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What is the best ohm resistor for LEDs? Answered

What is the best ohm resistor to use with a standard led to ensure that it won't burn out? Is it 330? Thanks!

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deeppu

5 years ago

15 ohm resistor is best for white leds

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deeppu

5 years ago

15 ohm resistor is best for white leds

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Axphey

6 years ago

Something in kilo ohms recommded best

if using 12v get a pack of 560 Ohm Works A Treat 

   In               Valu              Out
12V --------( 560 )-------- 2.5V

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dan

9 years ago

Actually, there is a best ohm resistor for use with all LEDs. This resistor was developed in 2005 by a good friend of mine at MIT. It was amazing! so convenient we could just use it on all the LEDs for perfect regulation. Problem was that it made things too easy. All the big lighting players like Phillips, GE, etc heard about it from some scientific reports and got really worried it would undercut their entire LED lighting business. Even scarier for them the possibility of further development of the resistor into a CFL suitable value. My friend was not doing so well at the time so GE was able to buy all the concepts and patents off him for under $1mil. Then they buried all of it in the vault. They are probably making that much in a day by making sure nobody knows about the perfect ohm resistor. sad but true.

It will vary depending on the LED and supply.
To work it out you need to know the 'forward bias voltage' and to 'operating current' both of these are listed on the datasheet that comes with the LED (if you are getting expensive ones) if you are getting the el cheapos then 2.5V and 20mA is a good starting place.

To work out your resistor you first take your supply voltage (for example 9V) and from that subtract the FWD Bias Voltage of the LED (in this case 2.5V)
so 9V - 2.5V leaves you guessed it 6.5V.
Now we know how much voltage we have to drop across our resistor. To work out how much resistance is needed we use Ohm's Law Voltage = Current * Resistance. Rearranged to find Resistance R = V / I
Therefore R = 6.5V / 20mA = 325Ohms
It doesn't matter if you can't get a resistor that is exactly that resistance, just get the closest one

Thats it, your done! go forth and light the world!

I like 100 Ohms if its a 9v battery or under, otherwise use like a 220 or 1K.

Generally speaking for most 5-12v applications anywhere from 220ohm-1Kohm is do-able. Depending on how bright you want it, how long you want the LED's to last and the specs on the LED's themselves. You might want to check the spec sheet for the LED's you are using and the rest of the circuit and run some numbers. If you want to do a quick test and play it safe without the math, add in a 200-220ohm resistor (as a safe base line) and a 1K pot in series, dial the pot to 1K and see how bright it is (it'll probably be fairly dim). Then start taking it down. Once you find the brightness you like, measure the pot and that is the value you need if you want to take the pot out and use a straight resistor. Let the lights and smiles begin :-)

330 is good for running off a 9v battery, goves around 27mA of current.