Daniel and Jorge Explain the UniverseThe Nobel-prize winning physics of.... reading lights.
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Hi.
I'm David Ego from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford, and I've spent my career exploring the three pound universe in our heads.
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Hey, Daniel, I have a question about Nobel prices.
Well, you know they aren't awarded until much later this year, so don't stay up late and wait by your phone.
Oh really, they don't give one for a podcasts.
No, and they also don't give a banana prize.
Well, my question is about the physics Nobel price.
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 a discovery that's you useful to humanity.
Why does it have to be one or the other. Isn't deep knowledge also useful?
Have you found neutrinos to be useful to humanity?
Not yet?
Actually, I'm still waiting for aliens to teach us how to use neutrinos to get a safe tan.
Yeah, don't wait by the phone for that. Sweden, call me, Jupiter, call me what is that? If there are eighties and Jupiter, I want the Jovian Nobel Prize for Best Podcast. Sidekick.
Wait, you're not the sidekick.
I'm decided what I am. Horehea, my cartoonist and the creator of PhD.
Comments, Hi, 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 Explain the Universe.
Remind me which award we.
Won, the award for having no awards yet.
The award for best podcast that 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 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 in 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 science that's happening all around you right now.
Because one of the most amazing things about physics is that the same laws of 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 everyday are the same physics, which means that we can discover the secrets of the universe just by doing experiments in our laboratory.
Yeah, 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 secrets of the universe. Like quantum mechanics was not discovered inside a black hole. It was found just by shooting photons at 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 humankind.
Right, are you talking about the wheel fire?
The hoverboard? I was hoping for the hoverboard. Hasn't that that happened yet, Daniel.
No, it is not, but I'm sure somebody accidentally ordered a hoverboard on Amazon got something else.
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, I see what's on our phones? You know, everyone looks at their phone every couple of minutes. It's on our computer screens, on 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.
Talk about Netflix. I'm just kidding. Well, it's I just figured out it's on the title of our podcast. So I'm guessing that people will already know by the time they click in.
That's right. I hope they haven't been misled.
That's right. We'll lead them to the light.
That's right.
So to that the podcast, we'll be talking about LEDs. How do LEDs work, what are the physics of it? And why did somebody win a Nobel Prize for inventing a particular color of it?
That's right. We have physic Nobel Prizes for things like understanding quantum mechanics and figuring out what the basic particles are, or for you know, an observation of gravitational waves. Things really reveal the fundamental fabric and nature of the universe. And then we have Nobel Prizes for the invention of the blue led.
Blue led, not the red led. That one did not win. No, 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 LED's Is it 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 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 LED's globe blue?
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 LED specifically, you know, because they're basically in every phone, and there's billions of phones out there, and it's on every computer screen, know, in TV screen, most of 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, if people have been stockpiling LEDs ever since the coronavirus came out, you know, just in case they ran out.
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 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 LED's work or what it even stands for LED. So as usual, Daniel went out into the world and ask people if they do how an 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.
Oh 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 LEDs would have changed by now?
While people are spending more time inside under the lights looking at instead of a deeper relationship with LED's.
Name, maybe hypnotizes a little bit more since.
Yeah, well you know, people are looking at more screens and so they have a hopefully more affection for LED.
Yeah. So think about it for a second. If someone asks 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 a better light.
Part of me really wants you to just say electricity, But isn't it. No, that's fluorescence. Never mind, I was going to say gas, but that's just fluorescence the light.
Yeah, I'm going to assume it's due to a resonance frequency within within the LED.
I'm not sure.
Essentially, it's just a PM junction. One side has holes inside has an accessible electrons, and especially transitions in the state of the PM junction really slight.
So yeah, oh, honestly, I don't know.
I literally don't know.
Kind of yeah, yeah, I know excited Adams, but I forgot like which Adam like maybe alien They excited to a higher state energy state and where he falls generates energy. But yeah, that's.
Kind of isn't that Fluorescence?
