IEEE Transactions on Industrial Informatics, Volume.10, No.3, pp. 1852-1863, August 2014

Anomaly Detection of Light-Emitting Diodes Using the Similarity-Based-Metric Test

Moon-Hwan Chang, Chaochao Chen, Diganta Das, Member, IEEE and Michael Pecht, Fellow, IEEE

Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20740, USA


Today’s decreasing product development cycle time requires rapid and cost-effective reliability analysis and testing. Qualification is the process of demonstrating that a product is capable of meeting or exceeding specified requirements.Light-emitting diode (LED) qualification tests are often as long as 6,000 hours, but this length of time does not guarantee the typically required lifetime of 10 years or more. This paper presents a prognostics-based technique that reduces the LED qualification time. An anomaly detection technique called the similarity-based-metric test is developed to identify anomalies without utilizing historical libraries of healthy and unhealthy data. The similarity-based-metric test extracts features from the spectral power distributions using peak analysis, reduces the dimensionality of the features using principal component analysis, and partitions the data set of principal components into groups using a k-nearest neighbour (KNN)-kernel density-based clustering technique. A detection algorithm then evaluates the distances from the centroid of each cluster to each test point and detects anomalies when the distance is greater than the threshold. From this, the dominant degradation processes associated with the LED die and phosphors in the LED package can be identified. In our case study, anomalies were detected at less than 1, 200 hours using the similarity-based-metric test. Thus, our method could decrease the amount of LED qualification testing time by providing users with an earlier time to begin remaining useful life prediction without waiting 6,000 hours as required by industrial standards.

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