How do LEDs work?

The Nobel-prize winning physics of.... reading lights.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, I have a question about Noble prices. Well,
you know they aren't awarded until much later this year
or so, don't stay up late and wait by your phone. Really,
they don't give one for podcasts. No, and they also
don't give a banana prize. Well, my question is about
the Physics Nobel Prize. Well, I'm not staying up late
and waiting by the phone either. Well, my question is
whether it's given to some discovery that is deep or

(00:30):
a discovery that's useful to humanity. Why does it have
to be one or the other. Isn't deep knowledge also useful?
Have you found new trinos to be useful to humanity?
Not yet? Actually, I'm still waiting for aliens to teach
us how to use new trinos to get a safe tan. Yeah,
don't wait by the phone for that. Sweden call me, Jupiter,
call me? What does that even mean? If they're Aliens

(00:52):
and Jupiter? I want the Jovia Noble Prize for Best
Podcast Sidekick. You're not the sidekick. I'm what what I am?

(01:14):
John make cartoon is and the creator of PhD comments
I'm Daniel. I'm a particle physicist, and until a moment ago,
I thought I was the sidekick on this podcast, and
so welcome to our podcast, the award winning science and
physics podcast called Daniel and Jorge Explained the Universe. Remind
me which award we won. We won the award for
having no awards yet, the award for best podcast that

(01:37):
features only two sidekicks. We're sidekicking it here on our podcast.
But yeah, it's our podcast about physics and science and
astronomy and the universe and everything in between. Our podcast
in which we share with you the gorgeous, amazing mysteries
of the universe. We take you on a mental tour
to all the crazy stuff that's out there, that's in here,
the tiny stuff, the huge stuff, and we explain it

(02:00):
all to you in a way that we hope also
makes you chuckle, yeah, because you know, we hope to
open up your mind to the amazing and incredible things
that are happening right now and the far reaches of
the universe and the far corners of the Solar System.
But we also kind of want to open your eyes
to see you all of the amazing signs that's happening
all around you right now. Because one of the most
amazing things about physics is that the same laws of

(02:22):
physics operate on black holes and nebula and neutron stars
and you and me and everything in our world. This
is one of the most earth shattering revelations of physics
in the last few hundred years, that the physics of
the cosmos and the physics of the every day are
the same physics, which means that we can discover the
secrets of the universe just by doing experiments in our laboratory. Yeah,

(02:44):
it's all the same being trapped in a black hole
or being trapped in your apartment for an indefinite amount
of time. It's all the same. You can do physics anywhere.
They're crushing in different ways. But it also means that
we can look around us and find amazing crazy stuff
that reveals the grits of the universe. Like quantum mechanics
was not discovered inside a black hole. It was found

(03:05):
just by shooting photons that weird kinds of metal. And
so today we'll be talking about an invention. Dad, I
would argue maybe is one of the most commonplace or
most prevalent technologies out there in human technology human kind. Right,
are you talking about the wheel fire the hoverboard, and
I was hoping for the hoverboard. Hasn't had that happened yet, Daniel, No,

(03:26):
it is not. But I'm sure somebody accidentally ordered a
hoverboard on Amazon and got something else. You know. Well,
it's a technology that I think basically almost every human
looks at on a daily basis, maybe even an hourly basis.
Now you have me at the edge of my seat.
What are we talking about today? What do you mean?
I thought you knew what we were talking about today.
I'm the sidekick here. Remember you're in charge. Oh I see,

(03:47):
I see. Well, it's in our phones, you know, everyone
looks at their phone every couple of minutes. It's on
our computer screens and our televisions, which I'm sure a
lot of people are watching a lot of these days.
So it illuminates everything you're talking about. My sheer genius, right,
my brilliance about Netflix. I'm just kidding. Well, it's I
just figured out it's on the title of our podcast.

(04:07):
So I'm guessing that people will already know by the
time they click that's right. I hope they haven't been misled.
That's right. We'll lead him to the light. That's right,
So to have the podcast, we'll be talking about l
E d S. How do elds work, what are the
physics of it? And why did somebody win a Nobel

(04:28):
Prize for inventing a particular color of it? That's right,
We have physics Nobel Prizes for things like understanding quantum
mechanics and figuring out what the basic particles are, or
for you know, an observation of gravitational ways. Things really
reveal the fundamental fabric and nature of the universe. And
then we have Nobel Prizes for the invention of the

(04:49):
blue led blue eled, not the red led. That one
did not win. It was blued, Nobel's favorite color. Not
at all, not at all. And so today we wanted
to dive into, like what are the physics of L
E d S. Is it's really worth a Nobel Prize?
What are the sort of obstacles that they had to
leap over in order to make this thing work? And

(05:10):
what physics did they have to solve along the way.
What does it reveal about the nature of our universe
that we can now make L d's globe blues? So
what do you think about my idea that it's maybe
one of the most prevailing technologies out there, you mean
lights in general, or LED specifically, L E D specifically,
you know, because they're they're basically in every phone, and
there's billions of phones out there, and it's on every