No similar, but fluorescence is like much weaker energy.
So what do you think of these responses?
Pretty good? I feel like they fall in love with how I think about LEDs, 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 him confused with fluorescent, Like.
Yeah, yeah, it turns out there's lots of different ways to make lights. You know, you have incandescent light, we have fluorescent lights, and then we have LED lights, and they all bread on really different physical principles.
Yeah, 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 LED 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.
Yeah.
But there's actually sort of a fascinating legal drama about fluorescent lights because they were first developed pretty soon after incandescent lights, but then General Electric bought up all the patents and prevented anybody from 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 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 that they thought would sort of danger 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 the 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 on what is fire and what is the thing you're seeing that's glowing and cool? And remember that's it's going to be totally lit. We're going to brighten your life with that one. And remember on our live stream 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 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 going to talk about today operate under the same essential goal, which is turn electricity into photons.
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 is to find some material where you can deposit the energy from your electrons and it'll give off lights. Right, So every one of these strategies you want to turn fast moving electrons into shooting off.
Photons photons to the surrounding areas. Yeah, okay, So how do incandescent lights work? How do light bulbs work?
Regular One the amazing thing about light bulbs that people probably don't understand is that they 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. Dad, Well, technically, yes, black holes do give a radiation, all right, Yeah, no, that's true. I stand correct.
Yes, even black holes have a temperature. Right, Everything in the universe that's not an absolute zero glows at some spectrum. Now, usually you don't see it because it's invisible. It glows it 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 of noise that you don't even see and have to keep it cold at like negative fifty degrees or whatever. So everything in the universe is already glowing, but it's not so useful.
Right.
What you want is something that glows with light that you can see a lot.
Yeah right, Oh, I see. Black body radiation is in the infrared.
It's much lower than the infrared, yet it's most black body radiation, like the cosmic microwave. Background radiation is black body radiation from that initial plasma of the universe, and it's at like, you know, three degrees kelvin. It's a very very long wavelengths.
But what about something that said zero degreek kelvin, like absolute zero, would that still glow?
No, something that absolute zero can't glow. But there is nothing in the universe at absolute zero.
So if you're like at point one degrees kelvin from absolute zero, you would 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, they should radiate. And that's why Hawking's results are sort of black hole thermodynamics, because he's thinking about the temperature of black holes and how that connects to how they radiate.
All Right, so everything glows in the infrared, So how do we get things to glow in the visible light the white light spectrum.
Yeah, 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 it's emissions move into the visible spectrum. So you want to make your filament glow in the visible light instead of in 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, right. And so this is a basic principle.
And what's going on in the physics sense, like what's going on with the electrons and 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 insight. And so what's happening microscopically when you heat something up is that the electrons inside it, the particles inside it, have more ways to move. They're wiggling more, and 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 it decay or sort of degrade a little bit or chill out. And when they do that, they emit a photon.
Yeah, they're excited. They have some 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 it microscopically is that these atoms are excited. Either 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 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. There are 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 of energy.
And then they relax because things 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 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 excitment.
Exactly, and then the higher the energy 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 higher frequency means, which is what visible light means, or in visible light has more energy per photon than infrared light.
But I think it also has to be certain kind of materials, right, Like when I boil water, it doesn't start to glow. I mean it starts to glow in the infrared, but not in the visible light.
Spiker, that's an awesome question. How hot would you have to make water in order to make it glow? I don't know the 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.
Business because I guess it'll melt or burn or boil.
Yeah, exactly, something else will happen to it turn into vapor.
And so that's how light bulbs work. It's that they have a little thin wire of metal that you heat up 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 you know that block that you use to charge your laptop. Have you've been charging it for a while, it heats up, right, that's using, that's in efficient, it's using. It's stealing the electricity from those electrons in order to heat up that blot. This is how you heat up the filament of tungsten, is you pass all this electricity through it. That heats it up and that makes it glow.
