when overdriving 5mm leds that are in parallel, the vf's can be become
mismatched and the led with the highest vf may not light up.
the low vf leds are sucking up extra current..causing a large voltage drop that
ends up starving that one led.
I don't understand that.
If several LEDs are wired in parallel, the same voltage is applied to all. If they all light up at low current, how does driving the combo at higher bias reduce the voltage applied to any individual LED? Whatever the voltage applied to the combo, wouldn't it be higher when overdriven than when not?
If that is the case, I would think it unusual to see one LED lose drive as the voltage across all increases in unison.
I can imagine one mismatched (high Vf) LED in a parallel string being always underdriven, but it's a bigger leap to imagine them all working OK at low bias and then one turning off at a higher applied forward voltage.