How LEDs are made (2014) • Hacker News Board

Re: How LEDs are made (2014)

#21

Post by joe_mamba » Sat, May 09, 2026, 9:08 PM UTC

WalterBright wrote: post #16

Back at Caltech, one of the students realized that the only thing limiting the brightness of an LED was heat dissipation. So, he dipped an LED into liquid nitrogen, and cranked up the current. It got pretty bright before it melted. Naturally, he realized that the clear plastic blob it was inside was an insulator. How to fix - he filed it down to the bare minimum that would hold it together. This time, it would light…

> Back at Caltech, one of the students realized that the only thing limiting the brightness of an LED was heat dissipation

It takes studying at Caltech to realize semiconductors output are limited by their heat generation? I thought everyone knew this.

Re: How LEDs are made (2014)

#22

Post by Kirby64 » Sat, May 09, 2026, 9:21 PM UTC

joe_mamba wrote: post #21

WalterBright wrote: post #16

Back at Caltech, one of the students realized that the only thing limiting the brightness of an LED was heat dissipation. So, he dipped an LED into liquid nitrogen, and cranked up the current. It got pretty bright before it melted. Naturally, he realized that the clear plastic blob it was inside was an insulator. How to fix - he filed it down to the bare minimum that would hold it together. This time, it would light…

> Back at Caltech, one of the students realized that the only thing limiting the brightness of an LED was heat dissipation It takes studying at Caltech to realize semiconductors output are limited by their heat generation? I thought everyone knew this.

The average person knows literally nothing about semiconductors. I would say it’s not very intuitive how diodes work, unless you’re an electrical engineer.

Re: How LEDs are made (2014)

#23

Post by nhecker » Sat, May 09, 2026, 9:58 PM UTC

Neat article.

I'd love to know more about how candle-flicker LEDs are assembled, because that source of [apparent] randomness is very interesting to me. I'm not sure if it's an LFSR or true HRNG, and I'm sure there are lots of different designs out there for the simulcrum of natural candle light.

You can get a better sense of their operation if you wire up the LED to an audio circuit where they'll make a pleasingly happy beep boop sound.

(Edit: There was an article somewhere that explored the entropy and concluded that their component operated on a LFSR, as they binned all the brightness outputs into integer values and waves hands did fancy math to conclude that the brightness it was likely modulated by a LFSR. I'll see if I can find it.)

(Edit 2: https://cpldcpu.com/2013/12/08/hacking-a-candleflicker-led/ here's that article for those interested. https://news.ycombinator.com/item?id=25530895 was the original submission to HN.)

De-doming these things (as discussed in another comment) is quite a chore; I de-domed 30 LEDs (candle-flicker, of course) in order to diffuse the light and fit under the keys of a small 3x10 keyboard I was building. But the effect is neat when the backlight is on as it almost looks like a shadow is randomly typing away as the entire array flickers.

Re: How LEDs are made (2014)

#24

Post by WalterBright » Sun, May 10, 2026, 12:45 AM UTC

Kirby64 wrote: post #22

joe_mamba wrote: post #21

Earlier quoted context omitted.

> Back at Caltech, one of the students realized that the only thing limiting the brightness of an LED was heat dissipation It takes studying at Caltech to realize semiconductors output are limited by their heat generation? I thought everyone knew this.

The average person knows literally nothing about semiconductors. I would say it’s not very intuitive how diodes work, unless you’re an electrical engineer.

Having taken a course in the quantum mechanics of semiconductors, I can vouch for anything involving QM is not intuitive at all.

"I think I can safely say that nobody understands quantum mechanics" -- Richard Feynman