LED Anode vs Cathode: What You Need to Know

If you’ve just started researching into LED lights and diodes in general, you may be confused by some of the terminology used. That’s perfectly understandable as there are quite a few terms in this area that you may not have heard before. Rest assured that LED polarity, as well as the whole anode vs cathode question, is actually quite simple

What are LEDs?

The “LED” in LED lights stands for “Light-emitting diodes” – these are light bulbs that consist of multiple tiny diodes that have electrical currents running through them, causing them to emit light.

These light-emitting diodes are a variation of standard diodes which have applications in lots of other industries. The simplest description of a diode is “a two-terminal electronic component that conducts current primarily in one direction”. A light-emitting diode is simply a normal diode that uses the current passing through it to emit light.

What is LED polarity?

The term “LED polarity” relates to the question of which way the electrical current flows through the diode in? Because diodes are one-way currents it’s important to know from which side the current is getting in and from which it’s going out. The LED polarity identification is done through various identifications situated around the diode’s anodes and cathodes.

What are anodes and cathodes?

The anode and cathode are the two terminals on each diode where the electrical current flows through. The anode is the LED positive side (where the current enters the diode) and the cathode is the negative side (where the current leaves the diode).

Knowing which terminal is the anode and which is the cathode is important for LED polarity marking if you want to properly connect the diode to the LED bulb or another device.

How to differentiate between anodes and cathodes?

Now that we know that the anode is positive and the cathode is negative, we need to know which is which. Depending on the type and model of the diode, there can be various different identificators for knowing which side of the LED is positive and which is negative. Here are some things to look for:

  • Most diodes usually have a line drawn near the diode cathode pin which corresponds with the vertical line in the diode circuit symbol.
  • In LEDs, the LED anode-cathode differentiation is done via the length of each pin at the end of each diode – the longer pin is usually the anode and the shorter pin – the cathode.
  • If the pins have been trimmed and equal in length, look at the edges on the diode’s outer casing – one should be flat and in line with the diode and the other should be extending a bit. The pin near the flat edge should be the cathode.
  • If you’re still uncertain you can just use a multimeter to test which end of the diode is its anode and which – its cathode. Just turn the multimeter to its diode setting (it should be identified with a diode-shaped symbol) and touch each probe of the multimeter to the diode’s terminals. If the diode lights up then you’ve successfully matched the positive probe with the anode and the negative probe with the cathode. If not – switch them and try again.


Blogger, editor, developer who loves green living. Interested in photovoltaics and solar lighting. Reviewing solar products since 2013.

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