Re: DX first light
If you want a light/host to tinker with then DX is the place. Many of their lights can readily be taken apart, with minimal effort.... some just fall apart in your hands (LOL). FWIW, my track record with DX lights has been hit/miss, half of them arrived DOA or with flickering output problems.
For any DX light I do a complete part by part tear down upon arrival:
-Bust out my dremel + tools and completely dis-assemble
-Remove any glue or adhesive, a plastics-safe electronics part cleaner (aerosol can) is perfect for this
-Re-flow solder
-Re-epoxy LED slugs
-Flush out and re-Lubricate click switches with part cleaner and a light oil
-De-bur all sharp metal edges
-Clean and re-lube gaskets
-Re-grind + polish any metal to metal conductive junction through the body/bezel/switch pill
Now all my DX lights (clone-fire) have been as reliable as my better surefire, fenix, Romisen, eagletac...etc...
The only light I was unable to 100% revive was a DIY job for bigchelis. He had one light with a finicky click switch, where one out of every 3 button clicks would flicker. I tried everything to free up the mechanism... but couldn't. It still works, except for that one click out of 3... LOL. But then you just click it again to get the internal switch plunger to rotate over to one of the next 2 spots.
I dont think AA sized lights are ideal for DIY though, many require smaller diameter DC-DC boards, in the ~15.5mm diameter range. 17mm is the unwritten DX/KD standard for DC-DC boards. Sometimes you can get away with trimming/grinding the PCB down to size, but that can only go so far. But certainly emitter swaps are possible with lights this small. You should be aware that some of the better made DX lights are glued and/or potted so getting them apart is difficult. Especially the potted lights... akoray for example.
I generally prefer P60 compatible lights for mods... surefire, solarforce and all the clone-fire derivatives. They can be completely taken apart component by component, including the switch modules. If you mess up, you can always buy a new 17mm DC-DC board for $3 and a reflector pill/module for $2.
I think a great 2AA project would be one of these:
http://www.lighthound.com/Solarforc...-Switch-all-Black-Type-2-Anodized_p_2629.html
Add this:
http://www.lighthound.com/Solarforce-L2-Flashlight-Extension-Tube--L2-ECR_p_1625.html
Add this drop in
http://www.dealextreme.com/details.dx/sku.13658
And mod the DC-DC board with one of these (or something similar thats optimized for 2xAA)
http://www.dealextreme.com/details.dx/sku.4735
http://www.dealextreme.com/details.dx/sku.7882