
I've used these in the past to indicate power direction/polarity...work great
Now I'm using 8 of these to build a network cable tester, they work good but they should sell them cheaper in a multipack.
Used this as a voltage indicator. With a 100 ohnm resistor, at 4.9 volts the led is red at 5.0 volts. Could be used with any voltage point, just calculate the proper resistor value