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 and this process is very inefficient less than 5% of the energy going into the bulb gets turned into light and 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 electro luminescence 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're 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 three important things that 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 an 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 the conventional current will flow out from so you'll connect your negative side of your power source to the cathode for standard five millimeter 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 while 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 and the LED lights up as expected if you get the polarity wrong in your circuit don't worry for low voltage projects the backwards LED blocks current from flowing and it just doesn't turn on okay 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 zero 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's a little different and here's 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 30 milliamps 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 LEDs 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 100ml apps but in general the standard five millimeter LEDs that you're going to be playing with at home are rated for 20 milliamps so what do you do if you want to limit current and you 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
also if you look carefully you'll see that one side of the case has been while 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 and the LED lights up as expected if you get the polarity wrong in your circuit don't worry for low voltage projects the backwards LED blocks current from flowing and it just doesn't turn on okay 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 zero 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's a little different and here's 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 30 milliamps 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 LEDs 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 100ml apps but in general the standard five millimeter LEDs that you're going to be playing with at home are rated for 20 milliamps so what do you do if you want to limit current and you 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
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