Cool! The liquid nitrogen is causing the semiconductors band gap to shrink which effects the color of the LED via photon energy and shortening wavelength. Warn it up and it returns to normal.
“They’re sciencing hard” - ah yes the phenomenon of cooling materials down and .. expanding? Not quite.
Remember in elementary school, for us it was 3rd grade, a science class demo on how an empty can or bottle can be heated and then dunked into cold water, causing it to rapidly crumple itself up?
Or a metal ring captive behind a metal ball on the end of a shaft but after hitting the ring with a torch for a few moments, it can be slid over the ball?
Cooling down this specific type of LED by such a significant amount from ambient opens the gap, because the material is contracting, enough to where it can emit different wavelength of light.
Theres things that can prevent this too. The driving circuit not permitting adequate current or forward voltage for example.
Room temperature examples of this circuit limitation include cheap toys with Red/Green/Blue LEDs driven by a tiny coin-cell battery.. as the battery voltage drops eventually you’ll only see red and green light.
Further voltage decline will yield only red light as diodes require a certain electrical potential (“forward” voltage) to function and different color photons need different voltages to be emitted. Red light being the flavor of visible light with the longest wavelength and thus the lowest energy
It causes the band gap to widen actually. When temperature drops, vibrations decrease and the crystal lattice contracts slightly, increasing the band gap energy.
That's great info, i'm sure, but i don't see how it answers the question of why "mechanically," the contraction of the lattice increases the band gap energy, and doesn't - say - decrease it.
Because chemical structures use orbitals, which are energy dependent and what influence the energy gaps. If you change the orbitals (changing the structure) you change the gap (the energy needed to go from one place to another), I think.
It bothers me that you grammar Nazis think language is composed of objective rules rather than a way for us to communicate with each other. Changing the E to an A doesn't make it any easier to understand what they were trying to communicate.
Those are two entirely different sentences. Did you give my wife a dollar or did you have sex with her? There's no other way to reasonably interpret that person's comment.
It broadens* larger gaps produce shorter wavelenghts (going from yellow to green, since higher energy is needed to bridge it). It is also known that semiconductors gain resistance with lower temperatures, which is what causes the the higher power here (and therefore different wavelenght), I think.
‘I looked then and saw that his robes, which had seemed white, were not so, but were woven of all colours, and if he moved they shimmered and changed hue so that the eye was bewildered. ‘“I liked white better,” I said. ‘“White!” he sneered. “It serves as a beginning. White cloth may be dyed. The white page can be overwritten; and the white light can be broken.” —LoTR
ironically this answer is fake news. The bandgap increases due to there being less thermal energy. An increased band gap means that the photons that are released will have increased energy and thus a shorter wavelength or a higher frequency.
While true, I'd emphasize that they were nitride compounds. GaAs had been used for quite a bit longer to make red emitters, so the innovation related to the nitride.
What you are witnessing here is a very basic application of physics, neuroscience, quantum mechanics, mechanical engineering, materials science, optics, chemistry, advanced mathematics and probably a bit of thermodynamics.
I figured it out in about 0.3 seconds while casually scrolling, because unlike some people, I understand how the universe works.
The fact that this subreddit is called blackmagicfuckery is, of course, deeply misleading and intellectually offensive to me personally.
Please stop enjoying things incorrectly.
Thank you.”
LED aside, isn't it rather dangerous to get so close to liquid nitrogen gloveless? I know the Leidenfrost effect makes it fall off you if you get splashed, but that's just sitting there and if you dip your finger accidentally it's toast, no?
It will frostbite you pretty hard if you dip it. This is why cooking programmes where you see people using it with no PPE piss me off.
Edit: I admire everyone’s confidence, but note that during my chemistry degree and my early career as an organic chemist, we would not go near dangerous goods, such as liquid nitrogen, without PPE (and, yes, ventilation — it is of course an asphyxiant). It is a Class 2.2 Dangerous Good. If you use Dangerous Goods without risk assessment, and controls such as at the very least PPE, you generally increase the risk of injury.
There are of course contexts in which we all handle DGs day-to-day without PPE; notably filling our cars with petrol (gasoline, a Class 3 Flammable DG). This has other controls incorporated like engineering controls; e.g. designs of the nozzles at the pump, and the filler neck on your tank.
