate the attenuation ratio of each node according to the change amount of flux, and to simulate the life curve of LED particles, which shows as below:
Through the above discussion, we can conclude the fast selecting LED method which is suitable for LED application plants, ie. after got many LED samples from packaging factory, we can disassemble the LED first, to measured the LED chip size. Generally, the bigger size chip is, the greater abilities of anti ESD, anti large current capability will have. Secondly, rapidly aging at room temperature and1.5 times (or double), and then at 85℃ and nominal current. Then, to draw the estimated life according to the flux attenuation ratio of each node at 0hr, 48hr, 96hr, 168hr. Comparing LED luminous flux maintenance rate capability of different manufacturers, to judge pros and cons of them. And finally can choose the most cost-effective LED particles in the shortest time by evaluating LED unit price of different manufactures.