Multi-Domain Model for Predicting Aging in Phosphor-Converted White LEDs with a Mix of Multiple Phosphors

In the past decade, increasingly accurate multi-domain models have been developed to describe the operation of high-performance light-emitting diodes (LEDs), which now dominate most lighting applications. Although these models reproduce the behavior of new LEDs with high fidelity, their applicability remains limited by the lack of mechanisms to account for degradation processes. In this article, we present an extension of the Delphi4LED multi-domain LED model that accounts for the aging of phosphor–converted white LEDs containing multiple phosphor materials. As a case study, we modeled a mid-power LED with a moderate lifetime, subjected to aging conditions that extend beyond those required by industry-standard LM80 tests. For the investigated LED device (Refond W40QI35DS-DF-J-Y), our results indicate that the aging in the electrical characteristics can be effectively modeled by an additional series resistance caused by accumulated forward-current stress. In terms of the light output characteristics, the multi-domain model is completed with a model of multiple independently degrading phosphor layers. The degradation of each phosphor component is modeled as a temperature- and flux-dependent process. The proposed model shows good agreement with experimental results: the deviations between model and measurement results are of the same order of magnitude as the scatter of the test results obtained for different samples under identical aging conditions; both are in the range of 3%–7% on average. Furthermore, the model accurately predicts changes in the LEDs’ electrical and optical characteristics, maintaining small deviations between measurements and predictions for a forecasted aging period of up to 3.75 times the length of the physically elapsed aging time, i.e. when parameter extraction is based only on data obtained during the initial 1,343 hours of aging and used to forecast LED aging up to 5,040 hours. We also demonstrate that the model remains valid even when environmental conditions change over time, allowing it to be used as a true digital twin of the specific LED package that also accounts for aging.