Canoe Bow Light Help

I need some help with a light I plan on making. I'm about to get back into canoeing again and I'm designing a custom bow light for use during night paddling. I will be modifying a mag head or machining a custom head that will house four luxIII leds. I plan to run one continuous from a 6 volt power supply. The other three I plan to run from a six volt power supply that will be switched on only when more light is needed. I need to be able to use either 4D cell alkalines or 4 Dcell rechargeables.

Here are my questions:
What circuit should I use to power a luxIII from 6 volts?

Do I run the other three direct drive or should I use some sort of circuit for them also? If so what do you suggest?

Depending on suggestions you have, what type of runtime can I expect from each setup?

Thanks for your help and expertise.

If you're fixed on 6 Volts (most probably the worst choice, since it's way too much for a single and too little for two in series), I'd suggest to put them all in parallel and run them from an adjustable DC-DC switcher.
Or use 4 NiCads and run them through an adjustable, well cooled linear regulator.
Selecting between 1 and 4 LEDs for brightness reasons only makes sense for a direct drive (or resistored) setup - not a good choice for your boundary conditions. If you also want to vary beam shape, it might be different (and still more complicated...)
You may want to check the Elektrolumens forum, though, with respect to bike lights and hex lights.

Bye
Markus

I'm not set on 6 volts, I just already have holders with a 4d cell configuration.

What voltage/regulator setup do you suggest for a single luxIII and for 3 luxIII wired together?

Long runtime is a plus.

Why not wire 3 LED's in series using a Fatman converter and external dimming resistor pot? Why use 4? Three also allows for use in a Mag head with a tri lens.

See this thread: Fatman lives

--
Jeff