This instructable shows how to wire up one or more LEDs in a in a basic and clear way. Never done any work before with LEDs and don't know how to use them? Its ok, neither have I.

***If you have wired up LEDs before, this explanation might seem overly simplistic. Consider yourself warned.***
Remove these adsRemove these ads by Signing Up

Step 1: Get some LEDs

So I wasn't completely honest - I have used LEDs once or twice before for simple applications, but I never really knew what I was doing, and since so many projects on instructables use LEDs, I thought I might as well teach myself and post about it too.

I know that there are many projects already posted that contain information about how to wire LEDs for simple projects - LED Throwies, LED Beginner Project: Part 2 and 9v LED flashlight - teh best evarrr!, but I think that there could still be some use for a detailed step by step explanation about the basics of LEDs for anyone who could use it.

The first step was to buy some supplies and figure out what I would need to experiment with. For this project I ended up going to Radioshack because its close and a lot of people have access to it - but be warned their prices are really high for this kind of stuff and there are all kinds of low cost places to buy LEDs online.

To light up an LED you need at the very minimum the LED itself and a power supply. From what I have read from other LED instructables wiring in a resistor is almost always a good idea.

If you want to learn about what these materials are check out these wikipedia entries:
Power supply


LEDs - I basically just reached into the drawer at Radioshack and pulled out anything that wasn't more than $1 or $2 per LED. I got:

2760307 5mm Red LED 1.7 V
2760351 5MM Yellow LED 2.1 V
2760036 Flasher Red LED 5 V
2760041 2 Pack Red LED 2.6 V
2760086 Jumbo Red LED 2.4V

Power Supply - I really didn't know what I would need to power them so I bought some 9V batteries and some 1.5V AA's. I figured that would allow me to mix and match and make enough different voltage combinations to make something light up - or at least burn those little suckers out in a puff of smelly plastic smoke.

Resistors - Again, I wasn't too sure what I would need in terms of resistors here either. Since I got a whole bunch of different LEDs with various voltages I knew that I would need a couple different types of resistors, so I just bought a variety pack of 1/2 Watt Carbon Film Resistors (2710306).

I gathered up a soldering gun, solder, needle nose pliers, electrical pliers, some primary wire and electrical tape too since I thought they might be useful.

1-40 of 615Next »

We built a couple 76 IR Led lights to run off 12 volt batteries for a portable surveillance system. Once the voltage of the battery drops after several hours the led's fade a bit and then go out but the camera continues to run all night because we're using a dc-dc converter to drop the voltage down to 5 volts.

Is there a way to drop the voltage required for the led's down to 5 volts or even 3 volts by adding a single large wattage resistor to the system? If so what's the formula?

Our other alternative is to add a second battery is series to raise the voltage to 24 volts and then use a dc-dc converter to drop it to 12.

Thanks in advance!

We built a couple 76 IR Led lights to run off 12 volt batteries for a portable surveillance system. Once the voltage of the battery drops after several hours the led's fade a bit and then go out but the camera continues to run all night because we're using a dc-dc converter to drop the voltage down to 5 volts.

Is there a way to drop the voltage required for the led's down to 5 volts or even 3 volts by adding a single large wattage resistor to the system? If so what's the formula?

Our other alternative is to add a second battery is series to raise the voltage to 24 volts and then use a dc-dc converter to drop it to 12.

Thanks in advance!

ElenaG13 days ago

A novice needs help: We just bought a five piece Christmas entryway
set which includes five separate LED light strings and 5 separate
double D cell battery power supplies. I want to convert all to be
powered by one AC adapter I have which has a 12VDC and 2A output. There
is no Watt or Amp ratings on the light strings. My best guess is that
each light is .069 Watts with about 25 lights per string for total of about 125 lights. What is best way to wire these light
strings to the one AC adapter? Thanks in advance for any help


i need to get a contentious 2.9v,200 mah to power my digi-speedometer in bike....can i take it from bike bettery.which resistor i need to use...please help me...

Thanks in advance

banman111 month ago

Hi noahw,

Great article. I converted my outdoor garden light setup from old style halogen bulbs to LED technology. I managed to buy 12v 1 watt LED's from internet for a few bucks.

Thanks so much. :-)

AliS22 months ago

Thanks for this guide, very useful. I'm having an issue in following something, though - ended up burning out a couple of LEDs presumably due to a mistake I'm making.

I've got a 9v battery power source, trying to drive two blue LEDs (3.4-3.8v rated, 20mA) in parallel. I calculated necessary resistor as R = (9 - 3.4) / 0.04 = 140 ohms; to be on the safe side, I used a 180 ohm resistor (brown/gray/brown/gold) in series (battery + to resistor; resistor - to + pole/anode of both LEDs; - pold/cathode of both LEDs back to battery) on a breadboard. Upon connecting the 9V battery the first time, circuit lit; on 2nd time, it then stopped and I smelled distinct LED burnout - after which both LEDs would no longer light, even when connected individually to a 3v (2x AA) source.

Would appreciate any advise re: what I'm doing wrong. Thank you!

BobyF3 months ago

I have one of those a newer one with a led display, I have been powering a 50w smd bead with nothing but a 24v in and a 32v out. Just make sure your input amp. is rated for the beads. Now since you are wiring it in a series be very careful with your v and amp. make sure it`s outputing a constant 3v and slowly bring it up to 3.3v the chinese buck converters will drop in voltage if the supplied amps are not enough. Also when led`s do that it means either too many volts or amps. check your resistors and see if they are smelly, kind of like a burnt carbon smell. Try adding a

DenisĐ3 months ago


I see that this topic is little bit old

But knowledge cant get old :)

my question is: what do i need for connecting few leds in parallel, on my "old" USB lamp(i want to use only housing of this lamp).