Yeah, that's a little wire inside of the traditional light bulb and white tungsten. Is it a special kind of metal that 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 in the visible, and a lot of the energy is just lost.
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 percent of the energy that you put into a light bulb gets turned into light.
Wow.
Not super efficient.
Not super efficient, and also kind of fragile, like you're baking this thing every single time. So it gets hot and then it gets cold, and it 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 restaurants and stuff, everyone's going for the incandescent bulbs. Yeah.
Well, the positive thing about incandescent bulbs is to have a very nice glow, like it feels like sort of a natural light. You know. 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, a 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 going to talk about seeing.
All right, let's get into some of these other technologies like LEDs, like fluorescent light bulbs, But first let's take a quick break.
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Right there, we're talking about how LEDs work and specifically how lights work in general. 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 has 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 at around the same time as the incandescent light bulb, but they worked on a totally different physical.
Yeah, the physics is different. The idea here is to use ex gas and you know we talked about in the late eighteen hundreds, people were making vacuum tubes and you know, passing currents through it and seeing glows. And that's actually one of the things that led to the discovery of the electron, right. J. J. Thompson discovered the electron by playing with these sort of evacuated tubes and seeing how 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.
Yeah, and you 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 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. In order to pass electric city through a gas, you have to turn it into ions. You 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 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. They're like absorbing these electrons that are going through and then they give them 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 energy levels, and then it'll 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 emits a photon. So that's how you get 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 bulb, you can do that, but a fluorescent you know, it's either on and off or and if it's sort of on the edge, you'll blink and kind of give you ice stream.
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. Oh my god, it's sort of awesome.
Yeah, Suddenly, florescent light bulbs are way cooler. They're lightning in a bottle and fusion bombs two.
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 percent efficient instead of like the five percent of your incandescent light bulb.
Where does the other seventy eight percent efficiency go into heat as well? But they don't get us.
Well, that's exactly right. They don't get as hot, which is why they're more efficient. Right, So more the energy goes into creating light and less 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 like super poisonous, 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. Yeah, 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, 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.
So a lot to it.
Yeah, it's a complicated thing, and you know, you have to create this plasma. And that's why fluorescent light bulb until recently not as commonly used in the home. They're more expensive and more complicated, but they're a lot more efficient, like twenty percent instead of five percent, and they work for like ten thousand hours instead of a thousand hours.
And the light is kind of different too. It's wier generally, it's wider, Yeah, and it kind of drives me bunkers, Like I don't like the light from fluorescent light bulbs. It makes me feel like I'm, you know, in a target or in like an alien autopsy examination room. Oh lot, target and alien autopsy. That's where your mind goes. It's worse worse case scenarios.
Well, actually, now that I think about it, I'd love to be in an alien autopsy.
Yeah, or target for that, to be honest.
It's just that I don't know why the lighting in alien autopsy scenes in science fiction is always so terrible, like, what are they always use the horrible florists and flickering lights?
I see, Well, it's just so that the green comes out of their skin more. You know, it makes this there's green skin seem lovelier.
I see. The alien's agent insisted that they have it that way, is in their contract. All right, Well, brown m and m's and fluorescent lights pace.
Right, that's right and able. I didn't think that would make you laugh so much, Daniel.
I don't think aliens are so vain, all right.
All right, 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 recent. I feel like in the last ten years they've become more popular. And they're also sort of everywhere, right, They're in phones, they're in TVs or pretty much every kind of screen, even on people's watches. Now I have LEDs, and so, first of all, Daniel, what does LED stand for.
It sends 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 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 use it to midlight.
They can also use it to emit light, and you're right, 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 finely. We can construct super tiny circuits that have really specific semiconductors using lithography, and that's how we make computer chips so small. We can make LEDs 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 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.
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 signal.
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 stay in there atom. They have a little localized little 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 there.
