IEEE Transactions on Device and Materials Reliability, Vol. 14, No. 1, pp 564-573, March 2014, doi:10.1109/TDMR.2013.2283508

Prognostics of Chromaticity State for Phosphor-Converted White Light Emitting Diodes Using an Unscented Kalman Filter Approach

Jiajie Fan, Kam-Chuen Yung and Michael Pecht
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland


Phosphor-converted white light-emitting diodes (pc-white LEDs) utilize a blue LED chip converted by the phosphor to obtain white light emission. Pc-white LEDs have become one of the most popular white LEDs. The reliability concerns of pc-white LEDs involve both lumen maintenance and chromaticity state. However, previous research on the health of LEDs has not taken chromaticity state shift into consideration. Therefore, this paper investigates the chromaticity state shift of pc-white LEDs during an ageing test using a data-driven prognostic approach. The chromaticity coordinates (u', v') in the CIE 1976 colour space are used to define the states of chromaticity. The Euclidean distance measures between two different chromaticity states represent the chromaticity state shift of LED after ageing. A non-linear dual-exponential model is selected to describe the chromaticity state shift process. Usually, the LED industry used an extrapolating approach to project future states of LED lighting sources, which relies on the non-linear least square method to fit the obtained data and extrapolates the fitting curve to get the future state. In this paper, a recursive non-linear filter (an unscented Kalman filter) is used to track the future chromaticity state. The result shows that the unscented Kalman filter approach can improve the prognostic accuracy more compared with the conventional extrapolating approach.

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