Does Vf BIN Matter If Using A Driver?

If you use a driver to power an LS, it is set to a specific current to run at. If that is the case, does it matter what Vf LS you use since it will be driven at a constant current?

The LS will run hotter with a high Vf since the
power (v * i) is higher.

With a down converter you will likely drop out of
regulation sooner with a higher Vf since Vin minimum
is usually Vf plus a small amount.

With a boost converter the converter will draw more
current from your battery to deliver the higher power
to a high Vf, so you battery life will be reduced.

Greg

So basically when using a driver, a lower Vf BIN is ALWAYS better?

A lower vf is not always better. For an example if you plan on using a Li-ion with a peak volt of 4.2v, but rated at 3.7v.

You would not want to use a H bin (3.03-3.27v) with a Volt in of 4.2v. if voltage in exceeds vf, then effectively you go into direct drive. In this example where volt in is 3.7 to 4.2v, a better match would be K bin (3.51-3.75) safely factoring for half volt over vf. As voltage will quickly drop to 3.8 range.

In Mr Bulk's SNII direct drive built instruction, he specifies use of a high vf bin to match the 3X 123 used.

The lower the Vf, the more efficient the emitter is (typically). Most converters will be more efficient with lower Vf emitters, but there are exceptions.

When using drivers a lower Vf luxeon will have these effects:

Constant Current Driver: You'll get increased runtime with low Vf and it will run cooler.

Voltage Regulated/boost Driver: The luxeon will see more current and be driven harder than a high Vf luxeon.