Becouase on USB power limit, parallel connection is logical way, or?

I think some kind of step down module is needed that drops 5v to desired 3-3.3v that is needed for led's, for ex.

Power souce is wall socket->USB 5v 1A,

led's are 5730 3-3.3v 150mA,

or 1W beads 3-3.6v 300-350mA.

Is it ok to connect 6 of 5730 led's, and/or 3 of 1W led's in parallel?

Is there something else needed for make this working?

P.S. this "old" usb lamp has 13 led's(those small ones) and each has resistor in front, but after short time they start to rapidly blinking and at the end stop working. What that mean, led's are dead, or resistors are not ok, or what?

tnx, and sorry for a little long post :)


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!!!
ronym83 ahwang4 months ago

6 volt battery sometimes have more than 6 volt

( it's depend on battery state... it's full... or near empty )

so we must measure the exact voltage of battery using volt meter

if the voltage of battery is... say 6,5 volt

devide it by two we get 3,25 volt...

that's why your LED are too hot... because you over voltage it


just like 12 volt battery which can be 10,7 to 12,8 volt

( it's depend on charge state of battery )

it also can be 14 volt ( if the battery are connecting to the charger )

cellis6 ahwang3 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.
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
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

are you sure without resistor LED can burn in few second ? ever try it ?

i ever connecting 4 series of 3 watt LED to 50 AH battery for 3 hours

yes the LED is hot ( even LED are producing heat, that's why we still need proper heat sink+fan if necessary ), but they are not burn

i measure voltage in every LED... 3,0 - 3,2 volt each

so it's safe because its around LED rating at 3,0-3,7 volt


for 20mA white LED, we have different case

because it's voltage rating are only 3,0-3,4 volt


car battery have stationary voltage at 12,6-12,8 volt

so devide by 4, we get 3,15 - 3,2 volt

but if car battery jump to 14 volt ( because alternator are charging battery )

we get 3,5 volt in each LED

that's why in 20mA white LED it's a bit riskier

( 3,5 volt in 3 Watt LED it's not a big deal

because it's less than max rating of 3,7 volt )


using resistor to limiting current ?

it's useless too if battery jump to 14 volt

I = V / R

because R are constant

but V are up... so I must be up in value

( so it's not safe either just using resistor )

Can there a difference in the brightness if you use series ? say R= (6v-8.0)/.02mA
I am such a beginner!
sushil0106 months 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.

djspincycle7 months ago

Hi Noah, Some LED spec sheets list "Foward Voltage" and "Reverse Voltage". Which is the voltage that is correct for supplying to the LED?

Forward Voltage is the volatage when it lights up. reverse voltage is the limit to what it can take hooked up backwards. Hint: If you want to hook an LED to AC, make sure that the forward and reverse are both 1.4X the rated AC voltage. For example, if you wnat to hook up a series of 3V leds to make christmas lights and run them off 120VAC, you could use 56 lights, or 50 lights and a resistor.

thinders7 months ago

i followed the steps in this project ....

and posted a comment (with a pic) that my LEDs have all gone "dim" ....

Can someone take a peek at what I posted and advise me on what I did wrong ...thanks

eortega810 months ago

"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)." Can someone please explain why he needs to attach a resistor to each LED if all together, the LEDS use up the 12 volts?

Leds work differently than incandescent lamps. first it is a semi conductor, when the voltage is applied, current rushes through the Led as if there was no resistance. incandescent bulbs increase in resistance as they warm up if I remember correctly. more current equals more power and consequently more heat. thermal runaway kills semiconductors.

dudes eortega89 months ago
Because the amps of a car battery would blow out an led instantly. It's not all about volts it's also about amps. Hope this helped.
his_bevness8 months ago

Brilliant Instructable thanks, from a grateful noob!

djmaxpaul8 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.

chuchomalaga8 months ago

thanks a lot for your explanation, may I use it in my classroom? Easier you explain, easier you understand. And best of all, think with the hands.

lgarcia rivera10 months ago

thanks, its very funny and easy

paci6310 months ago

any thing new

paci6311 months ago

thank u so much it was very very helpfull for from all sides

bradix1411 months ago
noahw, thanks for the great explanation of the basics!
jdeth1 year 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 jdeth11 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?
If the battery is 1.5 volts and the led has a voltage drop of 1.7 volts, then how is it lighting? Am I unaware of something?
1.7 is probably max.
JCA1001 year ago
What a Brilliant Tutorial. I have only just discovered Instructables and this is just what my RMT students need for their GCSE Lighting project. Thanks for all your hard work. We will make good use of it.
jsaurabh1 year ago
Thanks for such a wonderful instructable. After this, I too am not afraid of LEDs. Now, they are my friends too.
i have a big problem i think ull solve it perfect.
i had connected 50 leds parallel to 6 volt battery its working without any problem for 5 hours, i didnt use resisters is there any problems
this has been discussed all over the web. The more leds you use in parallel the less resistance (resistor) is needed before the voltage source. if you used one led and a voltage source of 6volts it will get hot and eventually pop. you can acutally buy led holiday lights from stores that will have hundreds in series or parallel. If you plug it into the wall it will work just fine but if you take one of the leds out of the circuit and plug it into the wall it will pop in no time. I am not onehundred percent sure if what I am saying is correct but I have read it on multiple threads, i have never tested it out.
What are the voltage and current requirements of your LED's??
donmatos2 years ago
Thanks for such valuable information. For me it was like rain falling on the arid soil of the Brazilian northeastern backlands, lowering the dust that prevented us from seeing our crops. Now, I can pick some fruit. But I have a question that may be the subject of his next insructables: AC 220V in, I could turn (turn) 70 LEDs without using resistors? Thanks be to find time to answer, if not, thanks anyway.
1-40 of 615Next »