Re: Can 1W LED's be replaced with 3W LED's ?
Dropping a Lux III in place of a Lux I won't make too much of a difference, unless you're going from an exceptionally poor Lux I bin to an exceptional Lux III bin.
All things being equal, if you drop a Lux III in place of a Lux I, not much will change. It'll be about the same brightness, have about the same Vf, and about the same amount of current will flow.
You would need to increase the current to the Lux III to see a huge difference. Just dropping it in place of a Lux I won't do that. So you would have to modify the circuit to take full advantage of the Lux III.
The number of batteries required depends on the LED, circuit, runtime you want, etc.
For simple resistored setups, you need more voltage than the Vf of the LED. Then you pick a resistor that will drop the appropriate voltage at the required current. You can drive LEDs off a single cell if the right circuit is used (boost), and you can use many many cells if using a buck circuit.
The rediculous "OMG X WATTS!!!" lights are quoting the power consumption from the batteries, not the amount of power being dissipated in the LED. It's easy to make any light with any power dissipation, all while producing the same amount of light as lights using much less power. The LEDs in those lights aren't significantly overdriven compared to other lights, they are simply wasting battery power (and consequently your money) in big resistors, just to have a huge number that they can market...because more watts must be better, right? It's purely a marketing gimmick, and is bordering on false advertising.
I can make a 12W luxeon light by using 4 123As in series and a resistor, and running it at 1A. The resistor would be 8.2 ohms. 3.8W would be used by the LED, and 8.2W would be burned up in the resistor and wasted as heat. That 8.2W is a total waste, and would just be making people spend twice as much on batteries as they should be for the amount of light...but hey, I've got a "12W" light, so it must be better than some "3W" light, right?