Originally Posted by hairytoes
OK, Jeff, you are unconvinced.
How about this?
The Buckpuck current source will take input voltages from 6V - 30V. It will output 1A current, as required for the K2, regardless of the input voltage.
That means you can use a wide range of battery packs, and the light output doesn't drop as the battery gets low.
I disagree about the easier to build aspect. The buckpuck is a sealed, waterproof block, with 4 wires. I just put them in tamaya connectors and plugged it together.
Yes, it's very true that the buckpuck can be powered from a wide range of voltage sources. I also agree that it's probably the ideal way to run a Luxeon emitter (in fact I use one myself). However, it's not really necessary for running a string of regular LEDs.
Also, you can get a buckpuck for much less (in North America) from
www.luxeonstar.com.
So here's my final answer:
For running one or more Luxeon emitters, use a current source, like the buckpuck.
For running strings of 5mm LEDs, just use resistors matched for voltage.