How To Use LED's
7 Steps
NOTE: THE FIRST THREE STEPS ARE AN INTRO.THOSE OF YOU WHO ALREADY KNOW ABOUT LED's SHOULD SKIP TO STEPS 4 AND 5 FOR THE TIPS.

I've been noticing that a lot of people (not people on instructables, but people interested in electronics in general) don't really know about LED's. No one in my science class at school had ever even heard of them. This is an easy introduction to LED's that should teach you the basics. It's good if you're interested but have no idea where to start. I also thought this would help out anyone wanting to enter the contest, but it took me a while to finish.

Remember, (As always) feedback and ratings (positive or negative) are always appreciated!
FOR MORE INFORMATION SPECIFIC TO WIRING, YOU CAN SEE NOAHW'S INSTRUCTABLE "LEDs FOR BEGINNERS"
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## Step 1: Name/Background Info

LED's. So common on Instructables. What the heck are they?

LED is an acronym for Light Emitting Diode. Well, you ask, what on earth is a diode.

A diode is a device that, in simplest terms, allows electricity to flow through one way but not the other. Those of you who are knowledgeable about mechanical things could think of it as sort of a check valve. If you have no mechanical knowledge, disregard that last sentence.

Now that you know what a diode is, an LED is just one that emitts light (But you could probably figure that out just from reading the name).
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Mike_MK says: Sep 15, 2011. 4:32 AM
A few tips;
Often LED's have equal length 'legs', so to work out which one is which, look closely inside the plastic with a mag glass, the negative is the side with the bigger surface area, or looks like an upside-down 'L'.
The power supply is often 12 volts DC (a battery, or transformer). But can be 3 volts to about 30 volts DC, (Normally.)
The current limiting resistor is very necessary, if you want the LED to last any time, and a proven value to use with 12 volts, is 470 ohms. This will limit the current to 0.025 Amps, i.e. 25mA. This is using the common formula from 'Ohm's law', V/A=R, so in this case, 12/0.025=480 ohms.
It is best practice to fit it between the Positive of the LED and the power supply's positive terminal.
LED's can be bought in various shapes, round, square, rectangle, and in various colours, red, green, yellow, orange and blue. Hope the photo helps.
Elephants Are Fat says: Mar 25, 2009. 12:33 PM
do you where you can get a large amount of LED's?
ikoneckox3 says: Jan 29, 2011. 11:25 PM
i bought 100 with 100 resistors on ebay for about \$2.00, and after shipping (hawaii) it was \$7.00 they seem to work fine too- and if you dont want to buy online, you might be able to try LED christmas lights :]
asdftzui says: Jan 2, 2011. 4:51 AM
go to the store dude.. u will find large amount of LED's..ok..
tanmanknex says: Apr 23, 2009. 4:55 PM
http://www.moddersmart.com/en/loose-5mm-led-blue.html
has very low prices on l.e.d.s compared to other stores.
indybob says: Nov 18, 2010. 8:43 AM
im interested in making some grow lights u sing led's any suggestions,, or books to get,,, indianabob
J3PPiSH says: Aug 6, 2010. 3:13 PM
Thanks I really learned from this!
mr_bandit says: Nov 23, 2008. 1:08 AM
The resistor is to limit the CURRENT, not the voltage. The two things this article is lacking is a schematic and a simple picture of the circuit soldered up. The long lead is on the voltage plus(+) side and the short on the minus (-) side. The resistor is in series with the LED, on either side of the LED: (+) --- resistor --- long lead --- short lead --- (-) or (+) --- long lead --- short lead --- resistor --- (-) A resistor in the range of 1K to 10K is usual. Note some LEDs connected directly to a watch battery will work without a current-limiting resistor, but it is iffy and not good practice. (more in-focus pictures would be nice ...)
NiftyJunk says: Oct 16, 2009. 8:50 PM
Yeah, its that little flower button on the camera. You know, for close ups. I was so happy when I found out what that little function does.
Schisler7 says: Feb 4, 2008. 9:40 PM
How much are LEDs from Radioshack? Is there any better place to get them?
kadris3 says: Sep 30, 2009. 8:32 AM
send me an s.a.s.e. and I'll send you some. see below. Uncle Cy
Swishercutter says: Jun 1, 2009. 10:40 AM
Ebay...I use Digikey for new specific parts but for the price you can't beat ebay. In my case the person sent the resistors (5 band precision ones) for free when I bought the LED's. Not that resistors are expensive but it's still nice to not have to buy some.
burzvingion says: Feb 5, 2008. 1:07 AM
It's usually only prudent to buy anything from radioshack if you absolutely need it immediately and there are no other brick-and-mortar stores in your area that will sell said item. Almost anything you buy there, from LEDs to batteries to plastic project enclosures, will be marked up around 500%. It's a little bit like buying groceries at a gas station, except worse, because it happens to be the only gas station in town.

