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It was almost impossible to make the blue LED [video]

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Re: It was almost impossible to make the blue LED [video]

#141

Post by willis936 »

hugryhoop wrote: post #26
vardump wrote: post #2

Assuming everything is reported fairly, I really can't imagine being Nichia's customer. Ever. Sacking and not compensating the employee that single-handedly made Nichia successful by inventing a working blue LED and saving Nichia from bankruptcy is just not acceptable.

It's complicated. For 1 employee which disobeyed orders and saved the company you'll have 99 which disobeyed orders and don't produce anything useful or even made harm. This is called the Halo effect.

I'm not sure it is the Halo effect here. Imagine how much more money they would have made if more employees ignored the new CEO, or if there was a different CEO.

Re: It was almost impossible to make the blue LED [video]

#142

Post by amarant »

01HNNWZ0MV43FF wrote: post #133
cypherpunks01 wrote: post #48

I thought this was a really well-produced video! It's difficult to communicate science to the public in an accessible way at the right level, and I think Derek does a commendable job. I really liked the LED explanation at the 4:00 mark. Can anyone who is familiar with semiconductor physics opine on how well this explanation models the reality?

I liked it, though it bugs me a little when people equate infrared and heat. Infrared is light. Light can heat things, and hot things can glow, but "infrared is heat" isn't exactly right.

I know basically nothing about physics, so sorry if this is a dumb question.

The existence of infrared LEDs seems to indicate to me that infrared light can exist without heat.

The existence of infrared thermometers seems to imply that hot stuff radiates infrared light, at least usually.

So my question is, is there any case where heat does not cause infrared radiation? What are those cases? Some special materials? Special colours(perhaps outside the visible spectrum)?

Re: It was almost impossible to make the blue LED [video]

#143

Post by JohnFen »

cypherpunks01 wrote: post #48

I thought this was a really well-produced video! It's difficult to communicate science to the public in an accessible way at the right level, and I think Derek does a commendable job. I really liked the LED explanation at the 4:00 mark. Can anyone who is familiar with semiconductor physics opine on how well this explanation models the reality?

I agree. Setting how LEDs work aside, I never really got how semiconductors worked, despite reading about it and talking with experts for years, until this video.

I mean, I could explain how they worked in the same ways that they were explained to me, but I couldn't connect those explanations to a true physical understanding.

But thanks to this, I finally actually understand.

Also, the LED story was fascinating.

Re: It was almost impossible to make the blue LED [video]

#145

Post by willis936 »

The first ten minutes is the best explanation of conductors, insulators, and semiconductors I’ve seen. The rest is a gripping human story with science sprinkled in. The maker / experimentalist spirit strongly resonates with me. There’s a line at the end for climate change and fusion folks.

This video is to adult me what Back to the Future was to kid me: it has it all.

Re: It was almost impossible to make the blue LED [video]

#146

Post by JohnFen »

mb_72 wrote: post #116

I remember when blue LEDs started appearing in guitar FX pedals just out of novelty,resulting in a pedals becoming harder to use as when the pedal was on the brightness meant visibility of the controls was reduced. On pedals I made I always used fine sandpaper to increase the diffusion of each LED, and the result was significantly better. Early blue LEDs,especially, seemed to have a very narrow projection angle.

Blue LEDs are an amazing and badly needed advance -- but you're right, the abuse of blue LEDs has been, and continues to be, really awful.

Re: It was almost impossible to make the blue LED [video]

#147

Post by crtified »

After the blue LED came onto the market in the 1990s, it took less than a decade for them to become shelf items of a couple dollars each at electronics retailers.

It was also around that time that web-based communities of computer technicians really took off. Web forums, etc.

The coincidence led (yup!) to a love-at-first-sight relationship. Funny as it may seem now, being a mere 20 years later (or: "holy crap, it's been 20 years!, how did that happen??"), there were a few years there in the 2000-2005 region during which the de-riguer of computer nerdery was to go blue LED crazy.

It felt elite, cutting edge, rare, oh-so-techy. And it's funny now, to look back at the windowed PC cases full of LEDs and garishly lit by cold cathode tubes, with our mouses and speakers and other electronic gadgets painstakingly swapped over to blue.

And within a further couple of years - from about 2005 onward, if not sooner - the commercial market had taken over the trend and made it boring, passe. We hackers and overclockers weren't interested any more. Indeed, these ultra bright things began to get annoying. Within about 5 years the modding scene's blue LED craze began, peaked, commercialised, became a liability ... at which point we began to hastily obscure our blinding modifications with another, very different, product whose very identity hinges upon the colour blue : Blu-Tack! [0]

So where did it all end up, this short-lived cultural crossover between blue LEDs and hackers? Well, basically, the commercial market morphed into the "RGB" movement of lit-up computer hardware. RGB fans, RGB cases, RGB panels on graphics cards, etc. But I still think the blue LED is pretty cool.

