I remember someone saying that "pure green" LEDs (GaN, InGaN) were quite visible at very low current levels. Does anyone know an appropriate current for such an LED to make it fairly visible from a few feet away in a moderately lit room? 10uA, 100uA?
Oh, I'd think you'd need more than 100 uA. Many of them can be viewed with the current from the "diode test" function of a DVM. I don't know what that current is, but I'd guess it might be around 100 - 500 uA. This generally gets them bright enough that you can detect which polarity is the right one, but more likely to be seen from inches, not feet. So, for visibility from feet, you would maybe need a mA, I might guess.
Some recent white and blue LEDs are totally amazing, and quite bright with the DVM.
Jon
A good green LED is visible in office light at 1 uA, but 100-200 uA is more reasonable for an LED that's directly visible on a PC board. A few mA is OK to backlight a window in a polycarb sticker.
Try it!
Dark adapted at 2AM, up close, I saw a green LED make visible light at about 800 pA.
The ones I used a few years ago were quite visible in broad daylight at 1mA.
The InGaN LEDs appear significantly brighter.
Some LEDs are more perfect than others. You can buy a bag and pick the best.
Or read the data sheets!
I've only seen data sheets claiming that LEDs are not tested below XX percent of their normal operating current. Which ones list microamp sensitivity and leakage?
They are pretty linear in the ranges we're considering here. Go for the most efficient.
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