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.***
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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.

Step 2: The LED

LEDs come in different sizes, brightnesses, voltages, colors and beam patterns, but the selection at Radioshack is pretty small and so I just picked up a couple different LEDs from what they had in a few different brightnesses and voltages. I kept close track of what LED was what voltage because I didn't want to accidentally send too much current through one of the low voltage LEDs.

The first thing I did with the LEDs was figure out which wire (its called an electrode) was positive and which was negative. Generally speaking the longer wire is the positive electrode and the shorter wire is the negative electrode.

You can also take a look inside the LED itself and see whats going on. The smaller of the metal pieces inside the LED connects to the positive electrode and the bigger one is the negative electrode (see picture below). But be warned - in the LEDs I picked up I didn't always find this to be true and some of the LEDs had the longer electrode on the negative when it should be on the positive. Go figure - its OK though, if it didn't light up I just flipped it around.

Once I knew what was positive and what was negative I just had to remember what the voltage of each LED was.

All my LEDs recommended 20mA of current. 20mA is standard for most LEDs.

Step 3: Power supply

To make the power supplies I just soldered some wire onto the ends of the batteries I had bought so that I could easily attach the LEDs to them. The 9V battery served as my 9V power supply, one AA battery made a 1.5V power supply and three AA batteries bundled together made a 4.5V (1.5V + 1.5V + 1.5V = 4.5V) power supply. I didn't use alligator clips on the ends of the wire, but they would have been helpful here.

Step 4: Resistors

I opened up the assortment pack to find that resistors aren't labeled with what value they are. The pack said it contained a whole bunch of different resistors from 100 ohms to 1 Meg ohm so I set out to see what was what. When I poked around online I found that all resistors have a coding system on them that tells you what value they are.

Here are two pages which explain in depth about how to calculate resistor values.

Do it yourself
Have it done for you

I'll go through the examples of how I calculated the values myself in the next few steps when I start wiring up my LEDs.

For the time being I just admired their little colored stripes and moved on to trying to get just one LED to light up.

Step 5: One LED, no resistor

I thought that I would start as simply as I possibly could - just one LED with no resistor. First I had to decide what power source to use and which LED to light up. This may seem obvious, but this was my first time through so I might as well be as clear as possible...

LEDs require sufficient voltage to light them. Sometimes if you give them too little voltage they wont light at all, other times they will just shine dimly with low voltage. Too much voltage is bad and can burn out the LED instantaneously.

So ideally you would like the voltage of the LED to match the voltage of your power supply, or even be slightly less. To do this you can do a couple of things: change your power supply voltage, change the LED your using, or you can use a resistor that allows you use a higher voltage power supply with a lower voltage LED.

For now I just wanted to get one lit up so I chose my the power supply that had the lowest voltage - the single AA battery which outputs 1.5V.

I chose to light the red 1.7V LED since the battery outputs 1.5V and I knew I wouldn't kill the LED with too much power.

I wrapped my positive wire from the battery to the positive electrode of the LED and wrapped the negative wire from the battery to my negative electrode and presto - let there be LED light!

This first experiment was pretty easy to do - just some wire twisting and enough knowledge to know that the 1.5V power supply would light the 1.7V LED without need a resistor.

Step 6: One LED with a resistor

It was just a coincidence that I bought an LED that was 1.7V and that it ended up working being able to be powered by my 1.5V power supply without the use of a resistor. For this second setup I decided to use the same LED, but up my power supply to the three AA batteries wired together which output 4.5V - enough power to burn out my 1.7V LED, so I would have to use a resistor.

To figure out which resistor to use I used the formula:
R = (V1 - V2) / I

V1 = power supply voltage
V2 = LED voltage
I = LED current (usually 20mA which is .02A)

Now there are lots of calculators online that will do this for you - and many other instructables reference this as a good one, however, the math really isn't too hard and so I wanted to go through the calculation myself and understand whats going on.

Again, my LED is 1.7V, it takes 20mA (which is .02 A) of current and my supply is 4.5V. So the math is...

R = (4.5V - 1.7V) / .02 A
R = 140 ohms

Once I knew that I needed a resistor of 140 ohms to get the correct amount of voltage to the LED I looked into my assortment package of resistors to see if I could find the right one.