Splashing LN around on MasterChef or having open bowls of it is unwise. I’m fully aware of the Leidenfrost effect, but Leidenfrost won’t stop that stuff blinding you if you splash it in your eyes, or suffocating you (or the next person to enter the room), for example.
Don’t be a panic-merchant, sure — but know that Dangerous Goods, by definition, don’t give a rat’s about how brave, confident or flippant you are.
Yeah it’s perfectly safe if it splashes on your clothes. When I was a hilarious student we used to enjoy putting people’s wooly hats into nitrogen and then moulding them into phallic shapes before putting them back onto somebody’s head.
Unless you have the reflexes of a sloth, you'd naturally yank your hand back way before any permanent damage was done. You'd probably have some 1st degree burns though.
It’s also in a bowl that you can see shake when he hits it with his hand several times. Possible scenario..Does touch the liquid nitrogen, yanks hand back, makes bowl flip, LN goes flying into his face and eyes. This idiot is a Darwin awards candidate.
In semiconductors, the colder the temperature the higher the resistance, and higher the resistance, higher the energy emitted due to the increase in colisions, which translates in a shorter wavelenght.
Hang on a second - so you can modulate temperature to continuously sweep across a good part of the visible spectrum?
LEDs are narrow band emitters - not as sharply tuned as lasers, but close.
If you can change the exact emitted frequency by changing the temperature via something like a thermocouple embedded into the LED... that's pretty big. I think.
Edit: why down vote? Being able to produce spectrally pure light at an arbitrary wavelength is quite valuable.
I'm pretty sure that's not what a thermocouple does lol. Thermocouples are used to measure temperature differences, which induce a voltage in the thermocouple due to the Seebeck effect. This also works in reverse, but the device is called something else: a Peltier cooler. Anyway, I think the reason you're being downvoted is because the idea isn't as practical as you might think. Basically, temperature control is hard. Being able to tune the light to exactly the wavelength you want will be tricky, especially if the environment isn't climate controlled.
Sigh. If you run current across a thermocouple, you induce a temperature difference across the junctions - heating one, and cooling the other, depending on the direction of the current.
This is the peltier effect, and cascade peltier systems can achieve ~ -90c from room temperature
Add in a closed loop control system via an embedded thermistor, modulate the peltier junction currents via pwm set by PID, and suddenly it doesn't look so far fetched, does it?
The button cell has an internal resistance in this circuit, basically the chemical reactions inside are wimpy so you can only pull a limited amount of current before the voltage sags. And as you know, a voltage drop is what you would observe across a resistor. Therefore, the battery is acting as the resistor despite not being an obvious one.
It’s not burning out. It’s exhibiting a reversible color shift that all leds do when supercooled. How the hell do you look at it being dipped in liquid nitrogen and come to the conclusion that”it’s overheating”.
An LEDs color is set by the band gap. If you cool an LED down with liquid nitrogen like in this video then the semiconductor contracts and the band gap increases. Higher band gap energy = shorter wavelength. Shorter wavelength = bluer light.
This is simply the temperature dependency of the band gap.
From short to long wavelengths (roughly): UV, Violet, Deep Blue, Blue, Cyan, Green, Yellow, Orange, Red, IR.
If you reverse that you see that a Yellow LED, when cooled down low enough, will become green.
Edit: Forgot to say that not all LED colors behave the same. For example White LEDs just shift the white balance weirdly. Blue LEDs (InGan) only show a small shift because blue is already short wavelength and cooling it down shifts it into the UV range quickly (which we cant see).
Cool! The liquid nitrogen is causing the semiconductors band gap to shrink which effects the color of the LED via photon energy and shortening wavelength. Warn it up and it returns to normal.
This person is sciencing hard! Thank you for your science!
They make you learn about semiconductors when you do a BSEE in the US.
Not that I'm complaining. Semiconductor and VLSI classes were certified NEATO.
I understand none of those acronyms
US stands for "United States".
What's United States stand for?
Not much, these days
queue darude sandstorm
HEYOOOO!
They're not. They're saying the exact opposite of the truth.
Quick! Warm them up!
"Any sufficiently advanced technology is indistinguishable from magic." - Arthur C. Clarke
This is an exception and a special effect that only covers orange LEDs and low temperatures.
Not yellow.
“They’re sciencing hard” - ah yes the phenomenon of cooling materials down and .. expanding? Not quite.
