Light Emitting Diodes (LED)

Synopsis

Light emitting diodes may shift in color and degrade in the luminous flux output during operational life.  An excessive color shift or excessive degradation in the luminous flux output, usually to 70% of the initial luminous flux, constitutes the failure of the product.  In the current state of art a color shift of Δu’v’  less than 0.007 after 6,000 hours of operation is achievable.  Degradation in the luminous flux and the color shift is attributed to a number of factors including – exposure to high temperatures, change in the refractive index of the lens and encapsulant, discoloration of the reflector, corrosion and depolymerization. Research focus is on the development a life prediction model, early defect detection, lifetime prognostics and color shift prognostics

Representative Publications

1. Lall, P.,, H. Zhang and L. Davis, Color Shift Analysis and Modeling of High Power pc-LED under High Temperature and High Humidity Enviornment, in Proceedings of the 16th ITherm, Orlando, FL, pp. 1161-1177, May 30 – June 2, 2017.
2. Lall, P., Sakalaukus, P., Davis, L., Improvements to the IES TM-28-14 Lumen Maintenance Standard: A Generalized Acceleration Factor Approach for Solid-State Lighting, Proceedings of the 66th ECTC, Las Vegas, Nevada, pp. 1342- 1352, May 31- June 3, 2016.
3. Lall, P., Zhang, H., Davis, L., A Comparison of Temperature and Humidity Effects on Phosphor Converted LED Package and the Prediction of Remaining Useful Life with State Estimation, Proceedings of the ITHERM 2016, Las Vegas, Nevada, pp. 207- 217, May 31- June 3, 2016.
4. Lall, P., Sakalaukus, P., Davis, L., Reliability and Failure Modes of Solid-State Lighting Electrical Drivers Subjected to Accelerated Aging, IEEE Access Journal, Vol. 3, pp. 531-542, May 2015
5. Lall, P., Zhang, H., Assessment of Lumen Degradation and Remaining Life of Light-Emitting Diodes Using Physics-Based Indicators and Particle Filter, ASME Journal of Electronic Packaging, Volume 137, No. 2, doi: 10.1115/1.4028957, pp. 1-10, June 2015
6. Lall, P., Wei, J., Prediction of L70 Life and Assessment of Color Shift for Solid State Lighting Using Kalman Filter and Extended Kalman Filter Based Models, IEEE Transactions on Device and Materials Reliability, Volume. 15, No.1, doi 10.1109/TDMR.2014.2369859, pp. 1-15, March 2015.
7. Lall, P., and H. Zhang, L. Davis, Failure Mechanisms and Color Stability in Light-Emitting Diodes during Operations in High-Temperature Environments in Presence of Contamination, Proceedings of the 65^th ECTC, San Diego, CA, pp. 1624-1632, May 26-29, 2015
8. Lall, P., Sakalaukus, P., Davis, L., An Investigation of Catastrophic Failure in Solid-State Lamps Exposed to Harsh Environment Operational Conditions, Paper IPACKICNMM2015-48257; Session 1-5-1, ASME International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems (InterPACK), San Francisco, CA, pp. 1-7, July 6-9, 2015
9. Lall, P., Zhang, H., Davis, L., Discoloration and Failure Mechanism Analysis of High Power pc-LED Under Harsh Environment in Presence of Contamination, Paper IPACKICNMM2015-48724; Session 1-5-1, ASME International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems (InterPACK), San Francisco, CA, pp. 1-9, July 6-9, 2015
10. Lall, P., Wei, J., LED Chip Deformation Measurement During the Operation Using the X-ray CT Digital Volume Correlation, Paper IPACKICNMM2015-48785; Session 14-5-1, ASME International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems (InterPACK), San Francisco, CA, pp. 1-6, July 6-9, 2015