Not too bright

I’ve been thinking about a module that would have six LEDs on the front panel (and maybe another one that would have ten), and something I noticed in a breadboard test is that if one of those LEDs was a diffused green one from Tayda (SKU A-1553), I was definitely seeing a change in the 12 V power rail when the LED turned off and on. Not a huge change, about 10 mV, but multiply that by six or ten and it’s really getting significant. That was with a series resistance of 470Ω (and a 5 V supply). The red LEDs (Tayda A-1554) needed a resistance of about 3.3kΩ for similar brightness, therefore a lower current, and they affected the power rail correspondingly less.

I thought I’d try some “superbright” or “ultrabright” LEDs — Tayda A-057 and A-706. Not because I wanted them brighter but because I could get similar brightness with higher series resistance, lower current. I didn’t like the result. Those LEDs are “water clear”, so they’re not diffused and the light is much brighter on-axis. So to get decent brightness off-axis, you have to run them with a low enough resistance that the on-axis brightness is blinding.

Unfortunately Tayda doesn’t carry any high brightness diffused LEDs. People have mentioned sanding the lenses to diffuse them, or coating them with something. But sanding the round lenses uniformly and keeping them round sounded to me like a real pain. You can try sanding them flat but I wanted rounded ones.

So I bought some LEDs on AliExpress here. They’re called “fog LEDs” which is apparently their term for diffused, and the brightness numbers they quote are a good bit higher than Tayda’s diffused LEDs though lower than the “superbrights”. Then again, can you rely on those numbers? I have no faith in them, especially since some of the other numbers they claim (most notably the wavelengths) don’t seem to make any sense.

They arrived today and I put one of the green ones up against a Tayda A-1553:

Top and side views of Tayda A-1553 and AE “fog green” LEDs

The AE LED is on the left and the Tayda on the right. Of course the photos don’t accurately reproduce how they look in reality but you can get an idea. The AE is diffused and is brighter than the Tayda but not blindingly so on-axis — but only because while the series resistance I used on the Tayda was 2k, on the AE it was 60k. (Power supply was 12 V.)

Forward voltages were 2k for the Tayda and 2.2k for the AE. So current, with the above resistances, was 5 mA for Tayda and 0.2 mA for AE. Presumably the latter would be far below what would make a detectable change in the power rail voltage.

To bring the brightness down to roughly comparable to the Tayda with 2k, I had to increase the AE series resistance to about 160k.

The AE is also greener than the Tayda. I never thought the Tayda looked un-green before, but next to the AE, it definitely looks a lot more yellow.

One drawback is the leads are shorter on the AE. The Tayda’s leads are just long enough that you can solder one next to a 1/4″ closed jack and it’ll reach through a hole in the front panel. The AE LEDs would need to have their leads extended to do that.

Haven’t looked at the reds yet, I assume they’ll be comparably bright with comparably low current draw. I’ll update here if I find otherwise.

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