First, can someone confirm that the "LED part" of the circuit "has a purpose" (I don't know how to say this), like explained in part 3 of this comment.
Then, is it possible to change the LED with one of a different color, without messing up the behavior of the circuit ? I would like to put a purple one instead of the red one which is connected right now.
My intent was to remove the LED and measure the voltage "at its place", and use the value as the supply voltage to calculate a resistor value. That would lead me to add a resistor+LED in place of the current LED (or maybe just the new LED if the calculous gives me a resistor value of zero ?).
Or is it a bad idea and there is no other solution than to let the current LED in place ?
Thanks a lot to whoever can help me !