Lifetime evaluation methods for LED products

As a kind of electronic products, the failure rate of LED products follows the traditional bathtub curve. Corresponding to the different regions in the failure rate curve of the LED products, this paper proposes two different lifetime evaluation methods. In the first method, the lumen maintenance lifetime of the LED device is estimated by only considering the failure of lumen maintenance, corresponding to the aging failure stage. The L70 lifetime, indicating the time when the lumen maintenance of the LED product degrades to 70% of its initial value, can be estimated through an accelerated life test with a high temperature stress. Then the L70 lifetime of the LED product under the normal operating condition is calculated based on the accelerated test data by using the degradation coefficient method. It is shown that a suitable temperature stress in accelerated test will not create other failure modes in the test LED lamp, and therefore can reduce the test time to estimate the mean replacement period of a batch of lamps. The other method is proposed in correspondence to the accidental failure stage of the LED product. In this case, it is assumed that the lifetime of the LED product follows an exponential distribution. Then the average life expectancy under the normal operating condition, mean time to failure (MTTF) of LED devices and not repairable lamps can be estimated from the point estimates and confidence intervals from the experimental data of certain reliability tests. From the experimental results, it is proved that more accurate reliability and lifetime expectancies of both the LED devices and products are addressed from the point estimates and confidence intervals calculations.