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 www.Instructables.com.

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.


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.

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AndyL10 made it!21 hours ago


I would like to add these LED together ( I have 2 pairs which is 4 of them) but I'm not sure if I need additional resistor or just simply connect them in series ( + to - ) then connect to the source which is the 12V battery ( car) . The seller only mentioned this is 12V 9watts LED. Please help !!!

Dipankar (author)  AndyL101 hour ago

Unless I know what type of LED's, I will not be able to answer your question......

AndyL10 Dipankar37 minutes ago

but since we know it is 12V 9watts for each lamp and each lamp contained 2 LEDs therefore can we use this formula P = V x I => I = 9 watt / 12V = .75 A thus .375 A for each LED in one Lamp ?

RaghuR75 days ago
Dear sir which resistot is good for single 1w led to connect 12v battery
Dipankar (author) made it! RaghuR75 days ago

27 Ohms 3.3watt

bhuvanamani3 months ago

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

bhuvanamani3 months 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

Jayhoffmann5 months ago

does this actually work for powering LEDs on AC mains? : http://www.instructables.com/file/FIVRUBHH8TTP6SY

Dipankar (author)  Jayhoffmann5 months ago


HamedH6 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)  HamedH6 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.deka6 months ago

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

partha_roy9 months ago

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

Dipankar (author)  partha_roy9 months ago

You have to use a Transformer, SEE my

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

dearshubham10 months ago
Sir i have 21 led i want to run in car please suggest me
Dipankar (author)  dearshubham10 months ago

Use 4 LED's in series and 5 rows.

MikB2 years 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 MikB2 years ago
It would help if the intro picture you borrowed from http://en.wikipedia.org/wiki/LED had the designations the correct way round! It's not consistent with the "electronic symbol" directly above it ... Oh well :(
Dipankar (author)  MikB2 years ago
It is the same picture borrowed from http://en.wikipedia.org/wiki/LED.
The arrow showing the direction of the current.
MikB Dipankar2 years 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)  MikB2 years ago
The 12v transformer does not need a resistor as the 6 LED's take care of that.
MikB Dipankar2 years 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)  MikB2 years 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 Dipankar2 years 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)  MikB2 years ago
The Positive current flows from the (+) side through LED to the (-) side which is the ground.
andyboy0072 years ago
ok, thanks for the clarification, friend.
Dipankar (author)  andyboy0072 years ago
You are welcome..............
andyboy0072 years 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)  andyboy0072 years 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: http://led.linear1.org/1led.wiz?VS=3.6;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.
andyboy0072 years 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)  andyboy0072 years ago
See step-8. The resistors given for the different DC voltage is correct for a 1 Watt LED.
mathman472 years 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)  mathman472 years ago
OK, I have removed the double arrow as it creates confusion.
MikB Dipankar2 years ago
So now they're not LEDs any more. They're just diodes, with the polarity mislabelled.
Dipankar (author)  MikB2 years 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 Dipankar2 years 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)  MikB2 years ago
USING LED's WITH AC TRANSFORMERS. is the heading so it cannot be any other thing, and surely people will understand the meaning.
rimar20002 years ago
This is very useful, Dipankar, thanks for sharing.
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