Luxeon 5W from 1.2V cell????????????

Has anyone tried driving a luxeon five watt white led
from a 1.2V cell using a MAX1674/6/6 IC
I have driven a whole bunch of "normal" 5mm leds from this
little chip but I have a luxeon on order to be recieved
tommorrow and I was wondering if any one had any ideas
or possible experience with this.
any comments on the luxeon with the standard collimator with regards to brightness/beam shape/depth would be appreciated also?

Well - 'reading' the MAX1674etc datasheet shows VOUT max of 5.5V and 300mA max drive. Since a White 5W luxeon requires around 7V (Vf) and 700mA to drive at spec - the answer would appear to be NO.

george.

5w LS needs over 6.5V/700mA to drive. Let's assume you can build a 100% efficiency converter, so you go by this:

6.5V*0.7A/1.2V=3.8A

OK, maybe you can get around 3.8A with a C or D cell---then you consider the efficiency---from the experience I gathered building Arc AAA mod and Solitaire mod the efficiency of a boost converter drops steadily as the power output increases. You will be lucky if at 1.2V/5W level you can maintain a 50% efficiency. Then it's 7.6A Average battery draw---consider you need pulse current several times in magnitude, your transistor would need to pump some 20+A from a 1.2V source---where can you find those transistors?

thanks guys, I appreciate your help.
I think higher voltage cells are the answer, and a converter/regulator with higher power output.