Test LED emit light or not using Multimeter

Test your LED using Digital Multimeter by simply connecting lead to cathode-anode ends of LED. LED is a type of diode that emits light when external voltage is applied.

Steps to Test LED:

Connect the black lead to the COM terminal on the multimeter.
Connect the red lead to the Ohm terminal, unless your particular model differs.
Turn the dial to the diode symbol on the multimeter. This allows for electric current to travel in one direction (the arrow) and not the other.
Choose a regular red LED.
Connect the black probe to the cathode end of the LED, which usually is the shorter end and/or cut flat at its bottom. Connect the red probe to the anode end of the LED.
You will find that LED will light up, showing it is correct to use in your project.
LED will light due to the battery power of multimeter and completing the connection.

LED Forward Voltage Drop The value displayed on your multimeter is called the forward voltage drop. This indicates the quantity of voltage used up by the LED, or dropped, when current is traveling in the appropriate direction, forward. This kind of data is extremely useful when it comes to building your own robot or designing your circuit board. You will definitely need to keep track of the total voltage used by your robot, whether it is from a LED or some other component, in order to choose a battery strong enough to power it. Therefore, it is equally important for you to purchase the LEDs that your battery can sustain. Usually, you should not purchase an LED with a forward voltage exceeding 4V, because most robotic circuits can not function at such voltages.

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