High power light-emitting diode (LED) has gained more and more applications because LED has many advantages over traditional light sources. However, it is extremely time-consuming and complicated to evaluate the LED luminaires reliability, in particular, the luminous degradation. In this work, a novel hybrid method, which combines the thermal modeling and temperature measurement, is proposed to estimate the junction temperature of high-power LEDs at system level, and therefore predict the lifetime of LED luminaries based on the known LM-80 data. First, a reference point at a luminaire system is selected to measure the temperature in the operating mode. Secondly, thermal modeling is performed to predict the reliable relationship between the junction temperature and the temperature of reference point (measuring point). Finally, the relationship between lifetime and junction temperature provided by the known LM-80 database is applied to estimate the LED luminaire's lifetime. To validate the predicted junction temperature, the thermal measuring experiments combined with the thermal tester T3ster are also implemented in this paper. It is found that, after a luminaire operates to a steady situation, the temperature difference between the reference point and the junction point reaches a constant, which indicates the thermal resistance between them can be simplified as a stable value. Therefore, the junction temperature of a luminaire can be obtained based on the temperature measurement of a measuring point and the thermal modeling. The lifetime predicted with the proposed method meets closely the lifetime estimated by vendor. The proposed method is expected to be very useful in future LED luminaire qualification test specification, instead of running lumen maintenance test to extrapolate the lifetime.
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