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The Vf isn't actually a constant, it's just a very steep curve.....
http://en.wikipedia.org/wiki/Diode#Current.E2.80.93voltage_characteristic:thinking:
Please explain what you mean by this.
Vf is the forward voltage of an led and is a set value for the current that the led is driven at.
For example, one led may have a Vf of 3.2 when driven at 700ma, another might have a higher Vf of 3.6 when driven at this current. These results are reproducible for each led whenever they are driven at that current.
Its true that it can slightly change with time and use, but this is not what you implied.
When you are working out the power that the led consumes you need to multiply its Vf (at the current being supplied) by the current.
Its in this context that I said that the Vf is a constant for a particular led at a particular current.
http://en.wikipedia.org/wiki/Diode#Current.E2.80.93voltage_characteristic
While it's possible I'm reading this graph wrong, I believe what it's saying is the diode's resistance increases slightly as the voltage increases, so at 3.5v its Vf might be 3.1v but at 4.5v its Vf might be 3.5v instead.
I will leave that to the experts. I've always thought that current is a much more significant factor in affecting both led output and the forward voltage of any given led, than the voltage that is supplied.
Peak claims that 1A of current is supplied, regardless of battery voltage and this is why I'm surprised that an RCR123 seems to provide three times as much output as an ordinary CR123.
I'm pretty sure that with a CR123, the led is seeing nothing like 1A. That's the simple and most likely explanation.
In any case, this observation doesn't detract in my opinion from the LOGAN being a very nice light.
In fact, if all LOGANs follow this behaviour, which I would imagine they do, then it gives more options to the user.
Maybe it depends on the fortitude of your CR123. Perhaps the boost circuit is set up to boost to 1A from 3V, but to less from less than 3V (where the output current may sag as the input voltage sags, maybe in order to be kind to your battery). Just a guess. (shrug) Connect it to a solid 3V power supply and see what it does....
It was a brand new fresh CR123 cell that measured 3V on the multimeter.
Yeah, but, that's 3V when not loaded. It'll sag under heavy load. Clarify: I mean, as though there's an internal resistance.
When I test a brand-new CR123 on my multimeter, it outputs ~8 amps @ 3.2 volts. Granted, it only has to drop a couple tenths of a volt before can can barely manage 1 amp, but still, if the circuitry operates the way Peak says it does, a fresh-out-of-the-box CR123 should have no problem providing enough power to run the Logan at full brightness for at least a short time.
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If anyone here has a Muyshondt Nautilus R2, I'd say my Logan #6 is about as bright as the Nautilus on high mode. I think #6 is just about the perfect brightness for any of the new Peak lights, which is why all of my new Peak lights are #6's.
...... To me, that means either EasilyLed's regulator is malfunctioning, or a CR123 just can't feed the higher power rating he ordered......