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!