Cree describes the testing and characterizing of LED lumen maintenance as “an evolving science based on decades of work from the component semiconductor industry.” The company has fully characterized the XLamp XR-E LED lamp and has developed an accurate predictive model for its long-term lumen maintenance. The key inputs are:
• LED junction temperature (TJ), calculated from the solder point temperature (TSP)
• Forward drive current (IF)
• Air temperature around the lamp (TAIR)
From these inputs, L70 for the LED lamp can be predicted with confidence. Figure 1 shows the predicted L70 lifetime for devices driven at 350 mA, and clearly demonstrates the effect of TAIR. Different curves have been measured for different drive currents.
This article was published in the Sept/Oct 2009 issue of LEDs Magazine. To read the full version of this article, please visit our magazine page, where you can download FREE electronic PDF versions of all issues of LEDs Magazine.
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