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LED Life Test Setup

LED Life Test Setup

Performance Characteristics of Light-Emitting Diodes (2002)

Light-emitting diodes (LEDs) have evolved from being a light source for indicator applications to a source for illumination applications. The traditional 5 mm and surface mount device (SMD) packages were developed specifically for indicator lighting applications. Recently, high-power LED packages have been designed specifically for general lighting applications. The performance characteristics of these different LED packages and different colored LEDs vary significantly. Having a better understanding of how these LEDs perform under various operating conditions can be beneficial. Therefore, the LRC conducted an experiment to quantify the light output change as a function of time for the different colored LEDs and different LED packages.

EXPERIMENT

An imaging type setup was used to monitor the relative light output change of the various LEDs. Groups of five 5 mm LEDs (red, green, blue, and white) and groups of five SMD LEDs (blue and white) were driven continuously at constant currents of 20, 30, 40, 50, and 60 mA. Their relative light outputs were monitored at regular intervals for 10,000 hours. The room temperature was maintained nominally around 25oC, and the relative humidity in the room remained below 30% throughout the experiment.

CONCLUSIONS

The light output degradation rates were different for the different colored LEDs, and their degradation rates increased when the drive current was increased. For white LEDs, the 5 mm and SMD packages had similar light output degradation rates and reached 50% of their initial value in less than 6000 hours. The newer high-power LEDs had very low light output degradation.

One significant problem noticed with the different types of white LED packages — 5 mm, SMD, and high-power — is that all of them had perceivable color differences between similar LEDs and also shifted in color with time.

Light Output
ACKNOWLEDGEMENTS

B/E Aerospace Inc. and the New York State Energy Research and Development Authority (NYSERDA) are thanked for their financial support.



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