How to Use LED's




About: Music, chemistry, electronics, etc.


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!

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).

Step 2: More Important Information

Another important thing about all LED's (and all diodes) is that every one of them has exactly two electrodes. These are important to know when you are wiring an LED into a circuit. They are the...

Anode - The p-side which is the longer leg. And the...

Cathode - Which is the n-side and shorter leg.

Since you know these terms you can remember that electricity flows easily from the anode to the cathode but not the other way around.

Step 3: Advantages of LED's

LED's are great for many reasons. First of all, they don't heat up like regular lightbulbs do. This is great because, well, you don't burn yourself. They are also smaller than a lightbulb. Another important thing about LED's is that they run on very low amounts of electricity, which is helpful because it makes them safer to work with (you don't electrocute yourself). Most run on about 20mA.

Step 4: Tips

Just like with everything, there are some tips that are helpful to make sure your LED's work well.

Clip the leads - Simple, I know, but people forget to. This is important because it prevents them from bumping into other parts and messing up your circuit.

Remember which electrode is which - This is a big one because if you don't it won't work at all. It's a diode; current only flows through it one way.

Read the package - Simple again, but each LED requires slightly differnt voltage and ampage.

Step 5: Resistors

It always helps to wire a resistor into your circuit. It will make the LED last longer by dropping the voltage. There are some sites that make it easy to find which resistor you need. My favorite is here.

Step 6: Project Ideas

Now that you have some knowledge of what LED's are you might want some project ideas. It's easy. Anything involving light. And it's not even limited to that. You can check out the LED Contest for some ideas.

The Instructable that I want to enter into the contest is a "Reminder Table" which is a little table with a number of sections (mine has four) that you put things in to remind you to do them. Each section lights up a different color. The idea is that you turn each light on when you have something that you need to remember to do, then off when you accomplish that. I want to use it to remember my practice cards, guitar picks etc.

One of my favorite ideas in the contest is the Star Wars Blaster, which opens up a whole other area of project ideas.

Step 7: Now You're Ready!

With these "Tool Tips" (sorta) and a completed LEDucation (sorry, couldn't resist) I hope you can get out and build some cool LED projects. Remember, I really do appreciate any type of feedback or ratings.



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    91 Discussions


    Tip 1 year ago on Step 5

    Unless you are using a battery like a 2032, you *will* blow the LED immediately. For a normal LED, a 170 to 220 ohm LED will work fine. Put the resistor in series (in line) with the LED. It doesn't matter if the resistor is attached to the anode or cathode. (Meaning between the power and LED or LED and ground.)


    Tip 1 year ago on Step 2

    Look carefully at the ring around the base. The cathode has a flat edge on the base. Some LEDs have the same length leads.

    Dennis Lyman

    5 years ago on Introduction

    Hi, I recently picked up an antique light bulb with a crusifix inside the bulb. Unfortunately, it does not work. I would like to modify the bulb and add an internal led. Any suggestions would be greatly appreciated. Denny


    7 years ago on Step 7

    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.

    ikoneckox3Elephants Are Fat

    Reply 8 years ago on Step 7

    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 :]


    8 years ago on Introduction

    im interested in making some grow lights u sing led's any suggestions,, or books to get,,, indianabob


    8 years ago on Step 7

    Thanks I really learned from this!


    10 years ago on Step 5

    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 ...)

    1 reply

    Reply 9 years ago on Step 5

    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.


    Reply 9 years ago on Step 7

    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.


    Reply 11 years ago on Introduction

    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:
    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.


    Reply 11 years ago on Introduction

    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!


    Reply 11 years ago on Introduction

    I normally use digi-key but I had this LED left over from an earlier project.


    10 years ago on Introduction

    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!)

    1 reply