I had to do this project for many of my young friends who are interested in LED’s but do not know how to go about it.

I also had the same problem but was fortunate enough to get HELP from my friends at

This is not about any calculation or study but a set of proven rules to follow and get results,

which anybody can do if he has the mind to.

Here I have shown you many types of power supply which can be used to glow a LED.

I have also shown here how different types LED's can be made to glow and use it in you project.
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Picture of KNOW YOUR LED

A 15 mm LED has two legs, the long one is the Positive and the short one is the Negative.

It consumes 15 milli Ampere of current and can glow on 3 Volts DC Current, or a 3 volt battery.

LED’s are Diodes and the current can only pass through the POSITIVE side.

Always remember to maintain the POLARITY of the LED, that is (plus to plus) and (minus to minus) otherwise it will not work.

LED is a one way street. Now you know how to connect an LED in your circuit.


Picture of KNOW YOUR LED
If you are interested, here you can see the different parts on an LED.



This set of rules will help to build a Project, follow them.

Here I have shown the Resistors to be used with 6 volts, 9 volts and 12 volts DC.

You can go on adding any numbers of LED's.

Remember that the first line of LED should be in series and  the second line onwards should be in Parallel.

bhuvanamani1 month ago

sorry sir i am not enough . having any converter from 6 v to 4 volt converter

bhuvanamani1 month ago

Hai sir iam manikandan from tamilnadu. i need some answers from LED s. i have 6 volt lead acid batery and 1 watt LED . How many LED connect to the battery.

i think 1 watt LED high britness for 3.7/8 volt DC. so i give connect to 2 LED. so i enough britness this LED . so what i do sir ,help me . my 1 year project pls my thinking pls

Jayhoffmann3 months ago

does this actually work for powering LEDs on AC mains? :

Dipankar (author)  Jayhoffmann3 months ago


HamedH4 months ago

i try to run 100 led with 220v ac but when i connect supply my board is explode

i have some injury in my hand and face tell me where i have mistake?

Dipankar (author)  HamedH4 months ago
You are lucky that you escaped from heavy injury, NEVER connect LED's directly to 220 AC mains.
Here is a circuit follow it......
STEP-3 TL.jpg

hello i want to know one thing .. plz someone tell me what resistor should i use to connect a LED with 220V AC?

Dipankar (author)  bhaskar.p.deka4 months ago

Follow this circuit..............

partha_roy7 months ago

Sir, how to connect 1 watt led on 220 volt ac.

Dipankar (author)  partha_roy7 months ago

You have to use a Transformer, SEE my

24 Watt LED Lamp. and you will get the idea.........

dearshubham8 months ago
Sir i have 21 led i want to run in car please suggest me
Dipankar (author)  dearshubham8 months ago

Use 4 LED's in series and 5 rows.

MikB1 year ago
Your "+" and "-" designations are backwards compared to normal electrical teaching: An LED is a diode and follows the same rules as other diodes. The base of the triangle is "-", and the flat line at the point is "+".

A positive voltage needs to be applied to the "-" terminal, to make it conduct. The "+" terminal goes toward ground.

In the LED physical picture, the LARGE part of the metal (anvil) is the "+" terminal that goes toward ground. Not the "-".
MikB MikB1 year ago
It would help if the intro picture you borrowed from had the designations the correct way round! It's not consistent with the "electronic symbol" directly above it ... Oh well :(
Dipankar (author)  MikB1 year ago
It is the same picture borrowed from
The arrow showing the direction of the current.
MikB Dipankar1 year ago
The + and - are all still backward throughout this tutorial -- it's not helpful to teach people backwards.

The arrows do not indicate direction of current, it's just to show emission of light. A photo diode/photo transistor has arrows pointing towards it to show reception.