(05:30):
computer screen now in TV screen, most of the TV
screens have them. I would say it's up there along
with a concrete and toilet paper as the current most
important technology. Yeah. You know, people have been stockpiling L
e d s ever since the coronavirus came out, you know,
just in case, yeah, you know, just in case we
run out of lights. I think you're right. Just had
a really big impact on everyday life. You see them

(05:52):
in screens, you see them in lights, you see them
on trucks, you see them everywhere now. Yeah. Yeah, So
it's a pretty important technology that's all around us, that
is hitting our eyeballs all of the time. But as usually,
we were wondering how many people out there know how
L e d s work or what it even stands for.
L E ED. So, as usual, Daniel went out into
the world and ask people if they do how an

(06:12):
LED works. That's right, and these questions actually pre date
the coronavirus pandemic and so these are historical records of
in person interviews back when that was still possible. Really, Oh,
this is an actual on the street. These are from
the archive. We haven't had a chance to pull this
episode out yet. I see. Do you think people's opinions
about l E d S would have changed by now?

(06:33):
While people are spending more time inside under the life
of a deeper relationship with L E d S. Now,
maybe hypnotizes a little bit more since Yeah, well you know,
people are looking at more screens and so they have
hopefully more affection for L D. Yeah. So think about
it for a second. If someone asked you how an
LED works, would you know what to answer. Here's what
people had to say. No, but I just know it's

(06:54):
a better life. Part of me really wants you to
say electricity, but uh, isn't it No, that's fluorescence. Remind
I was gonna say gas, but let's just fluorescence light. Yeah,
I'm going to assume it's due to a residents frequency
within within the LED. I'm not sure. Essentially, it's just

(07:17):
a PM junction. Um one side has holes in side
has an accessible electrons, especially transitions in the state of
the PM junction. Really slight. So yeah, oh shoot, um, honestly,
I don't know. I literally don't know. Kind of yeah, yeah,

(07:40):
I know, um excited Adams, but I forgot like which
Adam like maybe alien They excited to higher state energy
state and wave falls generated energy. But yeah, that's kind
of isn't that. Florescen no similar, but fluorescence like much

(08:04):
weaker energy. So what do you think of these responses?
Pretty good? I feel like they fall in live with
how I think about l d S, which is that
I don't know much about him. Yeah, I was a
little surprised. Some people had no idea. Some people thought
they understood it, but we're actually talking about a completely
different type of light generation that's fluorescence. People got them
confused with fluorescent, Like yeah, yeah, In turns out there's

(08:25):
lots of different ways to make light. You know, you
incandescent light, we have fluorescent lights, and then we have
led lights, and they all operate on really different physical principles. Yeah,
because maybe maybe people have got them confused, because I
feel like fluorescent lights, I know, they've been around for
a long time, you know, like neon signs and things
like that, and fluorescent bulbs, but they sort of made
it into people's homes more recently, but then right away

(08:47):
elid sort of came about and then totally replaced them. Yeah, well,
fluorescent lights have been around for quite a long time,
but yeah, they didn't make it into people's homes until
recently with the compact fluorescence. But there's actually sort of
a fascinating legal drama aout florescent lights because they were
first developed pretty soon after incandescent lights, but then General
Electric bought up all the patents and prevented anybody from

(09:08):
developing them or using them, and basically kept fluorescent lights
out of the market for decades just because they also
owned the patents for incandescent lights. So it's sort of
a legal political drama that we probably won't even get
into today. They're like fluorescence that that works with gas,
it's not electric. It's on brand with us, so we'll
just sit in it. Yeah, they just sort of bought
it up and sat on it as a dangerous technology

(09:29):
that they thought would sort of endanger their business. Well,
let's get into how LEDs work, but first let's maybe
talk about how some of the other lights that people
are familiar with work. So take us back, Daniel, how
does it torch work. You know, that's a really awesome
question actually, like what is fire and how does it work?
And I want to do a whole podcast episode, Um,

(09:50):
what is fire and what is the thing you're seeing
that's glowing? And remember it's it's gonna be totally lit.
M We're gonna brighten your life with that one. And
remember on our live streams, somebody asked about that whether
fire can have a shadow, which is a totally awesome question.
But I think the first light that we should talk
about is incandescent lights. And these are the ones that
Edison invented, you know, the ones that people have had

(10:11):
in their homes until very recently. It has a little
filament in it that glows and eventually it breaks, right. Yeah,
basically what people think of when they think of a
light bulb, like a round thing with a little wire
through the middle. Yeah, that's your classic light bulb. And
all the technologies that we're gonna talk about today operate
under the same essential goal, which is turned electricity into photons.