Yeah, So insulators electrons can't jump between atoms, and a conductor electrons just flow very easily between atoms. Now, in a 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 lowergy electrons 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, 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. So that's what a semiconductor is. And it's fascinating because it has this band gap. And as you said, if you excite the electrons, you can turn it into a conductor. 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 not a question of the energy of the electrons, right, It's more of 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 semic conductors, and you can build conductors based on what material you use, like a 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 it'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 of the usually mean ad a silicon, right, 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 is very simple. It just means the electricity can flow in one direction. That's what a diode does. So the P type has a bunch of electrons and the 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. They can move around, et cetera, et cetera. When you put a current over it, 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 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 LEDs were so fascinating. The first LED's 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 for example, the LED that's in your remote control, the one 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 you can't see. It comes out as infrared light to talk to your TV, but there's an infrared LED at the top of your remote control. Those are the first ones they're invented. It's 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 energy when they fell, so you have more energy in the photons so they could be visible light.
Oh, so it's all about the difference between the P and the N types of materials. Yes, okay, so it sort of depends more on the N type and 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 end type. So you're right, it depends on the type of material and the size of this gap. And you're putting this P type and this ND 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 are 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, I see, Yeah, they jump where they fall. You know, depending on whether you believe the electrons can make decisions, they're pushed or pull They're more like pulled, right.
Yeah, they're more like pulled. And so basically an LED is a bunch of electrons screaming.
So great, next time you look at your phone, your phone is screaming the area photons at you every time. Yeah, it's not just your brain that's 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 an electrical circuit, and that makes it last for a very very long time. It lasts for like one hundred thousand hours before it finally breaks.
Electrons can scream for as long as you need them to. That's what you're saying.
That's right. Unfortunately, the lifespan of electron it is 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, right, and so you're pulling the 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 time. 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 of the screaming.
I see, Yeah, that's right. Then they go bent down and then the cart gets pulled over and then up the wrap again and then down and then screen. Let's not think of it as electrons 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 electrons are enjoying this ride.
That's where you go.
There's thrill seekers, and they seem to be happy to do it. Because LED's last for one 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. Yeah, it's like more than fifty percent of the energy.
Wow, that's ten times, ten times more efficient than the incandescent bule.
Yeah, ten times more efficient. And the challenge is in finding the right gaps you get the right energy levels, so you get the right colors. And so the first thing was infrared, and then you know, infrared 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 got red, you got green, And then the challenge was blue LEDs.
Dumb.
All right, let's get into the amazing discovery that was discovering blue LEDs and why it got the Nobel Prize. But first, let's take a quick break.
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Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford, and I've spent my career exploring the three pound universe in our heads. We're looking at a whole new series of episodes this season to understand why and how our lives looked way they do. Why does your memory drift so much? Why is it so hard to keep a secret, When should you not trust your intuition? Why do brains so easily fall for magic tricks? And why do they love conspiracy theories? I'm hitting these questions and hundreds more because the more we know about what's running under the hood, better we can steer our lives. Join me weekly to explore the relationship between your brain and your life by digging into unexpected questions. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
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All right, Daniel, somebody got a Noble 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 led. 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, we're like, oh my gosh, look I found a tau particle and now I get a Nobel Prize. I didn't like design it or engineer it or invent it.
Right, it should be more like somebody designed blue d invented.
Yeah, somebody invented the blue led which is sort of awesome and impressive.
So we couldn't just take a white LED and put a blue filter on it.
Well, that's the thing. You can't make white LEDs without blue. Right before we had blue LEDs, we had green and we had red, and so you couldn't make white LEDs. That's why blue LEDs 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 LED and you couldn't make white without blue.
Oh, you need the blue. You need the blue to make the blue.
To make the white. And that's why LEDs 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 to get blue. And it's 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 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 was just in finding one that would work. You know, most things just didn't have this large enough gap, and so it's just about finding a material that had this gap.
And that also worked.
Yeah, that also worked.
I mean you can make a gap, but it it may not necessarily work.
