LEDs for Beginners


Step 7: Wiring up multiple LEDs in series

Now that I knew how to wire one LED with various combinations of LED voltages and power supplies, it was time to explore how to light up multiple LEDs. When it comes to wiring more than one LED to a power supply there are two options. The first option is to wire them in series and the second is to wire them in parallel.

To see an in depth explanation about the difference between series and parallel check out this page. I'm going to cover wiring LEDs in series first.

LEDs wired in series are connected end to end (the negative electrode of the first LED connects to the positive electrode of the second LED and the negative electrode of the second LED connects to the positive electrode of the third LED and so on and so on...). The main advantage of wiring things in series is that it distributes the total voltage of the power source between all of the LEDs. What that means is that if I had a 12V car battery, I could power 4, 3V LEDs (attaching a resistor to each of them). Hypothetically this could also work to power 12, 1V LEDs; 6, 2V LEDs; or even 1 12V LED if such a thing existed.

Ok, let's try wiring 2, 2.6V LEDs in series to the 9V power supply and run through the math.

R = (9V - 5.2V) / .02A
R = 190 Ohms
Next higher resistance value - 200 Ohms

Now the variety package of resistors didn't come with a 190 or 200 Ohm resistor, but it did come with other resistors which I could use to make a 200 Ohm resistor. Just like LEDs, resistors can be wired together in either series or parallel (see next step for an explanation on wiring things together in parallel).

When same value resistors are wired together in series you add their resistance. When same value resistors are wired together in parallel you divide the value of the resistor by the number of resistors wired together.

So, in the most simplified sense, two 100 Ohm resistors wired together in series will equal 1 200 Ohm resistor (100 + 100 = 200). Two 100 Ohm resistors wired together in parallel will equal one 50 Ohm resistor (100 / 2 = 50).

Unfortunately, I learned this key point after I wired my resistors together for the experiment. I had originally wanted to wire two 100 Ohm resistors together to equal the 200 Ohms of resistance I needed to protect my LEDs. Instead of wiring them in series, as it should have been, I wired my resistors in parallel (did I mention I am beginner with resistors?) So my resistors were only providing 50 Ohms of resistance - which apparently worked out OK on my LEDs in the short duration of the experiment. Having too much power getting to the LEDs would probably burn them out in the long term. (Thanks beanwaur and shark500 for pointing this out.)

I took my resistors and placed them in front of the positive lead of the first LED that was wired in series and hooked them up to the battery and once again, there was LED light!

With three different combinations of LEDs and battery power supplies and no puffs of plastic smoke yet things were looking good - aside from my little confusion between wiring resistors in series and in parallel.
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sushil0101 month ago

actually i already got 5 led(white) in series with 4.5 power supply..and there is one resistor well i dont care about that resistor. Now the main problem is supplying 4.5v to it is really difficult for me i need to buy batteries time n again,instead of that 4.5v i would like to replace with 12 volt(lead acid)battery just to supply power,for that what resistor do i need to replace with?please help me.

djmaxpaul3 months ago

I dont see why ppl complain about Series LEDs. I was 12 years old when I took apart Boom Box I had. I made about 9 holes in plastic with solder gun. Connected LEDs in Series. Plus LED Solder to Plus on speaker and last LED Cathode to Mines to Speaker. More volume more LEDs flashing showing how music is loud and worked as UV Meter. Not that big deal with Series LEDs. I didnt even used Resistors. Looked cool.

jdeth9 months ago
Well, this should say how to get lucky because you're using small power supplies and incorrect math to calculate current and voltage division.
Throw a meter on that circuit.
Your LED's are seeing about 45% of the voltage each, the resistor less than 10%.
The theory of operation for semiconductors is based on charge carrier theory.

I'm glad I stopped relying on internet "experts" to help out us beginners and finally went to college to become an electronic engineer a few years ago.

This is very rudimentary and bad science folks!
bradix14 jdeth6 months ago
jdeth, will you please clarify what the good science is and what we beginners should know differently than presented above before we go use this to do projects?
killrsheep7 years ago
Am i the only Electronic-Loving guy whou wonders WHY? Why god Why! why would you wire Leds in series?! LOL, but seriopusly, i just want to recommend to those who want to build Led projects to try and use paralell everytime, if for any reason something gets messed up the whole set wont light, if a Led gets shorted you will get a higher current than the one you calculated, Paralell sets are independent from each other, have a nice day, i didnt mean to sound like a "know it all" its just that electronics is the one subject im not faling this semester, thats why i love em
Can there a difference in the brightness if you use series ? say R= (6v-8.0)/.02mA
I am such a beginner!
because if you want to power 4 leds, why waste a resistor if you're using a 12 volt input and your leds take 3 volts?
wow, that comment is really old XD Now that i see the instructable again, its actually pretty well written and it does involve ohms law to make everything safe and functional, so yeah it does get a 5/5 however if you have 4 led that consume exactly 3 volts each (wich they dont) and you hook it up to exactly 12 V (wich is hard yet not impossible to achieve with the proper circuit) and we hook it up to a mm lets say car battery... im sure your LED's will light pretty bright for an instant and then die, im not encouraging anyone to do it, but if you do maybe some heat resistant gloves are a good idea. small batteries usually cant supply enough current to destroy LED's thats the reason why led throwies etc work without the resistor
ahwang3 years ago
I have a question but btw, you have an awesome website for ppl like me who's interested in learning to light up some LEDs!!!