[0] https://en.wikipedia.org/wiki/Blu_Tack

Re: It was almost impossible to make the blue LED [video]

#148

Post by thirdhaf »

cypherpunks01 wrote: post #48

I thought this was a really well-produced video! It's difficult to communicate science to the public in an accessible way at the right level, and I think Derek does a commendable job. I really liked the LED explanation at the 4:00 mark. Can anyone who is familiar with semiconductor physics opine on how well this explanation models the reality?

The explanation is really well done, it captures the essence of the Pauli exclusion principle without delving too deeply into the weeds. In my opinion the best part of the video is the explanation of the "hole" quasiparticle at 6:10 (I learned this as a pseudo-particle but will defer to Wikipedia [1]).

While a great introduction to semiconductor behavior this does gloss over a very important detail namely direct vs indirect semicondoctors as some others have mentioned. In the video the detail that's glossed over relates to the nature of crystals, namely that they're highly ordered repeating structures but that they don't look the same when viewed from every direction. This means that there isn't a single band-gap but multiple ones depending on the direction of the crystal you're contemplating.

At this point you may reasonably ask why the direction matters and now we unfortunately get deep into the weeds with quantum mechanics again. When a single photon is absorbed in the semiconductor system both momentum and energy must be conserved. The momentum of the photon for something like the Silicon bandgap is quite small (something like the equivalent of an electron traveling at 1500m/s) while the momentum of room-temperature conduction electrons is substantially faster [2] so as a very slight simplification transitions due to the absorption of photons are not accompanied by a change in momentum and so we only care about the band structure (and the accompanying free carriers) associated with a particular crystal direction.

In particular in Silicon you have what's called an indirect bandgap, namely the minimum energy conduction band electrons have a different momentum from the valence band holes ([3]) and as a consequence while you can _absorb_ a photon in order to make a detector you cannot make it efficiently _emit_ a photon as an LED should (something the video got wrong).

None of this matters for the heart of the video, which focuses blue LEDs in the GaN materials system which is definitely a direct bandgap material, however if someone does manage to create a manufacturable light emitter in pure Silicon expect an absolute revolution with regards to optical computing and photonics. (Not for lack of trying, this has been the holy grail for at least 20 years, possibly longer)

[1] https://en.wikipedia.org/wiki/Quasiparticle [2] https://www.chu.berkeley.edu/wp-content/uploads/2020/01/Chen... [3] https://www.iue.tuwien.ac.at/phd/wessner/node31.html

Re: It was almost impossible to make the blue LED [video]

#149

Post by elevatedastalt »

amarant wrote: post #142
01HNNWZ0MV43FF wrote: post #133

Earlier quoted context omitted.

I liked it, though it bugs me a little when people equate infrared and heat. Infrared is light. Light can heat things, and hot things can glow, but "infrared is heat" isn't exactly right.

I know basically nothing about physics, so sorry if this is a dumb question. The existence of infrared LEDs seems to indicate to me that infrared light can exist without heat. The existence of infrared thermometers seems to imply that hot stuff radiates infrared light, at least usually. So my question is, is there any case where heat does not cause infrared radiation? What are those cases? Some special materials? Spe…

That's a good question. All bodies above the temperature of absolute zero emit electromagnetic radiation across the whole spectrum (this is called Black-body radiation). Think of it as a mixture of different amounts of light of every possible wavelength.

However, what the exact mixture is depends on the temperature of the body. As the body gets hotter, the 'peak' wavelength, i.e. the wavelength whose "amount" is highest in the mixture decreases.

Objects at room temperature emit most of their energy outside of the visible spectrum, so they are not 'visible' in the dark. However, as you heat them up, the radiation mixture moves towards lower wavelengths, closer to infra-red. Heat it up further and things become red hot, yellow, blue hot and so on.

Infra-red LEDs produce light of the the specific infrared wavelength through semi-conductors. They have nothing to do with the black-body radiation one associates with 'hot' objects.

Re: It was almost impossible to make the blue LED [video]

#150

Post by maxglute »

Am4TIfIsER0ppos wrote: post #5

If only it was impossible. Blue leds are abominable! [EDIT] I hate white ones too so the replies aren't exactly selling them!

Blue leds also gave birth to purple leds, which for some reason every condo building has multiple units lit up like vampire dens.
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