Remember in elementary school, for us it was 3rd grade, a science class demo on how an empty can or bottle can be heated and then dunked into cold water, causing it to rapidly crumple itself up?
Or a metal ring captive behind a metal ball on the end of a shaft but after hitting the ring with a torch for a few moments, it can be slid over the ball?
Cooling down this specific type of LED by such a significant amount from ambient opens the gap, because the material is contracting, enough to where it can emit different wavelength of light.
Theres things that can prevent this too. The driving circuit not permitting adequate current or forward voltage for example.
Room temperature examples of this circuit limitation include cheap toys with Red/Green/Blue LEDs driven by a tiny coin-cell battery.. as the battery voltage drops eventually you’ll only see red and green light.
Further voltage decline will yield only red light as diodes require a certain electrical potential (“forward” voltage) to function and different color photons need different voltages to be emitted. Red light being the flavor of visible light with the longest wavelength and thus the lowest energy
Explanation is just as cool and it makes sense
on the contrary, the bandgap widens, allowing higher energy photons to pass.
edit: common misconception, more info here
https://www.reddit.com/r/TheRandomest/s/LNIDrC0g2R
It causes the band gap to widen actually. When temperature drops, vibrations decrease and the crystal lattice contracts slightly, increasing the band gap energy.
Why does the lattice contraction increase the band gap?
The band gap is created from said lattices, but the n and p lattices change also, changing doping concentrations as they expand or contract
That's great info, i'm sure, but i don't see how it answers the question of why "mechanically," the contraction of the lattice increases the band gap energy, and doesn't - say - decrease it.
Because chemical structures use orbitals, which are energy dependent and what influence the energy gaps. If you change the orbitals (changing the structure) you change the gap (the energy needed to go from one place to another), I think.
This one time, at band gap...
Maybe I’m stupid but doesn’t a lower band gap mean lower energy and therefore longer wavelength?
I had the same thought, and apparently so did others because a bunch of other people have responded. Some of them brought receipts.
Nuh uh, obviously the liquid nitrogen is slowing the light causing it to blue shift /s
*affects
Thank you. This bothered me too lol
It bothers me that you grammar Nazis think language is composed of objective rules rather than a way for us to communicate with each other. Changing the E to an A doesn't make it any easier to understand what they were trying to communicate.
[deleted]
Those are two entirely different sentences. Did you give my wife a dollar or did you have sex with her? There's no other way to reasonably interpret that person's comment.
The band gap affects the color of the LED.
or
The band gap effects the color of the LED
LOL, you fell for it
https://www.explainxkcd.com/wiki/index.php/326:_Effect_an_Effect
Your link explains that the effect as a verb means causing and affect means changing. The color changes so affect would be correct.
No, since it causes the color change, so both work.
r/confidentlyincorrect
No, the bandgap is widening. The colour is shifting towards blue, which is higher energy, matching the wider bandgap.
Doesn't the band gap increase because of the colder temperature?
It broadens* larger gaps produce shorter wavelenghts (going from yellow to green, since higher energy is needed to bridge it). It is also known that semiconductors gain resistance with lower temperatures, which is what causes the the higher power here (and therefore different wavelenght), I think.
It's reassuring to hear that the experience of getting affected by shrinkage is universal.
Is this also why red LEDs turn yellow when over-volted?
‘I looked then and saw that his robes, which had seemed white, were not so, but were woven of all colours, and if he moved they shimmered and changed hue so that the eye was bewildered. ‘“I liked white better,” I said. ‘“White!” he sneered. “It serves as a beginning. White cloth may be dyed. The white page can be overwritten; and the white light can be broken.” —LoTR
This guy leds
can confirm, I heard a few of those words before!
Thank you science hippie 🥹
We can make some super cool t.v
smells like science in here
Thanks for your enlightenment
Wait, shouldn’t the band gap get wider? A wider gap means more energy, hence shorter wavelength.
you got the relationship inversed. band gap increases and energy of light emitted increases (wavelength decreases).
god i love black excellence…
In modern internet someone should comment that this answer is a fake news. /s
ironically this answer is fake news. The bandgap increases due to there being less thermal energy. An increased band gap means that the photons that are released will have increased energy and thus a shorter wavelength or a higher frequency.
