Student Member, IEEE
, Kam-Chuen Yung,
, and Michael Pecht,
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20740, USA
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
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.
IndexTerms —Phosphor-converted white LED, chromaticity state shift, prognostics, qualification testing, unscented Kalman filter (UKF).
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