Years ago, I had a 2 lead LED that would be green with one polarity of DC, red with the polarity reversed and yellow with AC volts. I can't find these anymore. Are they no longer made? I have seen LED's with 4 leads that are multi colored, but not the kind I had.

 

Welcome to AAC

Years ago, I had a 2 lead LED that would be green with one polarity of DC, red with the polarity reversed and yellow with AC volts. I can't find these anymore. Are they no longer made?

Jameco has them. Should be readily available from multiple sources. eBay came up, but I wouldn't buy there if you need to know the specs. Jameco has datasheets for just about everything they sell.

You may have had problems finding them because you called them tri-color and they're bi-color.

 

Thanks!

 

My experience with bicolor LEDs is the the colors are red, green, and "not quite red".

 

Same experience with the ambiguous yellow color.

One must have different resistance values for the forward and reverse current, to equalize their unequal brightness.

 

Same experience with the ambigutous yellow color.

One must have different resistance values for the forward and reverse current, to equalize their unequal brightness.

Doesn't the red and green (primary light colors) mix to form yellow?

 

Same experience with the ambiguous yellow color.

One must have different resistance values for the forward and reverse current, to equalize their unequal brightness.

Doesn't the red and green (primary light colors) mix to produce yellow?

 

Doesn't the red and green (primary light colors) mix to form yellow?

It depends on the relative brightness of the red and green LEDs and the duty cycles for red and green.

From the datasheet for the 3mm LED I referenced:

You can see that the red green LED is more than twice as bright as the green red.
EDIT: corrected colors, old bias

 

Doesn't the red and green (primary light colors) mix to form yellow?

Red and green can be mixed to make any colour between red and green. If they are in equal quantities you get yellow. Slightly more red and you get orange.

 

If you have ever tried mixing to get yellow, you would understand. The color only looks yellow in a very narrow range of ratios.

 

From the datasheet for the 3mm LED I referenced:
View attachment 301764
You can see that the red LED is more than twice as bright as the green.

No, the The green LED produces a brightness of typically 5mcd but the red produces typically only 2mcd.

In the olden days, a red and green LED produced almost the same brightness but modern green LEDs are much brighter than the old ones.