Took them forever to make the blue LED when they could’ve just permanently sunk a green one in liquid nitrogen smh
They used Gallium compounds to make blue leds. It was a less researched Gallium Nitride compound in the mid 1990s.
We’ve got this bloke to thank.
Well aware, I knew it was far more difficult than “bigger band gap”, I was hoping the “smh” at the end was enough to convey sarcasm
The veritasium video on the whole journey is probably my favourite video of his!
I still remember the PS2's blue LED.... So mesmerizing. It was probably a lot of people's first experience with one
You literally cannot look away
Now they are everywhere
While true, I'd emphasize that they were nitride compounds. GaAs had been used for quite a bit longer to make red emitters, so the innovation related to the nitride.
Love seeing the miserable "smart" people get downvoted into oblivion
“It just looks sciencey”
I'm confused, the ones that aren't deleted are just expressing concerns?
It's the ones that were deleted in shame
“Actually 🤓 this is NOT magic.
What you are witnessing here is a very basic application of physics, neuroscience, quantum mechanics, mechanical engineering, materials science, optics, chemistry, advanced mathematics and probably a bit of thermodynamics.
I figured it out in about 0.3 seconds while casually scrolling, because unlike some people, I understand how the universe works.
The fact that this subreddit is called blackmagicfuckery is, of course, deeply misleading and intellectually offensive to me personally.
Please stop enjoying things incorrectly. Thank you.”
I’m color blind. I didn’t see much of a change. What did I miss?
The LED glow went from yellow to green in the liquid nitrogen, and back to yellow after warming back up.
Same, it just looked slight brighter to me.
I knew someone would have already asked this. Thanks!
LED aside, isn't it rather dangerous to get so close to liquid nitrogen gloveless? I know the Leidenfrost effect makes it fall off you if you get splashed, but that's just sitting there and if you dip your finger accidentally it's toast, no?
It will frostbite you pretty hard if you dip it. This is why cooking programmes where you see people using it with no PPE piss me off.
Edit: I admire everyone’s confidence, but note that during my chemistry degree and my early career as an organic chemist, we would not go near dangerous goods, such as liquid nitrogen, without PPE (and, yes, ventilation — it is of course an asphyxiant). It is a Class 2.2 Dangerous Good. If you use Dangerous Goods without risk assessment, and controls such as at the very least PPE, you generally increase the risk of injury.
There are of course contexts in which we all handle DGs day-to-day without PPE; notably filling our cars with petrol (gasoline, a Class 3 Flammable DG). This has other controls incorporated like engineering controls; e.g. designs of the nozzles at the pump, and the filler neck on your tank.
Splashing LN around on MasterChef or having open bowls of it is unwise. I’m fully aware of the Leidenfrost effect, but Leidenfrost won’t stop that stuff blinding you if you splash it in your eyes, or suffocating you (or the next person to enter the room), for example.
Don’t be a panic-merchant, sure — but know that Dangerous Goods, by definition, don’t give a rat’s about how brave, confident or flippant you are.
Not true, thanks to the Leidenfrost effect you’d have to be doing something pretty silly to harm yourself with LN2. PPE is not generally required.
I did a lot of very silly things with liquid nitrogen when I worked in a lab, never had any problems. Course the main danger is asphyxiation.
Like say, get it on your clothes.
Yeah it’s perfectly safe if it splashes on your clothes. When I was a hilarious student we used to enjoy putting people’s wooly hats into nitrogen and then moulding them into phallic shapes before putting them back onto somebody’s head.
Fair lol, my ignorance shows. I thought the temperature becomes an issue when its solid against your skin as opposed to the liquid(/gas).
At my job we just pour it one handed no ppe it ain’t that bad dog
Unless you have the reflexes of a sloth, you'd naturally yank your hand back way before any permanent damage was done. You'd probably have some 1st degree burns though.
It’s also in a bowl that you can see shake when he hits it with his hand several times. Possible scenario..Does touch the liquid nitrogen, yanks hand back, makes bowl flip, LN goes flying into his face and eyes. This idiot is a Darwin awards candidate.
So there's also a thing where those outdoor laser christmas lights emit dangerous wavelengths of IR when they get cold.
Good thing we never use them during the winter.
https://www.youtube.com/watch?v=9tOcUyakk0Q
Ok, that's cool and all, but the first colour was orange.