(10:32):
Do you think when Edison had the idea for the
light bulb, do you think he had a light bulb
over his head? Like, was that the only time in
history when like somebody was actually thinking of a light bulb,
when they had an idea. Yeah, that's where it comes from, right,
that was the first great idea, That was the first
idea worthy of having a light bulb over your head. Technically,
that's true. Yeah, And so the idea for incandescent lights

(10:54):
is to find some material where you can deposit the
energy from your electrons and it will give off light.
All right, So every one of these strategies you want
to turn fast moving electrons into shooting off photon photons
to the surrounding areas. Okay, so how do incandescent lights work?
How do light bulbs work? Regularly? The amazing thing about
light bulbs that people probably don't understand is that they

(11:16):
glow even when they're off. What. Yeah, everything glows. It's
called black body radiation. Everything in the universe gives off photons,
gives off radiation, even if it's totally black, even if
it's a black hole, daddy. Well, technically, yes, black holes
do give up a radiation all right, Yeah, that's true. Correct,
Even black holes have a temperature. Right, Everything in the

(11:37):
universe that's not an absolute zero glows at some spectrum. Now,
usually you don't see it because it's invisible. It glows
very very very long wavelengths, very low frequencies, and so
you don't see it. So but this is why, for example,
you know infrared telescopes like the James web Space telescope
that looks for infrared light. It sees a lot out

(12:00):
of noise that you don't even see and have to
keep it cold a like negative fifty degrees or whatever.
So everything in the universe is already glow, but it's
not so useful, right, What you want is something that
glows with light that you can see a lot. Right. Oh,
I see black body radiation is in the infrared. It's
much lower than the infrared. Yet most black body radiation,
like the cosmic Marcrowave background radiation, is black body radiation

(12:23):
from that initial plasma of the universe. And is it
like you know, three degrees kelvin. It's a very very
long wavelength. But what about something that's at zero degreek kelvin,
like absolute zero? Would that still glow? You know, something
that absolute zero can't glow. But there is nothing in
the universe at absolute zero. So if you're like at
point oh one degrees kelvin, from absolute zero, you would

(12:45):
be glowing a little bit exactly. And that's why the
black hole stuff is actually quite fascinating because when Stephen
Hawking developed his ideas of black holes having a temperature,
that automatically suggests that black holes should radiate, because like
everything else that has a temperature, should radiat And that's
why Hawkings results are sort of black hole thermo dynamics,
because he's thinking about the temperature of black holes and

(13:06):
how that connects to how they radiate. All right, so
everything glows into infrared, So how do we get things
to glow in the in the visible light the white
light spectrum. Yes, so the spectrum in which you glow
depends on your temperature. So really cold stuff glows in
the infrared. If you heat something up, then its emissions
move into the visible spectrum. So you want to make
your filament glow in the visible light instead of in

(13:27):
the infrared light. Than what you do is you make
it hot, hotter and hotter. It turns the light from
it not just glows more, but it changes color. It
changes color. And that's why for example, you heat up
metal right and you see it glows blue, it glows red,
It glows white, for example, and the temperature of the
metal determines the frequency at which it's glowing, right, Like
white hot and red hot are different temperatures of metal R.

(13:50):
And so this is a basic principle. And what's going
on in the physics sense, like what's going on with
the electrons on the atoms, why is it changing color?
And how is it giving off the light. So it's
always a good idea to try to think about stuff microscopically.
And that's not just because I'm a particle physicist that
I think we should always be thinking about the tiny stuff.
I think it really does lead to some inside And
so what's happening microscopically when you heat something up is

(14:12):
that the electrons inside of the particles inside it have
more ways to move. They're wiggling more, they're bouncing more.
So there's just a lot more energy there. Now. The
way something glows is when something moves from a higher
energy level to a lower energy level. I mean, like
the atoms in a decay or sort of degrade a
little bit or chill out. And when they do that,
they admit a hotel. Yeah, they're excited. They have some

(14:34):
energy stored in them, and that energy comes from you know,
whatever you did to heat up this material. Right, Heat
means internal energy stored in the motion of these objects,
and we had a whole podcast about what temperature means
and it turns out to be very confusing and amazing,
like everything else in the universe. But the way to
think about microscopically is that these atoms are excited. Either

(14:55):
the electrons that are whizzing around them have gone up
one ladder in the energy level, or two ladders or
three ladders, or maybe they're vibrating in new ways or
rotating in new ways. These are all ways that they
can store energy. The electrons are that are the atoms.
The electrons can move up energy levels, but the atoms
also they can vibrate. Remember a lot of these are
in bonds, right. Metals are not just free floating gases.

(15:16):
These lattices of things tied together and they're like you
can imagine little springs between them, and then you can
imagine those things vibrating and vibrating in different ways. They
have different modes, all right. So they're excited and so
they they're giving off energy and then they relax. Because
things in the universe don't like to be excited. They
like to spread out their energy, and that's why things
emit energy because entropy, right, energy in the universe tends

(15:38):
to diffuse, and so if you have it concentrated in
one little mode, like one little electron has jumped up
three energy levels, it will decay. You'll give that energy off.
And the way it does that is by shooting off
a photon. And so the more you heat up something up,
the more you make all the atoms more excited, the
more you know photons that are going to come off
of this excitement exactly, and then the higher the energy

(15:59):
of those gaps, So an electron can get pushed up
several levels up that ladder, and then it can jump
down five levels, and so then the photon has more energy,
which corresponds to a higher frequency. So that's how, for example,
hot objects can emit in the visible spectrum instead of
just at the very very low energy levels. So the
light that they emit has more energy, which is what

(16:21):
higher frequency means, which is what visible light means, or
invisible light has more energy per photon than infrared light.
But I think it also has to be certain kinds
of materials, right, like when I boil water, it doesn't
start to blow. I mean it starts to glow in
the infrared, but not in the visible light spectrum. That's
an awesome question. How hot would you have to make