Also the "AC" LEDs on a 12v transformer still need a current limiting resistor, otherwise they will be damaged. LEDs don't run on voltage, they need a controlled limited current.
Dipankar (author)  MikB1 year ago
The 12v transformer does not need a resistor as the 6 LED's take care of that.
MikB Dipankar1 year ago
That deserves a good technical explanation, as to how the LED's "take care of" limiting their own current. I'm not sure there is one. That's why you need a resistor, or a current limiting circuit. All you'll do is end up damaging LEDs.
Dipankar (author)  MikB1 year ago
I am not an Electronics engineer but if you see my LED GLOBE posted in June 2011, it has more than 200 LED's and no resistors, but it is still working without a single LED being damaged. So you please explain how is it still working till date? Being too technical sometime does not pay. We are practical people so what works for us is OK with us.

I totally agree!!

MikB Dipankar1 year ago
I looked at your LED globe, it is a fantastic idea, and looks great. I will say though that two people there also commented on the NEED for current limiting in some form, and I agree with them, if this is still working it is down to luck, and not design.

There are better ways to learn about LEDs than by destroying them.
Dipankar (author)  MikB1 year ago
The Positive current flows from the (+) side through LED to the (-) side which is the ground.
andyboy0071 year ago
ok, thanks for the clarification, friend.
Dipankar (author)  andyboy0071 year ago
You are welcome..............
andyboy0071 year ago
Then I saw, just do not understand why in uploaded some (low voltage) resistors have less than 1 watt of power dissipation
Dipankar (author)  andyboy0071 year ago
LED calculator
This is the new version of the single LED series resistance calculator, good for when you have a single LED and need to know "what resistor should I use with my LED?" This calculator determines that for you. The LED series/parallel array wizard is available for those of you who need to do calculations involving more than one LED. The wizard will help you pick the resistors make the connections for any number of LEDs. LED calculator: current limiting resistor value
3.6 = Source voltage
3.5 = diode forward voltage
350 = diode forward current (mA)

The wizard recommends a 1/4W or greater 1 ohm resistor. The color code for 1 ohms is brown black gold.
Link to this solution:;VF=3.5;ID=350 *

calculator rounds the resistance up to the next standard resistor value. You should actually be able to buy a 5% resistor with the value returned by the calculator. ** Power calculations assume use of the standard value current-limiting resistor shown above. Resistor power ratings are chosen based on operating within 60% of the rated value.
LED calculator version 2.0 Copyright 2001-2006, Rob 'linear' Arnold. All rights reserved.
andyboy0071 year ago
hello, I'm brazilian, so forgive my english via google translator.
I would take a question about links with leds 1 watt ...
if they have a watt of power, the resitor attached to them ñ should also have a watt or higher? sorry for the ignorance, I'm new in electronics
Dipankar (author)  andyboy0071 year ago
See step-8. The resistors given for the different DC voltage is correct for a 1 Watt LED.
mathman471 year ago
Nice Instructable, quite useful for those getting started with LEDs. However there is still an error in the schematic. The double arrows indicate that there is light output, not the direction of the current.
Dipankar (author)  mathman471 year ago
OK, I have removed the double arrow as it creates confusion.
MikB Dipankar1 year ago
So now they're not LEDs any more. They're just diodes, with the polarity mislabelled.
Dipankar (author)  MikB1 year ago
I was going through your page and I found that you do not have any Projects posted so you are just a talker rather than a doer. You only love to comment on other people's projects rather do you own??????????
MikB Dipankar1 year ago
"We have a "be nice" comment policy. Please be positive and constructive with your comments"

Did you miss that?

I'll leave you to make your personal comments and insults, I'll leave others to work out whether you have any idea what you're doing.
Dipankar (author)  MikB1 year ago
USING LED's WITH AC TRANSFORMERS. is the heading so it cannot be any other thing, and surely people will understand the meaning.
rimar20001 year ago
This is very useful, Dipankar, thanks for sharing.
Dipankar (author)  rimar20001 year ago
Now you can make your own LED projects.
antoniraj1 year ago
I recently bought few Rigid Strip LEDs of 12 v each. Do they need additional resistors or can be connected directly to battery? It seems that everything is built into it..
Dipankar (author)  antoniraj1 year ago
They do not need additional resistors, use a 12 volts battery or the adopter which came with it, to 220 volts mains.
3 v 750mA - 50 (15mA each )leds who much is it watt ?