retrolefty:
The problem with that is that Vf is not a fixed value, but rather varies from led to led and changes with temperature. So string will undergo variable brightness and even might turn off or over current the voltage source. Current must be managed externally either with series resistor or driving the string with a constant current source.
Ok so must the vs-vf never equal zero then? Should you power supply always supply more voltage than the total voltage drop from the LED's? Is it correct if I say that?