Knowing the value of a resistor requires reading the code from the color bands on the resistor itself. The package didn't come with a 140 ohm resistor but it did come with a 150 ohm one. Its always better to use the next closest value resistor greater than what you calculated. Using a lower value could burn out your LED.

To figure out the color code you basically break down the first two digits of the resistor value, use the third digit to multiply the first two by and then assign the fourth digit as an indicator of tolerance. That sounds a lot more difficult than it really is.

Using the color to number secret decoder website found here, a 150ohm resistor should have the following color code...

Brown because the first digit in the value resistor I needed is 1
Green because the fifth digit is 5
Brown because in order to get to 150 you have to add one 0 to 15 to get to 150.
Gold - the resistors I got all have 5% tolerance and 5% is represented by gold

Check out the decoder page link above if this isn't making sense.

I looked through all the resistors, found the one that was brown, green, brown, gold, and wired it in line on the positive electrode of the LED. (Whenever using a resistor on an LED it should get placed before the LED on the positive electrode).

Low and behold, the LED lit up once again. The 150 ohm resistor stopped enough of the 4.5V power supply from reaching the 1.7V LED that it lit up safely and kept it from burning out.

This is just the process that I went through to figure out what resistor to use with my particular LED with my particular power supply. You can easily use the formula above to figure out what value resistor to use with whatever LED and power source you happen to be using.

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.

Step 8: Wiring up multiple LEDs in parallel

Unlike LEDs that are wired in series, LEDs wired in parallel use one wire to connect all the positive electrodes of the LEDs your using to the positive wire of the power supply and use another wire to connect all the negative electrodes of the LEDs your using to the negative wire of the power supply. Wiring things in parallel has some distinct advantages over wiring things in series.

If you wire a whole bunch of LEDs in parallel rather than dividing the power supplied to them between them, they all share it. So, a 12V battery wired to four 3V LEDs in series would distribute 3V to each of the LEDs. But that same 12V battery wired to four 3V LEDs in parallel would deliver the full 12V to each LED - enough to burn out the LEDs for sure!

Wiring LEDs in parallel allows many LEDs to share just one low voltage power supply. We could take those same four 3V LEDs and wire them in parallel to a smaller power supply, say two AA batteries putting out a total of 3V and each of the LEDs would get the 3V they need.

In short, wiring in series divides the total power supply between the LEDs. Wiring them in parallel means that each LED will receive the total voltage that the power supply is outputting.

And finally, just some warnings...wiring in parallel drains your power supply faster than wiring things in series because they end up drawing more current from the power supply. It also only works if all the LEDs you are using have exactly the same power specifications. Do NOT mix and match different types/colors of LEDs when wiring in parallel.

OK, now onto to actually doing the thing.

I decided to do two different parallel setups.

The first one I tried was as simple as it could be - just two 1.7V LEDs wired in parallel to a single 1.5V AA battery. I connected the two positive electrodes on the LEDs to the positive wire coming from the battery and connected the two negative electrodes on the LEDs to the negative wire coming from the battery. The 1.7V LEDs didn't require a resistor because the 1.5V coming from the battery was enough to light the LED, but not more than the LEDs voltage - so there was no risk of burning it out. (This set up is not pictured)

Both of the 1.7V LEDs were lit by the 1.5V power supply, but remember, the were drawing more current from the battery and would thus make the battery drain faster. If there were more LEDs connected to the battery, they would draw even more current from the battery and drain it even faster.

For the second setup, I decided to put everything I had learned together and wire the two LEDs in parallel to my 9V power supply - certainly too much juice for the LEDs alone so I would have to use a resistor for sure.

To figure out what value I should use I went back to the trusty formula - but since they were wired in parallel there is a slight change to the formula when it comes to the current - I.

R = (V1 - V2) / I

V1 = supply voltage
V2 = LED voltage
I = LED current (we had been using 20 mA in our other calculations but since wiring LEDs in parallel draws more current I had to multiply the current that one LED draws by the total number of LEDs I was using. 20 mA x 2 = 40 mA, or .04A.

And my values for the formula this time were:

R = (9V - 1.7V) / .04A
R = 182.5 Ohms

Again, since the variety pack didn't come with that exact value resistor I attempted to use the two 100 Ohm resistors bundled together in series to make 200 Ohms of resistance. I ended up just repeating the mistake that I made in the last step again though, and wired them together in parallel by mistake and so the two 100 Ohm resistors only ended up providing 50 Ohms of resistance. Again, these LEDs were particularly forgiving of my mistake - and now I have learned a valuable lesson about wiring resistors in series and in parallel.

