Lumen degradation is a common failure mode in white LED light sources. Lumen maintenance life, defined as the time when the maintained percentages of the initial light output fall below a failure threshold, is a key characteristic for assessing the reliability of white LED light sources.
Most widely studied among various reliability tests for LEDs has been thermal degradation because heat is known to be one of the main factors affecting the LEDs performance and durability. However, the effect of humidity on LED lifetime is also important as many high-power LEDs including street lamps and floodlights are used in outdoor conditions with high humidity.
Ri Pyong Sol, a section head at the Faculty of Electronics, has conducted research into the reliability of high-power white LEDs. He aimed to predict the rated lifetime and to estimate the reliability of 50W white LEDs using their degradation data so that he could find an available method for testing the accelerated life of 50W high power white LEDs.
According to his research results, the relative error in the predicted value of lifetime by temperature accelerated test is 17.4%, which is 4.1% greater than that by temperature-humidity accelerated test.
By his method, the rated lifetime of LEDs can be predicted quite accurately within one day at the scene of high-power LED production.
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