Not exactly a flashlight, but thought some might find it interesting. This is a project I've been keeping under wraps for quite some time now. More than a year actually. Started by building this:
16 Chip-on-Board assemblies in two strings of 8. One string is tungsten balanced (2900 K) the other is daylight balanced (5500 K). I managed to get hold of the special high CRI models, so CRI is about 95. Forward voltage is 92.5 volts on each string. Max current is 1 amp. I built the drivers with National LM5022 controller. Mostly I run it off a 24 volt supply, and it gets about 94% efficiency. It will work down to about 17 volts, and up to 32 volts input.
The heatsinking consists of bolting the LEDs to an aluminum box, 1/4" plate, with a whole bunch of surplus Pentium II heatsinks. Had it all hard anodized too. Surprisingly enough, it works great and never goes over about 55 C.
This has been good for lighting quite a few commercials and music videos already.
Since that project things have progressed:
First of all I had the heatsink machined out of a solid block of aluminum. (That was pretty expensive)
Also made the whole thing a bit smaller. The first one was 12"x12" but this one is 9"x12" instead. The LEDs are a bit closer together.
Also I redesigned the power converter. Now it will take input 12-48 volt DC, 94 to 97 percent efficiency. It is also microprocessor controlled - PIC24H 16 bit controller running at 40 MHz.
Also it has some different modes. Now the MCU can accurately control the color so instead of just two pots, one for each color, it's possible to have one pot controlling the mix, and the other pot controlling the overall intensity. And there's a temp sensor to keep everything nice and toasty. Oh wait I also implemented master/slave so you could chain a few of the lights together and make them all do the same thing at the same time without need for a lighting board.
And I even put a DMX interface on it. The DMX interface has RDM so there aren't any DIP switches.
Finally I found lenses that would fit the COB arrays. Had a Delrin holder machined for them. They only focus the light in one direction. But that's OK, it's pretty bright already, although it hasn't really got a lot of throw. My favorites are the medium lenses. They have 30 degree vertical spread x 140 degree horizontal, with about 60 foot-candles at 10 feet.