Highly accelerated life testing of LED luminaries

With rapid development of lighting emitting diode (LED) market, more people are focusing on reliability testing method of LED luminaries system. Based on the previous exploration, to assess the whole system reliability with a fast way, authors propose to divide the system into several subsystems, and then carry out step stress accelerated testing (SSAT) to get failure mechanism and reliability distribution of each subsystem, finally calculate the life distribution of the whole system by combining with system statistics analysis methodologies. The first step, the most important step, is to know the stress limit of the subsystem before conducting SSAT testing. The intention of normal highly accelerated life test (HALT) process is to subject the item under test to stimuli well beyond the expected field environments to determine its operating and destruct limits, but without enough attention on those degradation parameters of products, especially like LED products which present their life characteristics on many output parameters, such as lumen maintenance, color rendering index (CRI), chromaticity coordinate, junction temperature and optical efficiency, which included important life information. Therefore, Focused on the LED light source subsystem, it is not practical to accelerate it with HALT by only focused on failure or destructive data. In this paper, different HALT procedure with different objects is introduced, and two types of LED system from separated vendors are conducted proposed HALT before SSAT testing. Test results suggested that it is feasible to observe output parameters of LED products to decide the stress limitation during HALT testing, pseudo junction temperature and Lumen maintenance can be regarded well as key parameters. For other parameters of system, different parameter has changed with different rule, which indicates that key concerned factor should be fixed. Meanwhile, it is found that the lumen maintenance decreases very fast when temp stres- over 110 °C. When focused on some failure mechanisms without change even if overloading the stress, a good solution for a fast qualification method will be worked out. Deep study on this found should be carried out in future.