Identifying the Positive (+) and Negative (-) Sides
2. The Clues are in the Leads (and Sometimes the Packaging!)
Okay, detective time! Let’s examine those LED leads closely. The most common way to identify polarity is by looking at the length of the leads. The longer lead is generally the positive (+) side, also known as the anode. The shorter lead is the negative (-) side, or the cathode. Easy peasy, right?
But wait, there’s more! Sometimes, especially with older or less expensive LEDs, the leads might have been trimmed, making it hard to tell which one was originally longer. Don’t panic! Another clue is the shape inside the LED. Look closely at the internal structure. You’ll often see a tiny, flat spot on one side. This flat spot usually indicates the negative (-) side.
And if you’re really lucky, the packaging might have markings! Many manufacturers will clearly indicate the positive and negative sides on the LED’s packaging or datasheet. This is the easiest method, of course, but don’t always rely on it; packaging can get lost or damaged.
Finally, if you’re using a multimeter, you can use the diode test function to identify the polarity. Connect the red probe (positive) to one lead and the black probe (negative) to the other. If the LED lights up dimly, you’ve got the polarity correct. If nothing happens, reverse the probes. If it still doesn’t light up, the LED might be faulty, or you’ve stumbled upon some seriously weird wiring. Either way, move on to another LED and try again!