Memcon Tech Tip: Testing LEDs

Some LEDs initially do not illuminate during testing, but when they are re-tested on the same set-up after attempting to troubleshoot the problem they work fine

The final test device is testing the LED at low current levels, LEDs are non-ohmic devices, initially have very high and inconsistent resistances at low level current levels, so some of the LEDs may be seen as open circuits, while some will pass.

When a separate power source, or even a good multi-meter is used to illuminate the LED during troubleshooting, the LED can be "burned in". This generally reduces the resistance of the LED and makes the resistance from LED to LED more consistent at low current levels used by the final tester for testing, so the LED illuminates and passes when re-tested.