A Digital Multimeter (DMM) with a “Diode Test” function can help to easily test LEDs. Before testing whether the LED works normally, please pay attention to the following.
1. Check the test curent and forward voltage
It is necessary to know the test current and forward voltage of the LED being tested, as specified in a datasheet. For example, Everlight’s HLMP-K150 LED can test under 1mA test current and 1.6V forward voltage.
2. Ensure enough output voltage and testing current for testing LED
Most modern DMMs are capable of supplying enough voltage to perform most typical LED tests. But please note that different DMMs can provide different values of test current and output voltage in Diode Test function. If insufficient voltage and current exist, the meter cannot confirm whether the LED is working or display its brightness.
For example, B&K Precision 2703C DMM can supply 1mA test current approximately and 3.0V typical output voltage in “Diode Test” function. If testing a high brightness LED, such as Luminus, SSR-90-W65S-R11-N3102 which requires 3.15A test current, your 2703C DMM can’t help with its Diode Test Function. So in this case, an external power supply and a resistor circuit need to be set to ensure that the test current and forward voltage meet the LED testing requirement.