I was playing with some antiquated methods of ac-dc conversion and found that this particular circuit would (at top of cycle) supply the exact difference of potention across an led to run it at standard full brightness (~20ma) in spite of the voltage the led is rated at. This means you should be able to pop any single or series stack of leds in place, put your meter leads across it and see its rated voltage if you dont know it. Just change the led value in the sim to see. Im certain there are many circuits for this but what the hell, here's one more.