Buying parts online from wholesalers and surplus outfits is usually the cheapest way to go. Standard LEDs can be had for around 5 to 10 cents each, while high brightness ones will usually be a little more. Blue/violet, white, and UV LEDs are the most expensive, but can often be found for \$0.75 or less each. Some places to look include:
http://www.allelectronics.com/
http://www.mpja.com/
http://www.mouser.com/
http://www.digi-key.com/
Then theres eBay. Search and you shall find. There are a lot of good deals and hard to find items around on eBay that most people never think to look for.
kadris3 says: Apr 5, 2008. 11:09 AM
if any student is broke, but wants a few leds to play with, i would be happy to send them to him. send me a stamp and some of my slow movers, pulls, or drops will be sent for your playing pleasure. they will all light when they leave here. when an led hits the floor, i cannot tell which bag it came from. i know the color, but not the intensity. please tell me your grade or yr in school. i'm happy to help but don't appreciate getting lied to or ripped off. also on the website is ohms law instruction fr figuring resistance. questions are a click away under "ask uncle cy". u don't need a bundle of money if u know an old fart like me! unclecytheledguy.com
Gjdj3 (author) says: Feb 5, 2008. 5:08 AM
I normally use digi-key but I had this LED left over from an earlier project.
psycholily says: Jan 3, 2009. 2:53 AM
so... if i have, say, solar LED path lights, and I want to swap out the white LED for an amber one, I need to..... do something? because they're different? aargh. can anyone tell me? (also, this has been so useful to me!)
kadris3 says: Sep 30, 2009. 8:31 AM
on a 3 vdc supply ,you need a 47 ohm resistor.Uncle Cy
Gjdj3 (author) says: Jan 3, 2009. 8:18 AM
It shouldn't be too hard to do. Amber and white have similar voltages I think, so you could probably just go right ahead and swap without any resistor. On the other hand though, if you don't want any risk of frying the LED you could just try adding a small resistor to the positive leg of the amber LED.
psycholily says: Jan 4, 2009. 2:58 AM
thanks. so what am I looking for when I go to get the resistor? what value? (sorry, annoying questions, and I don't even know if i'm asking the right ones) the LEDs available to me in white are 1: 3mm 1500mcd 3.5v DC @ 30 mA 2: 3mm 5000mcd 3.4v DC @ 25 mA 3: 5mm 2000mcd 4.0v DC @ 30 mA 4: 5mm 8000mcd 4.0v DC @ 30 mA 5: 5mm 16000mcd 3.0v DC @ 20 mA and lord knows which type will be in the light in the first place. the voltages are all different. then the amber ones are: 1: 5mm 6500mcd 2.0v DC @ 20 mA 2: 5mm 7000mcd 2.0v DC @ 20 mA the lights run on AA batteries, so I assume there's already some sort of resistor in there? sorry, I'm totally confused, I think i'll give this up as a bad job and just leave the LEDs the colour they come to me as -_-;;
Gjdj3 (author) says: Jan 4, 2009. 7:38 AM
Well If you were going to replace white with amber it shouldn't be too hard. There are three resistors that would probably work with the amber light. I would start with the highest first so that there's no risk of burning out the LED. Then, if it doesn't work you can try the next lower resistor. The three that would probably work would be... A. 100 Ohms B. 75 Ohms C. 51 Ohms Just solder the one you choose to the positive leg of the new LED. And remember, if you can't find an exact match on the resistor, just choose one close to it.
psycholily says: Jan 4, 2009. 3:22 PM
Thanks so much! I'll give it a shot, and if mishaps occur, well, LEDs are cheap.
Gjdj3 (author) says: Jan 4, 2009. 7:32 PM
Cool! Tell me how it goes.
grantdevine says: Dec 28, 2008. 6:13 PM
So do I need to us a resistor when only attaching one LED or is it only a reccomended thing or is it totally unnesecary
Gjdj3 (author) says: Dec 28, 2008. 7:23 PM
It depends on the power source and led. For example, 3V to an red led wouldn't require a resistor. On the other hand 9V to the same led would need a resistor otherwise the led would fry.
kadris3 says: Sep 30, 2009. 8:16 AM
red LEDs usually have a nominal forward voltage of 2.1 vdc. you do need a current limiter. 47 ohms works well here. for an extra measure of safety you could use a 55 ohm or slightly larger. the higher you go the further you get from speck brightness. I hope this helps. Uncle Cy
skrubol says: Jun 4, 2009. 6:39 AM
What sort of red LED's are you using that work with 3v? Vf of normal red LED's is 1.8v I believe. Some LED's have built in current limiting resistors, meant to run them at 3 or 5v, which it sounds like you have. Normal red LED's will last seconds at 3v or pop right away. You really should learn some more about how LED's work before posting information about them.
McGrep says: Jun 3, 2009. 6:55 PM
Normally, I have a basic understanding of electrical components, however LEDs are especially not my cup of tea. That's why I ended up eradicating the few LEDs I had... I should have stopped with the 9V batteries when they started shorting out... that was not a brilliant idea on my part. I had dissected an old universal remote and burned up the visible LED, while using an infrared LED (with a lower voltage) connecting the cathode to the positive terminal and anode to the negative. I've got a ways to go!
