Step-stress accelerated testing of high-power LED lamps based on subsystem isolation method

a r t i c l e i n f o Keywords: High-power LED lamp Step-stress accelerated test Subsystem isolation method Lifetime Degradation Mechanism The lifetimes of high-power light-emitting diode (LED) lamps are investigated by step-stress accelerated test. The entire lamp is divided into three subsystems, namely, the LED light source, the driver, and the mechanical fixture. Step-stress accelerated tests are conducted on the LED light source only, which is placed in a thermal chamber and connected to other subsystems outside the aging furnace. Thus, the highest possible stress level can be reached for the LED light source. The reliability characteristics of the LED light source are analyzed based on the step-stress accelerated degradation test model. The fault tree and Monte Carlo algorithm are used to deduce the reliability of the entire LED lamp. The case study shows that the tested samples underwent similar degradation mechanisms under three reasonable stress levels and that the proposed procedure is fast and effective in accelerating the decay process of LED lamps. The predicted LED lamp lifetime is close to the value specified by the LED lamp manufacturer. The proposed subsystem isolation method can overcome the obstacle resulting from the significant difference between the breakdown stress limits of each subsystem. Light-emitting diodes (LEDs) have triggered a revolution in illumination because of its distinct advantages, such as long lifetime, energy efficiency, and low environmental impact. However, when LEDs are subjected to electrical and thermal stresses, the resulting material degradation and structural damage could result in lumen degradation, color shift, or even early decommissioning of LEDs. The reliability of LED products has become a significant concern [1]. The lifetime of an LED lamp is defined by the Illuminating Engineering Society (IES) under the standards LM-79 and LM-80. Similarly, the Energy Star TM-21 procedure specifies the process for lumen maintenance over time with its current input and working conditions [2]. These procedures are time-consuming. LM-80 requires at least 6000 h of testing to achieve reliable long-term predictions. IES LM-84 and TM-28 require a minimum of 3000 h of testing [3]. In recent years, select studies have investigated reliability modeling and lifetime prediction for the LED lamp system. Villanueva et al. [4] presented a reliability testing method for LEDs based on overstress life test method. However, when they attempted to evaluate the reliability of portable lamps, only a few lamps passed the test [4]. Considering the degradation of …