How to Wire LEDs - 101 - Single LED Example + Formulas

Posted on February 11, 2019 by LighthouseLEDs There have been 0 comments

We are going to show you several ways to wire LEDs.

This is a basic understanding of how to wire LEDs, however this article will allow you to wire LEDs in 99% of all scenarios.

The very basics of wiring an LED will involve your power supply (DC/Direct Current is best), a resistor(helps not "burn up" your LED) and an LED(s).

Things to ask yourself before starting.

  • What is the maximum voltage my power supply will provide?
  • How many LEDs do I want to wire?
  • What colors are the LEDs?

 

Single LED Wiring

Let's say you want to wire a single LED in a vehicle as some sort of indicator light. Most of us know that vehicle system is 12vDC, HOWEVER when charging it can definitely see higher voltages. We usually say that it shouldn't exceed 15v. That may be a tad high, but it is a safe number.

 

We have one RED 5mm Round Top LED that we want to wire up to the vehicle and have already found where we will take our power and ground from in the vehicle for the "12v" source. Looking at the technical specifications for this LED, we know it requires 1.9-2.1v @ 20mA in order to work at approximately it's peak light output. If we hook it directly up to the 12v power and ground then it will instantly burn out and be ruined forever.

 

This is where the simple electrical component, resistors, come in to play. They will allow you to use the LED on higher voltage without ruining them. There are plenty of LED calculators our there that will help you determine the appropriate resistor, but we can easily do some calculations by hand to show you a little of what's going on behind the scenes.

 

Formulas for LED Resistor Selection

V=IR (Voltage = Current x Resistance)
P=IV (Power = Current x Voltage)

 

Power is measured in Watts
Current is measured in Amp or milliamps (mA)
Resistance in measure in Ohms

 

Calculating Resistance Value 

Rearranging the first formula to solve for resistance we get the following:
R = V/I

 

If we solve for Resistance then we get something like this:
R = (15v - 2v) / .020A
The voltage value needs to be what is left over AFTER the LED's needs. In this case, our maximum voltage is 15v because it is from a vehicle. The LED requires 2v, so that will leave us with 13v in excess. The LED uses 20mA, which is the same as .020 Amps. The formula works when you use amps.

 

If we divide it out then we get R=650 Ohms
This is the resistance value and is very important. We want to choose a resistor with the resistance rating OR HIGHER.

 

 Calculating Power Rating for Resistor

The  next very important part to resistor selection is the power rating of the resistor. This is a rating that states how much power (in the form of heat) a resistor is able to dissipate. Typically the larger difference in voltage between the supply and required amount for the LEDs then the higher the power resistor that is needed. This can also be drastically changed by using higher power LEDs that use more current.

 

P = IV
P = .020A x 13v
Since this is being calculated for the resistor we have to say that the current going through the resistor is that of the LED (.020A) and the voltage is 13v.

 

Solving for P = 0.26 Watts

 

This is slightly more than 1/4 watt. These are all theoretical values that we have calculated, so real world can be a little different. In this case we would expect it to be a little less because the voltage likely won't be 15v and the LED will likely see just under 20mA at maximum operation of 15v.

 

How to Choose an Actual Resistor for your LED

Choosing the correct resistor. Since the power dissipation is close to 1/4 watt or over then we want to choose a 1/2 watt rated resistor. If we go and take a look at the 1/2 watt rated resistors, we can see that the closest value to 650 ohms AND higher is the 680 ohm 1/2 watt resistor.

 

That would be the best resistor selection for this scenario: 680 ohm 1/2 watt resistor. This will provide a very long life for your LED.

 

Some notes about adding a resistor to your LED

  • Resistors do not have polarity. You can put them on in either direction
  • It's easy enough to just put the resistor on the positive side of the LED (longer LED)
  • Soldering is always the best way of attaching the LED and the resistor.

This post was posted in General LED Information and was tagged with 12v, leds, how to, wire, car, volt, parallel, series, single