# COMMUNITY : FORUMS : BURNING QUESTIONS

## LED Resistors

I`ve been searching around everywhere about Resistors and how to use them, I understand that they resist power to the LED light t to a safe limit, but I need a noobs guide on how to use them, can someone help me?

guyfrom7up8 years ago
Well, to light up an LED search for LED calculator, if you actually want to know how to use them with a formula, here' the following info I typed in another form

Here's a run down on LEDs

Minimum voltage to light (voltage drop):
Red-1.7
Orange/Yellow - 2
Green - 2.1
White/Blue - 3

How to determine the resistor (formula):

Voltage input - Voltage drop X 50 = Resistance in ohms

(BTW the x 50 comes from 20mA LEDs take, 1/0.02 = 50, and it's easier to do that than a small divide)

Example, power source is a 9 volt lighting up one red LED
9-1.7 = 7.3
7.3 x 50 = 365
you need a 365 ohm resistor, give or take some, you don't have to be super exact with the resistor

Another example
source is a 12 volt wallwart
lighting up 3 white LEDs in series
12-3-3-3 = 3
3 x 50 = 150
you need one 150 ohm resistor in series with 3 white led's when the power source is 12 volts.
Alcreion (author)  guyfrom7up8 years ago
Very useful information, but how to i connect resistors too?
8 years ago
well, you just put the resistor in series if you have multiple LEDs in parallel, each set of parallel MUST have their own resistor. You can't just have one resistor driving a couple of LEDs in parralel