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positivecynik t1_j7ln9pe wrote

This is really specifically wild for me to stumble onto here. Let me explain. In the early 90s, a few of us in the clubs were into the whole "cyberpunk" movement that was pretty new back then.

Some club denizens went as far as to create electronic apparel, with an LED or two, and one guy even made a skin temp sensor and connected it to an LED bar graph, so the more he exerted himself the higher his temp would show on his arm.

Anyway.... everyone has either red or green or yellow. I wanted a blue. Couldn't find one.

Internet was pretty limited back then, so a lot of shopping in parts stores, catalogs. Etc....

We finally found a supplier in China that manufactured blue LEDs, but we'd have to buy like 250,000. Somehow this dude gets a hold of exactly 5 of them. He worked a deal with a store who ordered the he quantity and let him buy 5.

Craziest thing, the turn on voltage for the ones We used was 6V. So, strapping 4 AAA batteries somewhere on you would give you 6V.

These blue LEDs from China needed 5V.

Took a while, but we figured out that rechargeable batteries output 1.25V, so we used 4 of those to achieve the 5V turn on voltage. The whole thing took about a year while we figured it out.

Haven't thought about it in 30 years. Then I run across this random article telling me exactly why what I tried to do 30 years ago was so difficult.

/endstorybro

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Thelgow t1_j7luawl wrote

Funny you should mention rechargeable batteries. A while back, 14 years or so ago, I was dabbling with electronics and wanted to swap my xbox360 controller and front panel led's from Green to something else, like purple. I ordered a bunch of purples, blues, reds, etc. I wire up the purples to the controller. Nothing. And these were so small, if the soldering iron stayed on it for more than 2 seconds it literally would disappear in a puff of smoke.

Apparently I'm telling this out of order but it helps. I did the red ring on the 360 front panel with the purples fine, so I know theyre good. I replace the purples with blues and it lights right up. I put purple back, no dice. I'm fiddling around and I forget how but I plug the charging wire into the controller direct and I get flashbanged by purple lights. Similar to your story I found out the rechargables had less voltage. So the red ring front panel is hardwired and getting full juice, but wireless, no dice. Pop in the usb charger and yeah it would light up. Also confirmed regular AA's would work, but I already had all these battery packs so I wanted to stay with the lower voltage.

So I opted for a blue/red/blue/red X pattern and left the purples for the front panel. Cool side effect was that as the batteries died the blue led's would get dimmer and dimmer until you just had 2 bright red led's and then the controller would just die. I think this may be a reason they favor red for emergency systems as it seems to require less power.

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strangr_legnd_martyr t1_j7lzy1d wrote

Red LEDs do require less power. The forward voltage on a red LED is about 1.8V at 20mA. The forward voltage on a blue LED is about 3.6V. That's 36mW of power for red vs 72mW of power for blue.

Blue light has more energy than red light (higher frequency/shorter wavelength).

I think they generally favor red over blue for emergency systems, though, because red light has less effect on low-light vision. So if the power goes out, your red-lit emergency signs don't blind you in the dark.

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Thelgow t1_j7m0bd7 wrote

That too because lord knows what happens when the tape falls off my optical to rca adapter. Why this thing has a Batman spotlight built into it, I'll never know.

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Ok-disaster2022 t1_j7mdka0 wrote

However there's an issue with emergency signage. Red is the color of danger, stop, while green is safe, go. Exit signs in areas of low literacy are green and green are becoming more common in the US to be more inclusive of people who can't read.

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Marzgog t1_j7qj8dt wrote

My country has among the highest rates of literacy in the world and our exit signs are green. I don’t think inclusivity has anything to do with exit signs going green, it’s just one of those universal standards in the making.

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KentDarkmere t1_j7lqpf5 wrote

I think I would of just used a resistor in parallel with the led

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nocrashing t1_j7lxfkk wrote

Series but yeah

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Admetus t1_j7opryj wrote

Also wouldn't the internal resistance of the batteries mean those blue LEDs were drawing less than 5V? 🤔

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ItDoesntMatter59 t1_j7mws9q wrote

You are supposed to use a current limiting resistor. LEDS dont last long with excess current which you will get without one

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shalafi71 t1_j7ntsek wrote

I was arguing with a (much smarter) friend about resistors one day. He insisted that if you got the voltage right, you didn't need one. "Dude, LEDs pull amps until they burn, sometimes instantly. You have to either get stupid lucky with current and voltage or you have to use a resistor."

To this day he doesn't believe me. "Dude, take a $1 store light apart, there's a resistor soldered onto the hot lead. Every. Time. Why would China put unneeded parts in there?!"

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