Light Emitting Diodes – Indicator LEDs

Light emitting diodes (LEDs) are a type of diode that is made to light up while forward biased and passing current. Indicator LEDs will be the focus of this page. They are usually 3 – 5mm round through hole components that commonly come in electronics kits.

Basic indicator LED properties

Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom



Nice looking LED kit. Good to have a lot of LEDs because it’s relatively easy to damage them or to want to use a lot of them in various projects.

  • Series resistor must be used to protect the LED. For most LEDs, the resistor should limit current to no more than 20mA of current for whatever voltage is used.  Resistor limiting current – Ohms law
  • Anode usually has a longer lead than the Cathode as long as they haven’t been trimmed. Cathode often has a flat edge.
  • Many multimeters can test diodes/LEDs. LED lights up when the red probe is touching the anode and the black probe is touching the cathode. LED does not light up when red probe is connected to Cathode and black probe is connected to the Anode. Meter will likely tell you the forward voltage as well.
  • Forward biased (FB): Anode more positive than Cathode. LED lights up once forward voltage is reached. Exact voltage is slightly variable. Typically about 1.8V for red LEDs, and about 2.8V for green or blue LEDs.
  • Reverse biased (RB): Cathode more positive than Anode. Best to keep at low voltages. I avoid going above 9V RB

Simple LED circuit diagram

Basic electronics LED circuit expectations using a 9V 500mAh battery 470 ohm or 1K resistor diagram by electronzap electronzapdotcom
Basic electronics LED circuit expectations using a 9V 500mAh battery 470 ohm or 1K resistor diagram by electronzap electronzapdotcom
9V battery with snap wires to power current limiting resistor with LED circuit on breadbard diagram by electronzap electronzapdotcom
9V battery with snap wires to power current limiting resistor with LED circuit on breadbard diagram by electronzap electronzapdotcom
Related topics:

Other basic electronics topics that you should know before moving on to more advanced topics.

Good upcoming topics:

More advanced topics for after you have the basics down.

Circuits covered more quickly series:


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