One last note about wiring LEDs in parallel - while I put my resistor in front of both LEDs it is recommended that you put a resistor in front of each LED. This is the safer better way to wire LEDs in parallel with resistors - and also ensures that you don't make the mistake that I did accidentally.

The 1.7V LEDs connected to the 9V battery lit up - and my small adventure into LED land was completed.

Step 9: Extrapolation

While I didn't actually end up making anything besides a couple of lit LEDs, this information can be used to make all kinds of cool things!

The take away concepts hopefully were:
- Power a whole bunch of different value LEDs using the same basic principals.

- Figure out what is the positive electrode and what is the negative electrode of an LED by looking at it and testing it.

- Use resistors, or combinations of resistors wired together in series or in parallel to supply the correct amount of power to the LED.

- Make calculations to determine what resistor is needed using the formula, or using web sites that do it for you.

- Wire LEDs in series or in parallel depending on the application.

- Make LEDs light up!

This was the most basic kind of walk through for LEDs possible - and I learned a whole lot along the way. LED arrays and wiring schemes can get significantly more complicated - but for the most part, LEDs are pretty simple to work with, and with relatively little knowledge I was able to light them up - all be it if I sent a little too much juice through them towards the end of the experiment. I don't fear the LED now. They are my friends.

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Ok, trying to light 3 x 1.5w infared leds from a USB cord (5w). What would be the best way to hook them up? Series or Para? What resisters would I need (if needed) Thanks!

ElenaG1 month 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

JohnL8 ElenaG24 days ago

It's a tough question because what you exactly have is unclear. You mentioned "double D cell battery power supply". Is it just one 3.6V (or other voltage value depending on the battery type) or more than one "double D cell battery" connected either in series or in parallel together? Does each LED string has any electronic components (e.g. a driver) connected or simple LED?

Anyhow, if you find some sort of circuit somewhere on the LED string, it would be complicated to make any change unless the battery power supply is in fact around 12V, then connect the 5 string in parallel. If visually you only see LED on each string and if you have a multimeter, measure the voltage of the power supply. Depending on the measured voltage, the wiring may be very easy or complicated.

Assume measured around 3V, then connect 4 strings in series, +-+-+-+-. The fifth string requirs resistor.

Assume measured around 6V, then connect each of 2 strings in series, +-+-; then connect the two "2-strings-in-series" in parallel. The fifth requires resistor. Based on the same procedures, you can figure out connections for other voltage options.

In case you want to power all the 5 strings, current-limiting resistors are needed or re-assemble the strings to have equal length unless the battey supply is around 12V.

AliS23 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!

JohnL8 AliS225 days ago

If the 9V power supply is from battery, your connection works with drawbacks. If the two LED are from the same manufacturing batch, there will be less potential problem. If they are from different batches, one may draw more current than the other and one of LED will burn or weakened. The second time power is connected, the already-weakened LED couldn't handle more stress and blow. Now all the current will be consumed by the survived LED. With double current, it burns out as well.

In case the 9V is from an AC adapter (wall-wart), your LED may be burnt due to higher than anticipated current. A 9V AC adapter is guaranteed to provide a minimum 9V at a maximum load specified by the adapter. As the two LED only draw 40mA, the supply voltage could be 11-13V or even higher. And your LED will be blown out eventually as the current supplied to each LED is higher or way higher than 20mA. It also have the same problem as of battery.

That is why separate resistors are required to connect to every LED string connected in parallel, either each string consists of just one LED or a few LED, to avoid what you have experienced.

need help! Trying to wire up 4 led (night light brightness lights) to replace my (4) conventional lights. Would like to wire them all together and be powered by a 12 Volt adapter. I have no experience in doing this. Anybody willing to chime in? Thanks folks..

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!


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

banman112 months 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. :-)

BobyF4 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

DenisĐ4 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 ahwang5 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!
sushil0107 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.

djspincycle8 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.

thinders8 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

eortega811 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 eortega810 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_bevness9 months ago

Brilliant Instructable thanks, from a grateful noob!

djmaxpaul9 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.

chuchomalaga10 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 rivera11 months ago

thanks, its very funny and easy

paci6311 months ago

any thing new

paci631 year ago

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

bradix141 year 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 jdeth1 year 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.
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