LED Basics
100 Comments


In the late 1800s, Thomas Edison invented
the first commercially viable light bulb. Light bulbs like this work by passing large
amounts of current through a thin filament, which is basically a wire. The filament gets so hot that it starts glowing,
and emitting light. This process is very inefficient – less than
5% of the energy going into the bulb gets turned into light – the rest gets turned into
heat. A much more efficient source of light is a
light emitting diode, or LED. LEDs basically contain two specialized semiconductors
that are stuck together, and when you apply a large enough voltage across them, they emit
light from a process called electroluminescence. There is some heat produced, but overall the
process is a lot more efficient, and you can get a lot of light from a very small device. On average, they last for over 10 years of
continuous usage, so you can see why they are popular. Nowadays we have LED flashlights, LED street
lamps, billboards and even LED light bulbs. But you don’t have to be as big as Sony to
create LED circuits. In this video I’m going to show you the basics
of how to use an LED at home. First, get some LEDs. You can buy them anywhere that sells electronics,
but Amazon has them really cheap, and you can get dozens for just a few dollars. I’ll put a link in the video description section. I recommend getting some resistors to go along
with them, and I’ll explain more about that in an upcoming video. So every LED has 3 important things you need
to know. The polarity, the forward voltage, and the
maximum current rating. Let’s start with polarity, and this basically
means which way do you connect the LED in your circuit. All LEDs will have two leads, an “anode” and
a “cathode”. The anode and cathode are sometimes abbreviated
A and C. The anode is the side that conventional current will flow into. In other words, you connect the positive side
of your power source to the anode. The cathode is where conventional current
will flow out from. So you will connect your negative side of
your power source to the cathode. For standard 5mm LEDs like this, there are
two easy ways to figure out the polarity. The anode will have a longer lead, and the
cathode will have a shorter lead. Also if you look carefully, you’ll see that
one side of the case has been filed down flat. The flat side is the cathode, and the round
side is the anode. So in this example I connected the positive
side of a power supply to the anode, and the negative side of the supply to the cathode. The LED lights up as expected. If you get the polarity wrong your circuit,
don’t worry, for low voltage projects the backwards LED blocks current from flowing,
and it just doesn’t turn on. Ok, now let’s talk about the forward voltage
of an LED. All LEDs need a certain voltage across them,
in the right direction, before any current can flow and they start emitting light. This particular white LED I’m using has a
forward voltage of 3 volts, so we need around 3 volts before it can do anything interesting. With the supply set to 0 volts the LED stays
off. With the supply set to 1.5 volts, it’s still
not enough to turn the LED on. But as we get closer to 3 volts, the LED reaches
full brightness. Every LED will have a forward voltage that
is a little different, and here are some rough guidelines of what you can expect from different
LEDs. Once the LED is on, there will be a relatively
constant voltage drop across it. Next, let’s talk about the maximum current
limit of LEDs. In this example, I was using a special feature
of my power supply to limit the current going through the LED to a maximum of 30mA, which
is about as much as this LED can handle. But what happens if I take my foot off the
brakes? I’m going to set the power supply to 7.5 volts
and I’m going to remove all current limits. Let’s see what happens! So if you significantly exceed the LED’s forward
voltage rating, massive amounts of current will flow through the LED, and there’s nothing
to stop it from blowing itself up. Obviously don’t do this at home, it’s actually
possible for LEDs to explode, sending tiny chunks of plastic and metal flying at your
face. You don’t want to end up looking like this! Now you see why in my video on voltage a 9
volt battery was enough to instantaneously kill an LED – there needs to be something
to limit the amount of current to a safe value. The current rating on every LED will be different. For example this high powered LED module can
easily handle 100 milliamps, but in general the standard 5 mm LEDs you are going to be
playing with at home are rated for 20 milliamps. So what do you do if you want to limit current,
and don’t have a fancy adjustable power supply? You can use a thing called a resistor! And these literally cost a few pennies. I’ll talk more about resistors and resistance
in my next video which will be linked here. In the meantime, leave a thumbs up, check
out the website, and follow me on Twitter and Facebook!

100 thoughts on “LED Basics

  1. Connected a green led from a local source directly on an Arduino Uno and all was good for the test, but won't take the risk

  2. 👨‍💻💭when i get a LED i mark the pos with red texta 🙂 handy when i test a battery etc 👍 Do not resist the dark side 🤪👀🕺👍

  3. There is a mistake with the explanation of the polarity, the electrons actually flow from the negative to the positive

  4. so if you were running, say, a bunch of LEDs in series, do you need a resistor for every LED or just one resistor for all of them?

  5. I love the brain. When the LED fried at 3:50 i smelled the smell of burned LED's.
    Good and short video, very precise.

  6. You explain it so well for the layman. Awesome! I only wish I could explain it so simply and be interesting at the same time.

  7. I did cause i thought that resistor are just a waste of time and when it did pop i could not even find the top of it

  8. Here is some interesting and useful information. For about 80% of what you need light for at night, or in the dark, the light from one single LED, with the correct and proper voltage applied, will be enough.
    I say this from YEARS of practical experience as I have lived off grid for over nine years now. This single white LED light will use less than one tenth of a Watt of electrical power. One single white LED is then THE most efficient light source on planet Earth. It is enough light to read a book and do nearly all tasks. It is easily enough light to light up a room so you can walk safely in a room in the dark.

    For living off grid, and very likely in the future, this amazing efficiency of energy use will be VERY useful.
    It is hard to imagine that any light source could be more efficient.
    Notice that I said 'with the correct and proper voltage applied' . With the correct and proper voltage applied you will also get that 10,000 hours of life. VERY unfortunately, most LEDs are over-driven, that is, they have too much voltage applied. Most of the cheap multiple LED flashlights take advantage of the fact that most batteries can only supply so much current. However, if one LED burns out, the rest will start getting more current and they in turn will burn out in quick succession.

