Abstract
The lifetime prediction using accelerated degradation test (ADT) method has become a main issue for white light emitting diodes applications. This paper proposes a novel lifetime model for light emitting diodes (LEDs) under thermal and electrical stresses, where the junction temperature and driving current are deemed the input parameters for lifetime prediction. The features of LEDs’ lifetime and the law of lumen depreciation under dual stresses are combined to build the lifetime model. The adoption of thermal and electrical stresses overcomes the limitation of single stress, and junction temperature in accelerated degradation test as thermal stress is more reliable than ambient temperature in conventional ADT. Furthermore, verifying applications and cases studies are discussed to prove the practicability and generality of the proposed lifetime model. In addition, the lifetime model reveals that electrical stress is equally significant to the thermal stress in the degradation of LEDs, and therefore should not be ignored in the investigation on lumen decay of LEDs products.
Highlights
White light emitting diodes (LEDs) is proverbially acknowledged as the most promising energy saving solution for lighting applications due to its high efficiency and long lifetime [1]
Some essential and superior methods were developed to help people have a deep understanding on the nature of reliability of LEDs [8,9], such as the photoelectrothermal (PET) theory for LED systems [10,11,12], the degradation of silicone in white LEDs during operation [13], the degradation mechanism of silicone glues [14] and the coupling effects of both LED and driver’s degradations [15]
As has been reported in the literature [31], Wang et al designed five sets of thermal and electrical stress levels to conduct accelerated degradation testing for LED-based light bars, where the junction stress levels to conduct accelerated degradation testing for LED-based light bars, where the junction temperature and driving current are designed as accelerated stresses
Summary
White LED is proverbially acknowledged as the most promising energy saving solution for lighting applications due to its high efficiency and long lifetime [1]. Via a boundary curve theory, they proved that the qualification results obtained from the 6000 h test data under 25 ◦ C and 1500 h test data under 55 ◦ C are comparable to each other for a majority of LED lighting products These studies based on CSADT method focused only on single stress and did not build up relationship between lifetime and accelerated stresses. The current CSADT methods are based on the empirical models, of which the parameters were often obtained by curve fitting from experimental data [34] These models conclude the relationship between degradation and operation time, ignoring the loading conditions in the emission profiles [35].
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