I was able to leave the light on for about 6 hours straight without changing the 2 9V batteries. A word of caution, this costume is meant to be worn at night, the light is faint when seen in the daylight, see the 2nd pic what happens when a flash is used. I used 3 LEDs and stuck to the typical 350mA current specified by the manufacturer. Adding more current will simply burn them out faster so don't do that =)
Step 1: Materials
3-4 High Powered 1 Watt Green LED's - you can't use normal LED's, they simply aren't bright enough. The ones I purchased were: Luxeon Star LXHL-MM1D. Typically rated at 3.42 forward voltage and 350mA. I think their lumen rating is about 25 lm +/- 10%. A different datasheet (for the same product, weird right?) rated them at 50 lm. I don't have a tester, but I'll stick with the lower figure.
3021 BuckPuck - Purchase the one that fits the mA rating of your LEDs to save costs buying resistors. The buckpuck regulates the current to the LEDs, it provides a constant source of current regardless of the size/voltage of your battery pack.
-- You might be able to get away with a PowerPuck, a smaller version of the buckpuck, but the max input voltage is 8v. Only good enough for 2 LEDs...
Both can be found either at: Future Electronics (cheaper prices and more selection/product info, but slow shipping) or The LED Light (prices are slightly higher, but shipping was FAST [2day from NV to CA]).
Resistors - depends on which buckpuck you buy
Wire - to solder the LEDs together, and a longer length to run from the light, down the pole, and into your battery pack. This depends on your height!! I used around 24ga
Altoids Tin - To house everything
Electrical Tape or shrink wrap
RadioShack PCB (optional)
SPDT or SPST Switch - Rated at least the voltage of your battery pack
(2) 9V Battery clips - this also depends on the eventual battery pack
Thermal Paste - Helps in cooling. These suckers NEED this
Large Binder Clip - my ghetto heatsink
Smaller Binder Clip - my way of securing the light to the structure
GE Silicone - To waterproof the light
Optics for LEDs - Usually you'd purchase lens holders and lenses for the LEDs but since I wanted the light to be dispersed and not focused, I just left them naked. The viewing angle of the LEDs is 110°
3/16" Wood Dowels - or something lightweight and sturdy and cheap! These were 12" long in packs of 20 at my local craft store. Again, depends on your plans
Hot Glue & Gun - to assemble/hold the sticks together
I spent a lot of time on this. I ended up using the white parts of plastic bags and just fused them together. Cloth proved to be too grainy, not waterproof (in case it was a rainy Halloween), and a little heavier.
You'll need to find something to "wear" the plumbbob. It needs to be lightweight, and substantially sturdy. I tried using wire hanger, but it was too flimsy to hold the plumbbob at a sufficient height. I used a rod from window blinds (the one that opens/closes the slats)