    In this video the use of resistors is suggested.

    IMHO, it is MUCH better to use voltage and current regulating circuits. There are very small and inexpensive ones available.

    Well, that is my small bit of information. I hope it was interesting and that this information will also be useful to many people.

    Best Regards, Blu Crystl

  9. Thank for the video.
    Basic information is the place to start with. Looking forward to more videos from you.

  10. How is slow color changing RGB LED designed? Can it be programmed to flash much slower so that each cycle would last minutes or so? Why manufacturers consistently make the same duration RGB LED 5mm bulbs that don't even cycle correctly.

  11. It's actually very simple. If you know your LED"s and resistors, you need NEVER do without light. You won't have your PC and all the necessities of life, BUT, you will at least have light. After the Super Outbreak of 4/27/11, our kids learned the positives of actually reading a REAL book! We simply used our rechargeable yard lights for lighting our home during the evening. The next morning, we put them outside to recharge. But you can create your own light sources with LED's and resistors, along with a charge source. You will NEVER be without a light source. Simple. Just use the brain that you have.

  12. Looks like led's work more off voltage with mini-milli-amps where the other lights rely on more amps effecting the watts so heavier gauge wire is needed, if leds were invented at the same time imagine how more advanced we could have been a lot of energy(physical and mental) went into lighting up to now, enormous amounts of wattage produced

  13. The last time I used LEDs for a project (yearzn years), they were all rated for 5V.
     3 x 1.5V batteries worked to light them, too. Then a project came up at work that needed LEDs, and in talking to the guy installing the lights in my design, found out they were all 3V! When did that change come about? Are 5V still made?

  14. Thumbs down are those people that try to run a 220v A/C in a 110v socket by cutting the plug off and installing a 2 prong plug. Believe or not I saw one at Home Depot that was returned. School much?

  15. 1:53 – "Conventional current" – WTF ?? Current flows from negative to positive so the flow of electrons enters the Cathode – not the Anode !

  16. I just repaired an LED magnifying lamp. Apparently, there were many LEDs that were burnt out or simply tired. The circuit is 16 x 6 LED strings in parallel to an 18 VDC supply. Half the strings were either flashing or simply not on. Instead of trying to discover which LEDs were bad, I simply replaced an entire string. The new LED's are much brighter than the old ones. I may just replace all of them.

  17. So do electrons flow from the positive circuit, through the anode to the cathode and down the negative once the connection is established?

  18. I'm looking to install 7 led 0603 into a gundam model kit build. And power them with a USB. I'm a little lost on how to do it. I read I need a 100omh resistor. Any help would be appreciated.

  19. So can a LED work with a 220VDC source and a current limiter set to 30mA?
    The voltage does not matter as long as its above the Vf right?

  20. At least I learned a positive and negative on an LED before I started a project. It would have been nice if the supplier had indicated this in their instructions.

  21. So far this is the best and most concise I have found on the subject. I am a woodworker trying to incorporate some LED lighting into some of my power tools like all my routers, mitre saw and a few others so I am trying to understand how the basics work in order to incorporate an integrated LED driver directly into the tools' body to run some LEDs at directly at the cut. This has helped immensely along with some of your other videos and been an instant subscription.
    Thank you.

  22. I am trying to figure out why the headlamps I got as a free gift at Harbor Freight stop working. They are the kind of headlamps that you wear on your head. I put new batteries in them but that does not help. So I think there is something else that is the problem. I got like 5 or 6 of these headlamps and they are great when they work, and so I just want to fix them so they keep working. Anyone got any suggestions?

  23. In-line current limiting resistors are needed, as well as secret magic fairy dust; that's what make them really light uP! 😎

  24. years ago when blue LEDs first came out, they were not only very expensive ($4 or $5 apiece)
    but also hard to get. one day i'm in 7-11 and i notice a colorful box of cigarette lighters there to

    temp an impulse purchase while you wait for checkout at the register. The lighters have clear

    cases so you can see the fuel, batteries… and 3 LEDs. I pick one up and flick the spark wheel,

    and along with the flame, 3 beautiful blue LEDs light up in a flashing pattern. HOLY HELL!

    3 BLUE LEDs!! The lighters were $1.49 each, and i bought the entire box!

    i always wondered how the lighter people were able to make any money on that deal.

    they must've bought the LEDs a million at a time or something. Interestingly, i never saw those

    LED lighters available at that 7-11 ever again.

  25. Why could've the 100-led line lost brightness all of a sudden?
    Worked fine for several days though …..
    In a blink affected all the line.
    It still goes on but with around 10% of what it used to light.

    Looking forward to your comments.
    Cheers

  26. The cathode of a device is indicated by the letter "K" not "C". The letter "C" is used to indicate a collector. See IEEE 315 Clause 8.4

  27. As the manager of a commercial building I’ve found the lifespan of these products is far shorter than advertised. The failures are not in the LED itself, but rather the drivers. (Transformers). We’ve experienced many premature failures on various fixtures, and replacing the entire unit is usually more cost effective than installing a replacement driver, if available. Of course if we would stop importing substandard crap from China we’d be so much better off in many ways!

  28. LED light is too harsh on the eye's, in my opinion…In the work place, they make you look down, instead of ahead…Or is that the purpose…

  29. why they call it anode and cathode……why they just call it positive and negative……or this naming have an other use……plz tell me

  30. Those little flat 3v coin battery's should work fine right? I want to make LED Stickers for bottles during some party's but want it as cheap as possible

  31. Hey Afrotechmods..
    Noob question here.
    If a 9v battery, as in your example, needs only 3v to run one LED, could I safely wire in 2 more lights into the same circuit?

    Thanks,

    d

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