(16:41):
water in order to make it glow? I don't think
answer to that. That's a cool question. But you're right, Yeah,
everything glows at some level, but not everything can be
easily made to glow in the visible because I guess
it will melt or burn or boil, yeah, exactly, something
else will happened to it turn into vapor. And so
that that's how light bulbs work. It's that they have
a little thin wire of metal that you heat up

(17:01):
and then that gives us the light. That's right. And
the way you heat it up is that you send
current through it, right, You send electricity through it. And
most of these metals are resistors, meaning that they are
not perfect conductors. So the electrons as they're trying to
go through the metal are getting bounced into atoms, right,
and those atoms are stealing their energy. And this is
what heats up something when electricity passes through it. Like

(17:24):
you know that block that you used to charge your laptop.
Have you've been charging it for a while, it heats up, right,
that's using. That's inefficient. It's using. It's stealing the electricity
from those electrons in order to heat up that block.
This is how you heat up the filament of tungsten.
As you pass all this electricity through it, that heats
it up and that makes it glow. Yeah, that's a

(17:44):
little wire inside of the traditional light bulb and white tungsten.
Is it a special kind of metal? They can heat
up a lot without melting. Yeah, tungsten just sort of
lasts a long time. But these things are really very
very inefficient. Like it's not a very direct way to
get energy into photons. Right, You're just heating this thing
up and it's glowing somewhat in the visible but not
always invisible, and a lot of the energy is just lost.

(18:07):
A lot of the energy goes into the infrared, which
is useless to us. Yeah, it just goes into making
this thing hot, right, and not all the heat gets
turned into visible light, and so only something like five
of the energy that you put into a light bulb
gets turned into light. Superficient, not super efficient and also
kind of fragile, like you're baking this thing every single time,

(18:30):
So it gets hot and then it gets cold, and
gets hot and then it gets cold, and you know that,
like that creates a lot of mechanical stress, which is
why these filaments, which are already very very thin, don't
last for that long. So your typical incandescent classic light
bulb only works for about a thousand hours. Well, they're
making a comeback, you know, and like hip her restaurants
and stuff, everyone's going for the incandescent bulbs. Yeah. Well,

(18:51):
the positive thing about incandescent bulbs is to have a
very nice glow, Like it feels like sort of a
natural light. You know that the process that produces this
light gives you a spread, right, not just one color.
It's not like a laser beam in your eye. It's
a nice spread of warm white light. And so a
lot of people like that. It's sort of more similar
to sunlight than some of the other technologies we're gonna

(19:12):
talk about, saying, all right, let's get into some of
these other technologies like l d s, like fluorescent light bulbs,
but first let's take a quick break. All right, there,

(19:33):
we're talking about how LEDs work and specifically how lights
work in general, and so we're going down the list
of technologies, and so we talked about incandescent bulbs, which
I'm guessing maybe my kids will never have to know
how they work technically because everything is sort of moved on.
But the next one in the history of light is
the fluorescent light bulb. So you were saying these were
invented out around the same time as the incandescent light bulb,

(19:56):
but they worked on a totally different physics. Yeah, the
physics is different. The idea here is to use excited gas,
and you know, we talked about in the late eighteen
hundreds of people were making vacuum tubes and you know,
passing currents through it and seeing glows, and that's actually
one of the things that lead to the discovery of
the electron, right J. J. Thompson discovered the electron by
playing with these sort of evacuated tubes and seeing how

(20:18):
the gas inside them glows. But then people were playing
with other kinds of things and discovered that if you
pass a current through a tube that has gas in it,
you can make the gas glow. And the physics here
is pretty similar to the physics of incandescent lights, except
that you're making a gas glow. Instead of making like
a piece of metal glow, I see, instead of a
little wire, it's like a tube of gas and you

(20:41):
can excite the electrons in that gas. They go up
an energy level and then they jump back down and
they give off a photon. And I think last time
we talked about these, it was it's sort of related
to lightning the way kind of it's it's almost like
you're creating a little bit of lightning in a bottle. Yeah,
it's lightning in a bottle, and it's a little bit
of plasma, right. You In order to pass electricity through
a gas, you have to turn it into ions. You

(21:03):
have to tear apart the positive and the negative that
usually the gas is made out of and make an
ion channel. And you know this sounds like Star Trek
or whatever, but you're literally making a tube of electrically
charged gas. It's like a gaseous wire sort of cool.
It's like a gas that conducts electricity, right, and so
you're tearing it apart just by creating this electric field

(21:25):
from one side to the other and then passing that
energy through and it excites the gas. It makes the
gas like the atoms of the gas inside are now
giving off there like absorbing these electrons that are going through,
and then they give him off as photon. That's right.
The microphysics of what's happening is that these electrons, the
current that's passing through will sometimes bump into an electron
in the gas atom and bump it up a few

(21:48):
energy levels and then it will fall back down. And
when it does that, it gives off a photon. So
you're turning the kinetic energy of some initial electron into
an excited state of the atomic electron, which then it's
a photon. So that's how you get an energy from
the electron into a photon. And it's kind of a
binary process, right, Like it's hard to dim a fluorescent
light bulb, right, Like a little regular ballb you can

(22:11):
do that, but a fluorescent you know, it's either on
and offer and if it's sort of on the edge,
you'll blink and kind of give you ice cream. That's right.
Because you need to create this plasma, you need to
like ramp it up to a high enough voltage so
that you can create this ion channel and the whole
thing starts up. It's almost like starting up a little
fusion reactor. Inside suddenly it Fluorescent light bulbs are way cool.

