One point I should have mentioned for those who might want to try this out: the variable resistor (trimpot, trim potentiometer) has three pins. Use the center pin and one of the outside pins, either one.
This system is meant for a non-technician like me to be able to build. Generally, in an LED circuit, a current controller is preferred over a voltage regulator. I don't know of a current controller than can be easily built. The LM317 can be used as a current controller, but it needs a 2W resistor to do that. I could not find resistors of the right ohm value in 2W. Voltage control is easy and uses cheap components. A constant current controller or pulsed system would be better but then the cost goes up.
There are 3W star LEDs on the same page as in the link above. I recommend trying them out. They should work with the same circuit. I have not tried the 3W LEDs yet.
Running 4 of these LEDs would require a voltage of just under 13.2V. They might work on a 12V battery, depending on your battery state of charge. The LEDs would dim as your battery voltage dropped. However when you turn a battery charger on, there would be voltage over the rating for these LEDs.
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