Resistor information


What is a Resistor?

A resistor is a device that limits current flow and provides a voltage drop in electrical circuits.

Resistor Color Codes: Because carbon resistors are very small, they are color-coded to identify their resistance value in Ohms (Ω). This coding is standard.

Use the following Resistor Color Code Chart to understand how to use code system. In the illustration there are three resistors with 4, 5, and 6 colored bands. Each band is associated with a numerical value.


Read the resistor from left to right. The right end usually has a single gold or silver band.

1.       Determine the digits. There will be two or three digits, depending on the resistor.
2.       Determine the multiplier. This will be rightmost band on the left end of the resistor (third or fourth band).
3.       Multiply the two- or three-digit number by the multiplier. This is the Ohm value.
4.       Determine the tolerance. This will be the first (leftmost) band on the right end of the resistor.
5.       Determine the temperature coefficient (if applicable). If there are two bands on the right end of the resistor, this is the rightmost band.

What Resistor Should I Use with My LEDs?

In order to determine this, you must first know the following about the LED and the voltage source:

·         The voltage of the power source

o   Supply Voltage- this is how much power you are putting into the circuit

·         The number of LEDs being wired
·         The wiring method being used (click here)

o   Single- for one LED

o   Series- for multiple LEDs (end-to-end)

o   Parallel- for multiple LEDs (side-by-side)

·         The voltage drop of the system

o   Working Voltage- LED voltage in Volts (V), found in the LED datasheet

·         The recommended milliamps (mA)

o   Working Current- LED current in Amps (mA) or (A), found in the LED datasheet

With this information, a resistor calculator can be used to determine what type of resistor you will need. Please call our tech support if you need assistance. 


Parallel Method: Devices placed in parallel will have the same voltage (V) and different current (mA).
When wiring in parallel you always need a resistor!.
A parallel circuit allows you freedom when choosing how many LEDs you would like to wire. This kind of circuit works great if you have a small voltage source and need multiple LEDs.
When wiring in parallel, you wire the + legs together and the - legs together.
Single Method:
  Resistance = (Supply Voltage - Working Voltage) / (Working Current / 1000)
So, If we want to connect a 5mm Blue Ultra Bright LED (3.1V, 20mA) to a 12V Power Supply, our formula becomes:
(12 -  3.1) / (20 / 1000): 445ohms
Other example:
We have a 5mm Red Ultra Bright LED (2.1V, 20mA) to a 12V Power Supply, our formula becomes:
(12 -  2.1) / (20 / 1000): 495ohms.
If you are using a web calculator you will get 560ohms with this formula, Why?? That is because it is hard to buy a 495ohms resistor. In this case, you need to use the nearest one you can easily find.
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