Forward voltage: 3.0-3.2
Current: 20ma
Battery: 6V

1. Following your instruction, I first tested my 2 of my LED, in a series without any resistors to my 6V and baam! it lit up! thanks!
but after about 20 secs, the LEDs started to get hot. Is that normal? I don't think I'd need any resistors or I wouldn't even know how since I would get 0 ohm resistor value

2. My project is to light up 8 LEDs. 4 pararell LED each side, then 2 of 4 pararell LEDs in series. so like. (1+1+1+1) + (1+1+1+1).
so I'm thinking (3V, .08ohm) + (3V, .08ohm) so it would be 6V with .08ohm right?
then it would require no resistor since 6v-6v=0 right?
Or would that get too hot and require resistors?

any help is appreciated!!!
cellis6 ahwang2 years ago
LEDs power is based on Amperage not Voltage, that's why they are getting hot. Think of them like a resistor, when you put 2 resistors in series, you drop voltage each resistor but Amperage never changes.

So if your LED requires Forward Voltage of 3.0-3.2Vf, and 20mA, and you want to run it off 6V. If you were just trying to power one LED it would be (6V-3.2V)/.02mA. Meaning you'd need a 140 ohm resistor before attaching the LED to power.

As far as hooking them up in series/parallel, you should be able to do it with one resistor at the beginning of each series of 4 of 140 ohms. Which would make each series 20mA and 3.2 Volts after the resistor. Hope this helps.
jconner33 years ago
ok im trying to light up 12 white leds 3.3 volts what battery and resistor shoult i use
dkcmo3 years ago
I have a question i am going to hook up 36 led for lighting not sure what is the best way to connect them is it parallel or series what is the advantage from one to the other ?
m1445783 years ago
Can someone help me out?

I have two 5 Volt LEDs from radio shack. What would be the best way to hook them up and with what ohm of resistor?

gfear4 years ago
Hi - I've been interested to read all of these comments regarding LEDs and hope that someone here may be able to help. I have 40 x 5mm White Leds. I wish to use all 40 lit at the smae time and they were supplied with 40 x 0.25 Watt 68 ohm resistor. It makes no difference to me if they are wired in parallel or in series and I would appreciate your advice on the best way. Can I use just one resistor for the whole circuit or will I have to use more resistors or even all 40 of them? The only other information I have about these is as follows: Specification : - Emitting Color: White - Lens Type: Water clear - Material: InGaN - Luminous Intensity: 27,000+ mcd - Viewing Angle: 20 ± 5 Degree - Reverse Voltage: 5.0 V - DC Forward Voltage: Typical: 3.2 V Max: 3.4 V - DC Forward Current: 25mA Can anyone help me - I would really appreciate it - not very strong on electronics! Regards Gary
do we really need he reisistor
tvilot5 years ago
"or even 1 12V LED if such a thing existed."

Actually ... such a thing now does exist!!!

I need help : ( How is he figuring out the resistor amount and stuff. I understand everything but the resistors and the calculating. any help is much apprieciated. Thank you : )
grizzly g5 years ago
wait how do you accidentally put the resistor in a parallel? could you show one thats in a series?
So in theory if a car has a 12v battery i can use 12 led with out resistors? Now since a cars battery fluctuates sometimes going from 10v to 14v do you recomend a resistor? if so what size or color scheme? im basiicaly trying to change the lights in my dash, i think theres a instructable here about just that but it doent really go into detail about resitors.
in theory, actually in theory you would get an infinite amount of current that way so, no, not with a car battery, first check how much voltage does your LED's actually need, 1V seems too little 4 me, i havent seen that kind of LED yet

i changed the lights on my dash using LED's , if you are going to use series calculate your circuit for 14V so your resistance should be R=(14V - (Nleds*Vleds))/0.02Amp where Nleds is the number of leds you are using and Vleds is the voltage they consume, if you dont have testing equipment or the datasheet for your LED's you could use 1.7V to do the math, id also reccomend u look for an instructable here on LED diffussion
codongolev5 years ago
congrats, you ended up in my "led reference" bookmark folder. and 5/5.
xrobinx5 years ago
soo confused. why the hell isnt mine working
Bionex6 years ago
I just bought a soldering iron and a dremel today. I havn't bought any leds yet but im planning to. Where is the cheapest place to??
srilyk6 years ago
Yay, useful! Thanks for the nice instructable... I've just got some LEDs, breadboards, and power... and I'm learning to love the 'lectricity :) (actually I've loved it for a long time, but now I'm learning how to harness it! :D)
I agree that parallel circuits offer redundancy and might prevent catastrophic failure if one LED goes out. However, a properly designed and constructed LED circuit should not fail under normal operating conditions.

It only makes sense to construct a circuit with a single LED per current limiting resistor if the source voltage is 5 volts (for white LEDs) or about 3 volts (for red LEDs). Otherwise, if the circuit operates from 12 volts DC, and contains 3 white LEDs, it would only make sense to place them is a series configuration with one resistor. This is only one circuit example.

Placing all three LEDs in parallel with a resistor for each string would draw 3 times total current, making the circuit much less efficient. This results from all the excess heat disipation from the resistors. However, placing the LEDs in series will only draw 20mA (as opposed to 60mA or whatever drive current was chosen). A high quality LED (such as Nichia Brand) should not fail unless exceeding the data sheet ratings.

I found lots more information like this on the Lunar Accents site: