This project draws it's insperation and technical details from dan's http://www.instructables.com/id/Ultimate-Night-Vision-Headlamp---500%2B-lumens-with-/
and his http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/
hanks to dan for his great instructables!
Where this instructable differs is that my four Cree xr-e LEDs are powered by a USB power supply. Any standard USB power supply will work with appropriate cables. My two main power supplies are a custom D cell holder and a Ryobi rechargeable power cell. I also have a plug in wall wart that will power the flashlight and a 12v outlet to USB adaptor that can be used to power it!
While using the D cell housing, the xr-e LEDs will put out a total of 840 lumens at 6v one amp! Standard USB delivers less power at 5v and half an amp but the LEDs still output a very respectable amount of light, maybe around 700 lumens. Unlike most flashlights this one does not produce a beam of light. It illuminates a 180 area in front of it! It's like having a 50 watt incandescent light at your side.
Building the flashlight cost approximately $40 us. Comparable flashlights on the market are probably smaller but cost in the range of $140. It would have cost me slightly more if I didn't have the electronics sitting around my basement from disassembled TVs and stereos.
This took me a while of mucking around with parts so I don't have pictures of the build. I can only explain what I did. Maybe if I build another I'll be able to take more pictures.
Update: We just got back from a camping trip and we brought the Mega Flashlight! We had a few days where we were trying to get the camp cleaned up for bed so animals wouldn't come around. Walking around with a directional flashlight makes it hard to see everything. I stood on the picnic table and was able to illuminate the entire campsite at once! Even though I wasn't helping clean directly, everything went much faster. Now even more I want to figure out how to hang the flashlight say from a tree or some other object.Please remember to vote for this instructable for the contest!