(22:32):
They're lightning in a bottle and fusion bombs in a tube. Yeah,
And the cool thing about them is that they're a
lot more efficient doing this with gas. Like a mercury vapor,
which is what's typically used, is something like twenty efficient
instead of like the five percent of your incandescent light bulb.
Where does the other scent efficiency go into heat as well?
But they don't. They don't get as that that's exactly right.

(22:53):
They don't get as hot, which is why they're more efficient. Right,
some more the energy goes into creating light unless of
it goes into like heating up the actual apparatus. So
I think that all makes sense. One interesting facet which
I thought was cool was that the best thing to
use to make this light is mercury vapor because you
don't need really high voltage and it's it's one of
the most efficient ways to do it. But mercury is

(23:15):
like super poisonous, which is which makes it like it's
a bad idea. Also, mercury gives off light, it's not visible,
it gives off ultra violet light. Oh my goodness, poisons
you and gives you cancer at the same time. No,
but that's why a lot of these fluorescent light bulbs
are not clear. They're frosted because the inner side of
the glass contains another material which absorbs the ultra violet light,

(23:41):
uses some of the energy, and then gives off light
in the visible So it's like a two step process.
The mercury vapor gives off UV photons which are then
like stepped down into the visible light by some phosphorescent
coating inside the bowl. It's a lot to it. Yeah,
it's a complicated thing, and you know, you have to
create this plasma. And that's why florescent light bulbs until

(24:01):
recently not as commonly used in the home. They're more
expensive and more complicated, but there are a lot more
efficient instead of five and they work for like ten
thousand hours instead of a thousand hours. And the light
is kind of different too. It's it's wider, generally, it's wider. Yeah,
and it kind of drives me bonkers, Like I don't
like the light from fluorescent light bulbs. It makes me

(24:21):
feel like I'm you know, in a target or in
like an alien autopsy examination room. Target and alien autopsy
that's where your mind goes it's worse worst case scenarios. Well, actually,
now that I think about it, I love to be
in an alien autopsy or target for that, to be honest.
It's just that I don't know why the lighting in

(24:42):
alien autopsy scenes in science fiction is always so terrible,
Like why do they always use the horrible fluorescent flickering lights?
I see, Well, it's just so that the green comes
out of their skin more, you know, makes this there's
green skin seemed lovelier. I see. The aliens agent insisted
that they have it that way, is in their contract. Alright, well,
brown eminem's and fluorescent lights, that's right. And I didn't

(25:11):
think that would make you laugh so much, Daniel. I
don't think aliens are so vain alright, alright, well hopefully not.
But yeah, so that's incandescent and fluorescent lights. And so
let's get into the topic of the podcast, which is
how LED lights work. And these are pretty pretty recent.
I feel like in the last ten years they've become
more popular, and they're also sort of everywhere right there,

(25:32):
in phones, they're in TVs or pretty much every kind
of screen, even on people's watches now have L E
D s and so first of all, Daniel, what is
l ED stand for. It stands for light emitting diode.
Light emitting is obvious, right, giving off light and diode
is this little physical thing that was invented in the
fifties and sixties that's made out of semiconductors. And that's

(25:54):
really the core idea here is that instead of using
a hot little tube of metal or a hot tube
of gas, let's see if we can build this thing
out of semiconductors. And semiconductors are what computer chips are
made out of, right, I mean, that's what computers are
made out of. So this is kind of like they
adapted that technology or they figured out they can also

(26:14):
use it to midlight, they can also use to emdlight.
And you're write, semiconductors are incredible also the basis of transistors,
which is how we build computer chips. One of the
cool things about semiconductors is that we can print them
really Finally, we can construct super tiny circuits that have
really specific semiconductors using lithography, and that's how we make
computer chips so small, and we can make l ED

(26:35):
s really small. But first maybe we should talk about
like what a semiconductor is like, it's not somebody who's
like driving a semi for example, someone who's dead driving
with one eye closed, or conducting an orchestra, but only
half the time, yeah, looking at their phone. And so
to understand semiconductor you have to understand where it falls
sort of between other objects like an insulator and a conductor.