Orange, yellow, then green.
"It just looks sciency dudn't it?" made me chuckle.
I love this guy, his excitement is contagious
That bowl is a strange looking magnet
(Ik its not a magnet)
In semiconductors, the colder the temperature the higher the resistance, and higher the resistance, higher the energy emitted due to the increase in colisions, which translates in a shorter wavelenght.
That's what happens when Pomni holds her breath
Hang on a second - so you can modulate temperature to continuously sweep across a good part of the visible spectrum?
LEDs are narrow band emitters - not as sharply tuned as lasers, but close.
If you can change the exact emitted frequency by changing the temperature via something like a thermocouple embedded into the LED... that's pretty big. I think.
Edit: why down vote? Being able to produce spectrally pure light at an arbitrary wavelength is quite valuable.
I'm pretty sure that's not what a thermocouple does lol. Thermocouples are used to measure temperature differences, which induce a voltage in the thermocouple due to the Seebeck effect. This also works in reverse, but the device is called something else: a Peltier cooler. Anyway, I think the reason you're being downvoted is because the idea isn't as practical as you might think. Basically, temperature control is hard. Being able to tune the light to exactly the wavelength you want will be tricky, especially if the environment isn't climate controlled.
Sigh. If you run current across a thermocouple, you induce a temperature difference across the junctions - heating one, and cooling the other, depending on the direction of the current.
This is the peltier effect, and cascade peltier systems can achieve ~ -90c from room temperature
https://m.youtube.com/watch?v=ImiSpAjKjss
Add in a closed loop control system via an embedded thermistor, modulate the peltier junction currents via pwm set by PID, and suddenly it doesn't look so far fetched, does it?
I'm glad you agree that it's called a Peltier cooler
It's the same thermocouple.
You're leveraging either the Peltier or Seebeck effects depending on how you use it - heat pumping and sensing/power generation respectively.
Yellol ED
How???
Don’t quote me on this, but it might be physics.
I love that he is playing with liquid nitrogen with his bare hands.
Science, Bitch!
So, Cold really is Blue colored? Noice.
That's not "cool"... That's freezing!
I’m colorblind and not impressed by the slightest
By the slightest what?
Welcome to the kill count, where we Tally up the victims in all our latest horror series.
Band gap shrinks with decrease in temperature.
But the frequency of the light goes up... which means more energy. Doesn't that mean the band gap widened?
You're right.
We all learned as kids, heat expands and cold contracts.
/r/guysbeingdudes
You are missing the resistor, the led is gonna pop.
The button cell has an internal resistance in this circuit, basically the chemical reactions inside are wimpy so you can only pull a limited amount of current before the voltage sags. And as you know, a voltage drop is what you would observe across a resistor. Therefore, the battery is acting as the resistor despite not being an obvious one.
When I was putting my leds directly on a battery they popped after a while.
Was it a button cell specifically?
[deleted]
Good thing it's not in water?
And it’s a led bulb. Even if it were water the wires are neither getting wet, nor using enough electricity to matter.
He also gets excited inflating tires.
[deleted]
It’s not burning out. It’s exhibiting a reversible color shift that all leds do when supercooled. How the hell do you look at it being dipped in liquid nitrogen and come to the conclusion that”it’s overheating”.
They think freezer burn is a literal burn
That is completely wrong.
An LEDs color is set by the band gap. If you cool an LED down with liquid nitrogen like in this video then the semiconductor contracts and the band gap increases. Higher band gap energy = shorter wavelength. Shorter wavelength = bluer light.
This is simply the temperature dependency of the band gap.
From short to long wavelengths (roughly): UV, Violet, Deep Blue, Blue, Cyan, Green, Yellow, Orange, Red, IR.
If you reverse that you see that a Yellow LED, when cooled down low enough, will become green.
Edit: Forgot to say that not all LED colors behave the same. For example White LEDs just shift the white balance weirdly. Blue LEDs (InGan) only show a small shift because blue is already short wavelength and cooling it down shifts it into the UV range quickly (which we cant see).
Yes, it’s just science. But then given magic doesn’t actually exist, all black magic fuckery is just science.
But the science is not the LED burning out. It’s a yellow LED that is turning green due to a change in the band gap.
You realise nothing posted here will be actual magic right?
why would it be overheating
Do you think liquid nitrogen ... heats things up???