Let’s Look At Some Cool Old LEDs

LEDs are now a mature technology, with all manner of colors and flavors available. However, back in the 1970s, it was early days for this fledgling display tech, and things looked very different. [IMSAI Guy] happened to work at the optoelectronics division of Hewlett-Packard during their development of LED displays, and has a handful of prototypes from those heady days.

The video is a great look at not only vintage display hardware, but also rarely seen prototypes that seldom left the HP offices. Matrix, 7-segment and even 16-segment devices are all in attendance here. There’s great macro photography of the packages, including the now-forgotten bubble displays as well as hermetically sealed glass packages. The parts all have a uniquely 1970s look, drenched in gold plating and otherwise just looking very expensive.

The followup video breaks out the microscope and powers up the displays. [IMSAI Guy] shares some useful tips on how to best tinker with unknown LED parts, as well as knowledge about the chemical compounds and manufacturing processes involved in LED production. If you don’t know your III-V compounds from your II-VI compounds, prepare to learn.

It’s always interesting to take a look back, and even better to get a peek at the experiments of engineers of the past.

If you’re wondering about applications of this hardware, we’ve seen messageboards and watches before. Video after the break.

17 thoughts on “Let’s Look At Some Cool Old LEDs

  1. Serious question but the early LEDs from 80s has slightly different color (almost slightly warmer?) from modern HiE LEDs. Amber/yellow for example seemed more like regular dandelion yellow from 80s while modern yellow LED looks more like pure yellow. Also modern LED can still be “too bright” even if I used 100k resistor on 5v system while older LED looks fine with just 330 ohms resistor on 5v

    Would this be due to changing elements used on LED dies? And is there a way to get modern LED with older style color?

      1. That’s an interesting thought. Since the bandgap of the semiconductor determines the wavelength of light emitted, does aging of the semiconductor have any effect say due to something like contamination/breakdown or something else?

      2. No, the 80s LEDs really used different dopants, they were less efficient and typical colours were slightly different. Today not all LEDs are the same either, for example if you look hard enough you can find much more orangey yellow than typical almost slightly greenish yellow.

    1. I’ve noticed that too. I have some old red leds and they are a deeper red than ‘modern’ ones. I haven’t bothered to research, but I wonder if the older leds emit in certain wavelengths because that is all they could do with materials at the time and if modern leds of the same wavelengths are available.

          1. I saw clear cased LEDs in the shop when I wanted to buy blue ones.
            “I want a blue LED”
            “There are no blue ones”
            “But you have them in the drawer here!”
            “No, these are infrared”
            “OK, then give me some of the white ones beside, I put a blue cover over it.”
            “The are red, just clear case”

            In the mid 80ies, when even SiC blue was far away.

      1. But since LEDs emit only a tiny sliver of visible spectrum, changing the color of the case doesn’t change the color of the light being emitted. A diode that emits 633nm light will always produce 633nm light, no matter how you filter it: All the filter can do is make it dimmer.

    2. You can find LEDs in all kinds of native colors, including the way they used to be.

      For the deep red, look for a longer wavelength. The newer red seem d to show up with the advent of LED tail lights, which were the early prime driver of high-output LEDs.

      My own favorite is the intense green that nobody seems to use in products anymore as things shifted to a much more yellow color.

      But they’re all still out there, sure as you can still find a 555. There’s efficiency and packaging tradeoffs, but you can do it.

      1. I saw clear cased LEDs in the shop when I wanted to buy blue ones.
        “I want a blue LED”
        “There are no blue ones”
        “But you have them in the drawer here!”
        “No, these are infrared”
        “OK, then give me some of the white ones beside, I put a blue cover over it.”
        “The are red, just clear case”

        In the mid 80ies, when even SiC blue was far away.

      2. The below comment about clear cased LEDs got misplaced.

        I have a device (battery operated stapler), which has a blindingly intense deep green power LED on top. Looks like a normal 5mm LED. They should have put it on the bottom, it would function as workplace illumination. :-)

  2. Neat. I recall the hex LED’s with the decoders on board. We used them in a product in the mid 80’s. I have a stash of them “someplace”. I wanted to make a hex clock but never got around to it.

    It is funny you are from HP as I was literally just chatting with a pal about old HP LEDs. Back in the day you guys introduced the high brightness LED’s. I noticed on the data sheets that they too the same drive as the normal LED’s. A quick look at the datasheet once they arrived proved me correct. The only real difference was in the reflector behind the die or the lens in front of it. The high brightness LED’s or yore had a much narrower viewing angle.

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