(26:57):
It's basically like a conductor that you can control right,
like it's a resistor, but you can also shut it
off if you give it a different sign sort of. Yeah,
I think if it's sort of like a combination between
an insulator and a conductor, because in an insulator, electrons
cannot jump between atoms, like one atom has its electrons
and the other one has its electrons, and electrons just

(27:17):
stay in their atom. They have a little localized the
neighborhood that they hang out in. But in a conductor,
the electrons flow freely, like they don't necessarily have an assignment.
They don't have like a home address. They just sort
of like move around between atoms. It doesn't take much
energy to go from one atom to the next. There's
no barrier there. It insulates, you can't conduct electricity. Yeah,

(27:38):
so insulators electrons can't jump between atoms, and a conductor,
electrons just flow very easily between atoms. Now in the
semiconductor has both, right, it has there's a flow zone
and a no flow zone. So if you have enough energy,
then you can get up into this conduction band where
you can like float around between the atoms. So high
energy electrons can jump between them, but low energy electrons

(28:01):
are sort of stuck in their atom. So there's like
the cool kids that are running all over the neighborhood
and then the ones where their parents tell them they
have to stay home. They're all mixed together. Yeah, and
there's two different kinds and so based on how much
energy you have, and so that's what we call this
band gap. There's this energy gap. If you're above a
certain energy that you can move around and below that
you can't move around. And so that's what a semiconductor is.

(28:22):
And it's fascinating because it has this band gap. And
as you said, if you excite the electrons, you can
turn into a conductor. And but some of the electrons
they're low enough energy then they're an insulator. So you
get this sort of fine grain control about the electrical flow,
which is what makes it good for building circuits and
all sorts of stuff. But it's it's not a question
of the energy of the electrons, right, It's more of

(28:43):
a question of the kind of the energy of the
medium of the material. Yeah, the material determines sort of
this structure, right. Different kinds of semiconductors have different size
band gaps, but that band gap is the energy of
the electrons that we're talking about. And you can build
all sorts of different kinds of semiconductors. And you can
build semiconductors based on like what material you use, like

(29:04):
the gallium, is it, silicon, is it some combination of
these two. You can build semiconductors that have a bunch
of extra electrons in them, so that's called P type,
like there's a bunch of extra electrons floating around. Or
there's semiconductors that are called N types that have like
empty holes where electrons should go. Yeah, so they're both semiconductors,
and they're both about Usually mean add a silicon, right,

(29:26):
with some sort of metal kind of infused in it. Yeah,
And so you often start with silicon and then you
add little bits of other stuff to make different kinds
and a diode is just an N type semiconductor right
next to a P type semiconductor. And what this means
it's very simple. It just means the electricity can flow
in one direction, and that's what a diode does. So
the P type has a bunch of electrons and the

(29:47):
N type has a bunch of holes for those electrons
to fall into. So the P type one has electrons
floating above this band gap that can move around, etcetera, cetera.
When you put a current over, they just fall into
the holes, and electrons jumping from high energy states to
low energy states is how you emit energy. So when
they do that, they release photons. So a diode is

(30:10):
just P type and N type stuck together. And a
light emitting diode is one where when the electrons fall
in they emit visible light. And it has to be
a special kind of material or is it still just
silicon with some kind of metal in it. It has
to be a special kind of material to get the
right color light. And so that's really the key, that's
the core physics for why blue L E d s

(30:31):
were so fascinating. The first LEDs people invented, this gap
was kind of small sort of hard to make it work.
And so when they fell from P type to N type,
they didn't have that much energy and they emitted mostly
in the infrared. And that for example, the LED that's
in your remote control, the when that controls your TV,
you don't see light coming out of the top of
the remote control because it comes out in a wavelength

(30:53):
you can't see it comes out of infrared light to
talk to your TV. But there's an infrared LED at
the top of your remote control. And those are the
first ones that are invented. Is actually back in the
sixties that they first came out with infrared LEDs, and
then the challenge was coming up with different kinds of
material to negotiate this like P type N type difference.
So you've got a larger gap so you have more

(31:15):
energy when they fell, so you have more energy and
the photons so they could be visible light. Uh So
it's all about the difference between the P and the
N types of materials. Okay, So it sort of depends
more on the N type and the on the size
of the hole. Now the hole is just a hole
for an electron. It depends on the gap between the
P type and the ND type. So you're right, it
depends on the type of material and the size of

(31:38):
this gap. And you're putting this P type of this
N type next to each other, and it's basically how
far they fall, Like, are they just stepping down from
the curb and they go oop and they just give
off a little bit of light or they jumping down
Niagara falls and screaming all the way down and giving
off a lot of energy. Oh, I see the electrons
go from the P type to the N type. They jump, Yeah, yeah,
they jump where they fall, you know, depending on whether

(31:59):
you believe the electro is gonna make decisions. Man, they're
pushed or pull more they're more like pulled, right, Yeah,
they're more like pulled. And so basically an led is
a bunch of electrons screaming. So make time you look
at your phone. Your phone is screaming, screaming photons at
you every time. Yeah, it's not just your brain that's

(32:20):
screaming from your Twitter feed. And the thing that's amazing
about this is that it's solid state, right, Nothing is
moving here. You don't have gas that's bouncing around, you
don't have metal that's heating up and cooling down. It's
just fixed and it's just like electrical circuit, and that
makes it last for a very very long time. It
lasts for like a hundred thousand hours before it finally breaks.

