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

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 aging test using a data-driven prognostic approach. The chromaticity coordinates (u^´, v^´) in the CIE 1976 color 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 aging. A nonlinear 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 nonlinear least square method to fit the obtained data and extrapolates the fitting curve to get the future state. In this paper, a recursive nonlinear 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.