Yeah, to get the electrons to flow across it. And so we can't necessarily predict in advance something's 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 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 hey, deep respect for the engineering step forward. But I think the reason it got the Physics Nobel Prize 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 pretty pleased. But more recently, a lot of these prizes have been awarded for like deep but maybe impractical discoveries about the nature of neutrinos or gravitational with.
Oh, that's right, Nobel was an inventor, right, he wasn't a physicist.
He was an engineer, exactly. You guys have co opted our prize exactly. So in some sense, this is like a return to Nobel's roots, Right, is recognizing something of great import to society because it has had a huge impact. Right, 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.
Oh, 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 want it for coming up sort of with the Higgs boson, But the people who discovered it it was mostly just sort of engineering. Right.
You just described my whole field as mostly sort of just engineering, which is so many at fastening the angles because I think you meant that as a diss but you described it as engineering.
So no, I hold engineering that the highest esteemed I know. I was actually trying to pay you a compliments.
You were trying to elevate our field by describing as engineering.
DS.
I appreciate that.
It's aspiring to be useful.
Well, I'm not even sure how useful it is. Just over the Higgs boson. But I think the great innovation there was definitely in having the idea and finding it. I don't know how many big steps forward. I mean, 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 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 led that's important because now you have blue, and with red and green you can make white light, so you can make any kind of color. Yes, now that you have blue LEDs.
Yes, exactly. And so these guys invented it in the nineties and then they won the Nobel Prize for it a few years later. That's how LED's work, and that's why there's on boardant.
So that the people who discovered the red LEDs and the green LEDs also get a prize, 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.
Yeah, I've built a whole career on it. Anyway.
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 will 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.
Yeah, the person who puts the capstone on the top of the pyramid, right, is the one that claims the prize, right.
The one who discovers the mass particle is 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 at display kinds of screens, but now you can because LEDs, you can make them really really small.
Yeah, because we can print sema conductors using these lithography techniques to be really really super tiny. And you know, we'd 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 LEDs. And LEDs, remember, are not monochromatic. They're not like tiny little lasers. Right. Lasers shoot exactly one frequency or very very tight band or frequency because the photons come from one atomic step. Las are not quite like that. The light they emit is narrowly focused.
It doesn't have just a single wave length or frequency. It's like it is a little bit like incandescent that it's kind of broad.
Yeah. Yeah, they're broader than lasers, but not as broad as incandescent. So that's why there are specific color. But they're not like a really tight band like lasers.
Okay, so then when I turn on the flashlight on my phone and I see this white 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 LEDs mixed together.
That's right. And when you look on your screen and you see white for the blank page and the word document of the novel you've been writing for ten years, than what you're really seeing, are red, green, and blue blinking?
Your failure actually 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.
Wow.
And so basically 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 out of electricity, and now we're just lighting everything up.
No, I changed all the light bulbs in my house for LEDs in boy, your power build drops like crazy.
Yeah. Well 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 two am?
Well, I draw 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 have a new respect for blue LEDs now and also a little respect for red and green LEDs 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 as to how even a small discovering physics or experimental physics can lead to basically a revolution in how we lead our lives and what kinds of devices we use every day.
That's right. Engineering can change the world.
What Yeah, 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 the world.
I'm going to 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 you want.
To hag into your phone and make it your ringtone tone? All right? Well, we hope you enjoyed 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 Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeart Radio, visit the iheartradiopapp, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth. You're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford and I've spent my career exploring the three pound universe in our heads.
Join me weekly to explore the relationship between your brain and your life.
Because the more we know about what's running under the hood, better we can steer our lives. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
Parents looking for a screen free, fun and engaging way to teach your kids the Bible as a mom. I was looking for the same thing, so I created Kids' Bible Stories podcast. Thousands of families are raving about it, and kids actually request to listen. With captivating sound effects, voices, and an apply section at the end to spark meaningful conversations, it's a hit with both kids and parents. Listen to Kids Bible Story's podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