(32:40):
It like trust can scream for as long as you need.
That's what you're saying. That's right. Unfortunately, the life span
of electron it's very very long. It's doomed to a
long life of falling down this gap. I guess my
question is what keeps the light going? Like, once it
falls into the hole, wouldn't it just stay in the hole? Yeah,
it does, wouldn't it fill up all the holes? Well,
you have a current it and so you're pulling these

(33:01):
electrons out of the end type. So the whole thing
is connected to a current. Imagine like a battery powering
the led. It's sending fresh electrons into the p type
and pulling the electrons out of the end type. So
the whole thing is a circuit. It is like a waterfall.
It's like a continual waterfall exactly. It's just like a waterfall.
You're pumping on one side and then they scream on
their way down. It's more like a roller coaster because

(33:21):
of the screaming Yeah, that's right, because then they come
back down and then the card gets pulled over and
then up the rap again and then down and then screen.
Let's not think of it as electron suffering, but electrons
is having a lot of fun, that's right. And you know,
you might wonder why do people go on roller coasters
because they scream the whole time? Well, I guess they
like to scream, and so we can imagine that also

(33:43):
electrons are enjoying this ride. There's thrill seekers and they
seem to be happy to do it because LEDs last
for a hundred thousand hours and it's very very efficient.
Most of the energy that you're sending into this circuit
actually goes into emitting light. It's like more than fee
percent of the energy. That's ten times, ten times more

(34:03):
efficient than incandescent bulb. Yeah, ten times more efficient. And
the challenge is in finding the right gaps you get
the right energy level, so you get the right colors.
And so the first thing was infra red, and then
you know, infra red is the lowest frequency, the longest wavelength,
and then they figured out ways to make them longer
so they were visible and then longer, so you've got red,

(34:24):
You've got green, and then the challenge was blue LEDs. Alright,
let's get into the amazing discovery that was discovering blue
LEDs and why I got the Nobel Prize. But first
let's take a quick break. All right, Daniel, somebody got

(34:52):
a Nobel Prize for discovering the blue led. So what's
so special about blue led? I like the way you
make it sound like they discovered a blue l D Like, well,
I was sweeping up my lab and I found this
thing on the ground. Oh my god, it's a blue LED. Right,
It's just what I was looking for, because that's how
we discover particles, right, you know, like, oh my gosh,
look I found a towel particle, and now I get

(35:12):
a Nobel Prize. I didn't like design it or engineer
it or an invented, right, it should be more like
it as somebody designed inventive. Yeah, somebody invented the blue led,
which is sort of awesome and impressive. So we couldn't
just take a white l ED and put a blue
filter on it. Well, that's the thing. You can't make
white l d s without blue. Right before we had
blue l e d s, we had green, and we

(35:34):
had read and so you couldn't make white l e
d s. That's why blue l d s are so
important because with blue you can make the combination you
need to make white. And nobody wants in their reading
light a green light or a red light. You want
a white l e ED And you couldn't make white
without blue. You need the blue. You need the blue
to make the need the blue to make the white.

(35:55):
And that's why l ds have exploded in applications everywhere
because now they can make essentially any color because we
have the missing blue cool. So tell me what was
so hard about it and what's the physics behind it? Yeah,
and so it's sort of an interesting question, like it
really was an engineering puzzle, Like you just needed to
get the right material. You needed to get the right
material with the right thickness and configure it all correctly

(36:16):
to get blue. And it was tricky to get this
gap to be extra extra large, large enough to make
so that when the electrons go down that roller coaster
they scream for long enough to give you a blue photon.
And you know, it turns out to be something of
a condensed matter and solid state engineering problem and a
couple of Japanese people figured it out. You need some
mixture of gallium nitride with other silicon substrates and then

(36:40):
you can get this blue led. But I guess why
was it so hard? Like when you try to make
electrons jump that much, it would burn out or they
just wouldn't do it, or you know, they wouldn't scream
as much as you wanted to. What was the difficulty
in getting this right? It's just in finding one that
would work. You know, most things just didn't have this
large enough gap, and so it's just a finding a

(37:00):
material that had this gap and that also worked. Yeah,
and that also works. I mean, you can make a gap,
but it may not necessarily work to get the electrons
to flow across it, And so we can't necessarily predict
in advance whether something is going to work. So they
sort of had just had to search through lots of
different kinds of materials and try this and try this,
and have inside and inspiration and also just some luck
into making it work. And so that's why I think

(37:21):
it's interesting, like does this deserve a Physics Nobel Prize?
Like there's no new principle discovered here, There's no fundamental
revelation of the nature of the universe or space, time
or history or whatever. It was an engineering step forward,
which a deep respect for the engineering step forward. But
I think the reason it got the Physics Nobel Prize

(37:42):
is because of the huge impact on society. Really, you
guys look down on things that are useful. You're like, well,
you know, I think the original Nobel Prize was supposed
to be about things that shape society, and so I
think Alfred Nobel would probably be it. He pleased. But
more recently a lot of these prizes have been awarded

(38:04):
for like deep but maybe impractical discoveries about the nature
of neutrinos or gravitational waves. I see, that's right. Nobel
was an inventor, right, He wasn't a physicist, he was
an engineering exactly. You guys have co opted our prize exactly.
So in some sense this is like a return to
Nobel's roots, right. It's recognizing something of great import to

(38:25):
society because it has had a huge impact. It was
like the missing piece. There's nothing weird physically about blue.
It's just sort of the highest frequency and therefore the
last for us to put together. I said, so do
you think somebody should have gotten a prize, a Nobel
prize for discovering the Higgs boson, because the people who
wanted wanted for coming up sort of with the Higgs boson,
but the people who discovered it, it was mostly just