grantdevine says: Dec 28, 2008. 8:59 PM
That would explain why my LED's have a tendency to explode on me XD
E D E N says: Jul 23, 2009. 10:05 PM
So, how exactly do you find the mA of an LED? Is it just from general assumption or like an actual measurement from the LED ?
Gjdj3 (author) says: Jul 23, 2009. 10:16 PM
Different types of LEDs will have different mA ratings. You can generally tell by looking on the package.
E D E N says: Jul 25, 2009. 12:05 PM
Alright, thanks
iain0070 says: Oct 19, 2008. 4:31 AM
how do u tell which is positive if you have salvaged it and both ends r th same length?
Gjdj3 (author) says: Oct 19, 2008. 8:54 AM
The negative side should have a flat edge and the positive side should have a rounded edge.
Swishercutter says: Jun 1, 2009. 10:27 AM
You are correct. The cathode should have a flat edge. When I was working in industry (electronics manufacturing) the assemblers were told not to trust the flat side or the longer leg. So how did they tell? If you look inside the LED you can see one side is larger and looks a bit like a "flag", this side is the cathode...the flag points to the positive. So if you have salvaged parts this is a good way to tell for sure, especially when the leg is cut or the case is embedded.
Rotten194 says: Jul 8, 2009. 6:59 PM
Actually, some LED's are backwards in this respect. Most aren't though.
theRIAA says: Feb 4, 2008. 5:35 PM
the only thing i've never figured out is, what mA is the LED running at if I don't use a resistor? is it calculable? how do you run resistors in parallel, and do you have to know the mA to drop voltage? and where can I get some of those sweet blurry LEDs?
skrubol says: Jun 4, 2009. 6:44 AM
No, you can't calculate the current from the voltage you feed to the LED. Anyone who tells you otherwise is incorrect and setting you up for failure. You need a resistor or something to control the current to the LED, it will not run at 20mA if you just give it some voltage. If you give an LED a constant voltage, at best its light output will not be stable (as it warms up it will get brighter,) and at worst it will fail. You also won't be able to get the maximum output out of it without risking killing it. Also not all LED's are 20mA. I've got an LED that uses 2800mA, and several in the range of 350-1000mA. These are a different class of LED (power LED,) but there are all different sizes (both physically and power handling) of LED.
kadris3 says: Dec 5, 2008. 7:58 AM
all single LEDs draw 20ma, unless they are a special low amperage one. the voltage varies with color. think of the resistor as a current limiting device. old ohms law applies. e=ixr. e is volts. i is amps. r is resistance. since i has to be in amps, 20ma is .02. for red, yellow,amber, and orange use 2.1 volts. for white,UV,
blue and green use 3.4 volts. IR are by themselves and about 1.2 vdc. as an example 3 white leds in series are 10.2vdc. if a 12vdc supply is used 1.8 vdc, left to be dissapated, /.02 =90 ohms. 100 works great. for 13.8 vdc use 180 ohms. for a brighter light parallel up several strings. best of luck to all. Uncle Cy
wccolvin says: Sep 29, 2009. 10:04 PM
I am confused,I thought you had to take your Source Voltage of 12 Volts and Divide it by your .020 Amps of Current to get the Resistance to supply the correct Current through your Series Circuit.that would be 12 Devided by .020 which equals 600 Ohms Resistance.I am also confused on the Power is equal to Source Voltage times your Circuit Current.So if I have a 3 Volt LED with .700 Amps of Current that would give 2.1 Watts of Resistance.That just seems like a large Wattage for only 3 Volts.Could you please help me understand where I am getting Confused.Thank you very much,Sincerely Charles.
kadris3 says: Sep 30, 2009. 8:02 AM
hi Charles,
thanks for your questions. first watts is power not resistance. a 3vdc led that draws .7 amps is indeed a 2.1 watt burner.
my intent was to determine the value of the current limiter. you only use the difference between supply and forward voltage for the LEDs. if you have 3 white LEDs in series that's a forward voltage of 10.2 vdc. if the supply is 12vdc then 12 -10.2=1.8volts. 1.8 vdc / .02=90 ohms. 100 ohms would work perfectly. if the supply is 13.8 then 180 ohms is needed.
think of the string of LEDs as one entity. it is limited to .02 amps (20 ma). we only need the difference between the supply and how many volts the string of LEDs "eats". we are not figuring the resistance of the whole string, only the missing part.
P=E X I. no resistance in the formula for power. you seem to have ohms law down.
you are trying to figure the resistance of the entire string which is not what we were intending to do. you only need to figure the missing part which is easy to calculate. we know the current (.02 - limited by properly biased diodes) and the supply minus the total voltage of the Diode string. this gives us the voltage of the unknown value we seek. then basic ohms law and we have the needed resistance of the current limiter.
if you are still confused please let me know and i'll try again. thank you
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