I just finished building this light last week. It took me a few weeks to figure out, along with some burned up components. It is very bright and I plan on using it for a video light for shooting caving trips. The run time is around 28 minutes and the color temp is around 4300k. There are LEDs that are 500W, but they runs on 70V, 8amps and would require very expensive batteries to run it (4 @ $180/ea). Not really cost effective.
Anyways have a look. The video is about 4 minutes.
There is also a link in the video that takes you to candlepowerforums where I have the build instructions posted.https://www.youtube.com/watch?v=TsYvcV_qqPo
Dayton Underground Grotto