How to Identify Diodes: Three Main Techniques to Identify Diodes Polarity

Welcome to our elaborate discussion on how to identify diodes

Notably, we have numerous regular diodes, each suited to a specific purpose in an electric circuit. Does that mean that each of them features a unique diode symbol? 

Hence, join us today to learn more about these semiconductor devices as we explore diodes. We’ll cover all you need to know about identifying diodes and how to tell their values from their color codes. 

Let’s get started. 

What Is a Diode?

All normal diodes are electronic components that primarily feature two terminals through which electric current flows from one end to the other. 

Its role is to ensure unidirectional current flow as guided by the resistance setting at either of the terminals. 

The resistance reading is relatively high on one end and low on the other. It is the underlying principle behind the unilateral current flow. 

You can identify a normal diode on a circuit via the diode symbol below. 

A Diode Symbol 

A Diode Symbol 

Note that the diode features an anode and cathode. Also noteworthy is that one end of the diode has an arrowhead, which indicates the direction of conventional current flow during forward bias. 

Notably, when the cathode voltage is less positive than the anode voltage, this is a forward bias mode and vice versa. 

Diode Materials 

The primary makeup material of any diode is either a germanium or silicon. 

Understanding the two bias modes is also essential when dealing with any type, whether Germanum or a silicon diode. 

Types of Diodes

We have several kinds of diodes, including the following: 

  • Photodiode- A photocell is a form of photodiode
  • Avalanche diode
  • Normal PN junction diode
  • Schottky diode
  • Laser diode
  • Light Emitting Diode such as a Green Light-Emitting Diode
  • Zener Diode
  • Silicon Controlled Rectifier (SCR) Diode
  • TRIAC Diode
  • Junction Diode
  • Tunnel Diode
  • Varactor Diode
  • Diac Diode

As we mentioned earlier, each of the diodes has a unique representation, as we have captured in the diagram below. 

Note that for each type, the underlying symbol of an arrowhead remains primarily to indicate the direction of the current flow. 

Diode Cathode vs Anode: Diode Anode Cathode Identification

Let’s examine the three main techniques to determine a diode from other active components. We’ll also cover how to tell its polarity. 

Visual Inspection

It is the simplest method and typically involves checking if the component features a grey cylindrical line on its circumference. 

This line is usually towards one end of the element. To use the technique, check out this line. 

Note that the side towards which you’ll find the line is the cathode output terminal; hence it is negative. Conversely, the other end is positive. 

A Diode. 

A Diode. 

While this is a straightforward technique to check out polarity, it may not always work as not all diodes have the feature. An example of an unmarked diode is the LED. How do you determine its polarity?

LED Polarity Identification

(Blue). Light-Emitting Diode Physic

(Blue). Light-Emitting Diode Physic

Here’s a rule of thumb when dealing with the type of diode called LED: Always connect it in a forward bias mode; otherwise, it will not light up. 

This condition means you must know the polarities of the LED (Light-Emitting Diode) terminals. 

It is easy to decipher polarity primarily by checking out the length of the individual legs/terminals.

 Invariably, the shorter leg represents the cathode, while the other is the anode. 

But again, you could have the dilemma of an LED with the same-sized legs. So how do you determine polarity in such a case? 

There’s still a way to tell the polarity. Check out the discontinuous side inside the LED (Light-Emitting Diode) casing. The part with the disjoint is the anode. 

Using a Component Tester

The second most effective method to know your ordinary diode’s polarity is to use an M328 Transistor Tester.

 It is the simplest technique to check for polarity as it involves your diode on the tester’s terminals and reading the polarities from its screen. 

This technique can also tell if you’re dealing with a dead diode. If it’s not working, it will not give a reading. 

Finally, it can help you determine the various output terminals of an unmarked diode. 

Using a Multimeter

A Multimeter. 

A Multimeter. 

Finally, you can use a multimeter in voltage mode to ascertain the cathode and anode terminals of the diode. 

It’s also straightforward. Simply place its probes on either end of the diode and check out for the reading. 

If there’s no current flow, you have the polarities wrong. So interchange them, and you will obtain a reading. 

The multimeter probes will now guide you on the respective polarities of the diode. 

In principle, the red one connects to the cathode, so this tells you that it should go to the diode’s negative terminal. Hence, the other side is the anode. 

How Do I Identify a Diode’s Value?

A Diode. 

A Diode. 

First, identify your diode’s cathode by checking the side with a colored band.

 This is the cathode, and when checking out the diode’s value, this side should be on the left-hand side. 

Looking keenly at the diode, you’ll notice several multicolored strips on the cathode end. 

Identify the colors from left to right and use the color code table below to identify the diode’s value. 

  • Black – 0 
  • Brown – 1 
  • Red – 2 
  • Orange – 3 
  • Yellow – 4 
  • Green – 5 
  • Blue – 6 
  • Violet – 7 
  • Gray – 8 
  • White – 9

Usually, we use the first three strips as read from left to right to tell a Diode’s value. 

Also noteworthy, in scenarios where the diode has a maximum of three stripes, the last strip indicates the no. of zeros in the diode value. 

For instance, Take a Diode that is RED, RED, BROWN. The value of such a diode is 220 Ohms. 

You can also tell the tolerance value of the diode from its accuracy tolerance band, which is usually the fourth one. 

If its color is Gold, the diode’s tolerance is positive or negative five percent. 

But if your diode’s fourth band is Silver, it can tolerate up to 10% of the total diode value. 


A diode switch makes it possible to have current moving unilaterally in any electronic circuit. 

So it is a critical component as it dictates the direction of flow of the valence electrons. 

Also, you can quickly tell out the anode and cathode given any type of diode using the three methods outlined above. 

For your PCB design project, we now challenge you to take any kind of diode and try to decipher its value. Adios and sucess in your project.