Dave's Circuit - White LED Lifetime Tests

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White LED Lifetime Tests
By: Dave Johnson -- March 1, 2010

Problem: All white LEDs fade over time. I find that some LEDs fade in intensity very rapidly while others fade more slowly but every one I have tested would be worthless in a few months to a year.

Solution: To speed up the testing process I have modified my constant current LED driver circuit as shown below.

White LED Lifetime Test Circuit

This new circuit can test 4 LEDs at the same time. I have a separate photodiode monitoring the light output from each device. I have also mounted a battery operated hour meter to the circuit. This should make it easier to plot light output Vs time curves for several parts.

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DC Magazine, Issue 7, Page 4: White LED Lifetime Tests