(38:47):
sort of engineering. Right. You just described my whole field
as mostly sort of just engineering, which is so many
it fastening the angles because I think you meant that
as a disc but you described as engineering. So I
hold engineering that at the highest esteem. That was actually
trying to pay you a compliment. You were trying to
elevate our field by describing ange. I appreciate that it's

(39:07):
aspiring to be useful. Well, I'm not even sure how
useful it is to discover the Higgs boson. But I
think the great innovation there was definitely having the idea
and finding it. I don't know how many big steps forward,
and me it's a huge effort and technological achievement, But
I don't know that we necessarily created anything new. We
certainly didn't make anything as fascinating and impactful as the

(39:30):
Blue Led. We just sort of confirmed an idea that
it was in people's minds, so we revealed something about
the nature of the universe, but something that sort of
had been suspected to exist already. But okay, so back
to the blue l d. That's important because now you
have blue, and with red and green you can make
white lights. So you can make any kind of color
now that you have blue lads. Yes, exactly, And so

(39:52):
these guys invented it in the nineties and then they
won the No About Prize for it a few years later.
That's how ladies work, and that's why there's important. So
the people who discovered the red ladies and the green
ladies also get a price, or only the one who
waited till the end and procrastinated to discover the missing
color get the prize. I feel like you have another
horse in this race here, your pro procrastination. I built

(40:16):
a whole career on it. Any Yeah, the lesson here
is weight and just sort of put the period at
the end of the sentence and you'll get the prize
for everybody else's work. Yeah, there you go. But in
a way, it's true, right, like the person who discovered
the red and the green one didn't get a prize,
but somehow, like you know, completing the triangle to get
white light made a bigger splash. The person who puts
the capstone on the top of the pyramid, right, is

(40:38):
the one that claims the prize, right, the one who
discovers the mass particles the one who But yeah, so
now we can make white light with LEDs that is
super efficient and also small, really small. Like maybe before
you couldn't make incandescent bulbs small enough for you know,
written and display kinds of screens, but now you can't
because you can can really really small yeah, because we

(41:00):
can print stomic conductor is using these lithography techniques to
be really really super tiny. And you know, we invented
these techniques mostly so we can make transistors really really small,
so we can make computer chips packed with all sorts
of little circuits on them. But we can also use
the same technology to make l E d s and LEDs. Remember,
are not monochromatic. They're not like tiny little lasers. Right,

(41:21):
Lasers shoot exactly one frequency, are very very tight band
and frequency because the photons come from one atomic step.
Ellis are not quite like that. The light they admit
is narrowly focused, doesn't have just a single wave length
or frequency. It's like it is a little bit like
in Contestant, and that it's kind of broad. Yeah. Yeah,
they're broader than lasers, but not as broad as in Contestant.

(41:43):
So that's why there are specific color, but they're not
like a really tight band like lasers. So then when
I turn on the flashlight on my phone and I
see this wide light come off, and that helps me
at night and get around at night, I'm actually seeing
not a white led, but like a whole bunch of red,
blue and green lads mixed together. That's right. And when
you look on your screen and you see white for

(42:04):
the blank page and the word document of the novel
you've been writing for ten years, than what you're really
seeing our red, green and blue blinking, your failure action blinking.
But you know, that's what Newton discovered is that white
light is actually just a mixture of colored lights. There's
no difference, There is no white photon, there's no color
in the spectrum that is white. White light is just
a mixture of red, green, and blue. And so basically

(42:27):
that increased our human level global efficiency for light by
ten times. So now we can be a whole lot
more eco friendly. Yeah, except probably just means we made
a lot more bulbs, so probably using the same amount
of electricity, and now we're just lighting everything up. You know,
I changed all the light bulbs in my house for
l d s and boy, your power bill drops like crazy. Yeah. Well,

(42:50):
do you appreciate it though? For working? Like when you're
drawing something, do you like using natural light or incandescent
light or LED light or does it not make any
difference because you do everything at well, I drive everything
on the computer, so it's all LED power, baby, you know, yeah,
I guess so. All right, Well that's pretty cool. I

(43:10):
have a new respect for blue lads now, and also
liver respy for red and green lads. You know, I
feel like they got the short end of the colored triangle.
They are singing the Nobel Blues, all right, but I think,
you know, it points us to how even a small
discovery in physics or experimental physics can lead to basically
revolution and how we lead our lives and what kinds
of devices we use every day. That's right. Engineering can

(43:33):
change to the world. What can you guys replay that?
Which is one more time? I just want to make
sure that we heard it right. Can you replay it?
Engineering can change to the world. You know, I'm gonna
download it, frame it, frame it on an led frame.
I should send you a little button. You can just
press that and hear me say that. Hag into your

(43:54):
phone and make it your ring tone. All right. Well,
we hope you joined that, and we hope you look
at light in a whole different light. Thanks for tuning in,
See you next time. Thanks for listening, and remember that.

(44:14):
Daniel and Jorge Explain the Universe is a production of
I heart Radio. For more podcast from my heart Radio,
visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows. Yeah,