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Why is my Flexible LED Strip Light so Dim at One End?

Whenever a current is flowing, the current will meet some resistance or something will impede its flow, the amount of voltage loss through the entirety of a circuit, or even a part is voltage drop. In low voltage lighting systems such as flexible LED strip lights, voltage drops occur because the input voltage from the power supply gradually decreases over the length of the strip.

The longer the flexible led strip light tape, the more resistance the current has to overcome, hence it loses voltage along the way. The result is dimming lights the further down the LED strip you get because the light emitting diodes (SMD chips) at the end of the strip are less bright than those at the start, which is closest to the power supply. This condition causes the load to work harder with less voltage pushing the current.

If the flexible LED strip light runs off a 12-volt power supply, then you have 12 volts going into the strip light system at the start but the other end will not have 12 volts due to the voltage drop. This can be prevented with some simple rules that are outlined below.

Voltage drop is a function of wire length, wire thickness, and the total watts of power used by the flexible LED strip lights. A reduction of brightness and color accuracy in longer flexible LED strip lights is due to excessive voltage drop. The excessive voltage drop may result in unsatisfactory operation of, and damage to, electrical outlets and the flexible LED strip tape lights. The distance from the power source to the desired end distance of the flexible LED strip tape is called a run. Shorter and/or thicker wires will raise the brightness and color consistency to the strip lights’ full potential.

We at Fero LED Lighting can help you choose the right power supply, gauge of wire, and distance of wire to match the right length of flexible LED strip lights, so you experience minimal voltage drop. If the run is too long and you experience voltage drop, we will help you find solutions to overcome the problem.
voltage drop
One solution to a voltage drop issue is to run the LED strip lights in parallel. As pictured here, there are three parallel runs from one power supply as opposed to one power supply sourcing the full strip of lights. Ideally, you want the shortest length of wire from the power supply to the flexible LED strip lights. On the second and third run however, this is not possible, and on the third one we add a thicker gauge wire, which allows for more current to travel through the wire to the because of the larger surface area of wire.
A multimeter also called a multitester can be used to measure the voltage at the end of the run. The acceptable voltage drop for a flexible LED light system should not exceed %3 or be lower than .36 volts from a 12 volt input power supply.

12 volts x 3% = 0.36 volts.

At Fero LED Lighting, we will show you how to do this in an upcoming video.

Basic voltage drop law is Vdrop = IR

I: the current through the object, measured in amperes

R: the resistance of the wires, measured in ohms

When calculating voltage drop, keep these things in mind:

  • Total wattage draw of your flexible led light system- This is done by multiplying the wattage of your flexible LED strip light by the distance of your run. This will be either in meters or feet/inches depending on the information you are given about your flexible LED strip lights. Ex: If your 5050 60 LED/M strip lights are 14.4 watts per meter and the length of the strip light is 2.5 meters, multiplying 14.4 by 2.5 will give you the total wattage draw.
  • Length of the wire starting from the power supply to the front of the flexible led strip light.
  • Thickness of the wire you are using in your flexible led light system; the thicker the wire the smaller the number. This is known as wire gauge (AWG). This table shows the appropriate wire gauge to use depending on how far away the flexible LED strip light is from the power supply:


  • Wattage and amperage of direct current (DC) power supply.
  • Load current- In DC system there is no power factor, so we can find the current easily. Power=voltage x current       current(I)=power/voltage

 Click here for a voltage drop calculator.

Give us a call or e-mail our team at Fero LED Lighting, we would be happy to calculate how much strip lighting you can use before experiencing noticeable voltage drop. We can also show you how to set up the exact system you want for your flexible LED strip light project.

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