Approximately 2% of all diodes are defective, so it is important to know how to check the LED for defectlessness. The 2835 LED has become the most widespread. It has a good light output combined with a large scattering angle, as well as compactness and reasonable price. It is used in flashlights, low-voltage lamps, car headlights, LED strips, household lighting fixtures. There are several types of 2835 LED. All of them differ in voltage drop, luminous flux, current strength.

How to test an LED with a multimeter

An LED is a semiconductor device with two leading electrical parameters:

  • working current;
  • voltage drop.

There are several ways to check the health of the diode.

Checking with a multimeter

A multimeter is a device that measures the main parameters of an electrical device. To check the LED for operability, you need a multimeter with a “continuity” mode – checking diodes. See wholesale LED strip from the manufacturer.

Checking the LED with a multimeter:

  1. Put the probes into the holes on the tester: black – COM, red – V.
  2. Set the dialing mode.
  3. Connect the probes to the LED: red probe – to the anode (+), black – to the cathode (-). The LED will not break if the probes are not connected correctly. Just the multimeter readings will remain unchanged. When the probes are connected correctly, the working LED will shine.

The current strength (power supply) in the “ringing” of the multimeter is not enough for the diode to glow at full power. Therefore, you can see the glow in the twilight. If it is impossible to turn off the light, then the tester readings will indicate the health of the LED – they differ from 1.

Check by tester

The second way, checking the performance of the LED with a tester, is to use the function of monitoring the health of transistors. Under the scoreboard there is a round connector (usually blue) with holes in a circle. To the right above this connector is NPN, to the left is PNP.

LED tester

To make sure the LED is working, you will need to insert its legs into these holes:

  • PNP: long leg in “E”, short – in “C”
  • NPN: long – in “C”, short – in “E”.

The legs have different lengths only for diodes with low power. The longer leg of the LED is the anode (+) terminal, the short leg is the cathode (-).


For powerful LEDs, “+” and “-” are indicated on the outputs. For SMD 2835, SMD 5730 “-” is indicated by a cut corner of the case.

The ringing of high power LEDs operating at currents of hundreds and thousands of mA is usually accompanied by a glow and shows that the elements are operational. But when turned on to the operating current, they seem to shine “at half strength”. This indicates damage to the crystal, which is difficult to change (for example, in a spotlight) and therefore a check should be made in advance.

Before checking, it is recommended to carefully inspect the LED. If this is a large yellow square, then it is impossible to find out its performance with a multimeter, since the voltage of such a light emitting diode exceeds 20 volts.

A spotlight of several small smds is checked by a tester. You need to disassemble the spotlight and find the diode board.


  1. Set the toggle switch of the tester to test LED diodes.
  2. Attach the probes to the LED. It is important that the red wire is powered from “+”, black – from “-“. If the connection is correct, the diode will light up.

To check the infrared LED, you need to insert it into the holes of the transistor connector and look through the mobile phone’s video camera. Human vision does not detect infrared rays. A working LED looks like a luminous spot with blurry contours on the phone screen.

Checking the LED at home

At home, you can test the LED by connecting it to a power source. For example, to charge a mobile phone or a flashlight. The tester can be made from an old phone charger or other unnecessary electrical appliance.


  1. Cut off the connector at the end of the power cord and strip the wires.
  2. The red wire is connected to the “+”, the black wire is connected to the “-“. If the power supply is 1.5 volts or more, then the diode will start to glow.

The LED strip consists of several LED elements, they are assembled 3 pieces per segment. This allows you to divide the tape, and its performance will not change.


  1. A working tape will light up after the electric current is applied to the contacts completely.
  2. If a small segment glows, then the conductive wire is not in order. It needs to be checked by a tester.
  3. LEDs are faulty when 3 pieces are not lit in a row.

Is it possible to check with a battery

You can check the diode without a tester using a Krona battery (9 volts) or several finger-type batteries connected to each other. Checking super-bright (yellow, white, blue) diodes is a simple procedure. It is enough to connect more than 3 volts – 4.2 volts to the terminals of such an element.

A 3 volt battery (or 2 pieces of 1.5 volts each) can be used as power when checking performance. White and blue LEDs are tested without using a resistor (it limits the current). For yellow and red, a 60-70 ohm resistor is needed. It is best to use a discharged round coin cell battery. For example, from electronic floor scales.

Testing the LED with a battery


  1. Attach 1 needle from a disposable syringe to the battery with tape on one and the other flat side.
  2. Check diode performance.

How to check without soldering

Most often, a light emitting diode is part of the LED system, and without desoldering, putting it into the connector will not work. It will also not work to check the serviceability using probes, because they cannot be plugged into the connector. You can explore the LEDs without soldering by making a simple device from an adapter with probes. Ordinary paper clips are perfect as an adapter (the holes in the NPN and PNP connector of the multimeter are small).

how to check battery led

How to ring the LED:

  1. Solder straightened paper clip adapters to tester probes. For more reliable insulation of cables with staples, you need to place a textolite between them and rewind the resulting device with electrical tape.
  2. Insert paper clip adapters into the holes of the NPN or PNP connector, and attach the probes to the LED contacts. At the same time, there is no need to unsolder it from the system.

LED test

Checking the diode will not cause much difficulty. Absolutely anyone can handle it. For this, it is not necessary to have knowledge from the field of electrical appliances. Or understand what a “volt” is. It is enough to want to check the performance of light emitting diodes yourself. Rgb LED strip.

LEDs are more economical and more reliable than ordinary light bulbs, but they can also be defective or simply fail. There are several ways to test an LED. For example, with a multimeter or using ordinary batteries as power in combination with improvised means (paper clips, needles from a syringe). The simplest, most accurate and reliable check is by a tester.