Step 1: Gather the Parts
1 empty film canister (if you've gone all digital, go down to the local developer or camera store, they just throw these things away).
1 9vlt battery (doesn't even need to be a new one, I've found that ones run down to 7vlts will still light the LED's. So go replace the ones in your smoke detector, and use the old ones in your light.)
4 red LED's (I've used everything from the dimmer red "indicator" ones to the clear "Super-Ultra Bright") just make sure they are all the same.
A piece of packing foam, sponge, or packing "Peanut", about the size of the battery and about half as thick.
Step 2: Gather the Tools
Soldering iron and solder
hobby knife or scissors
paper, pencil, black and red marker or crayon (sorry not shown, but I figure you know what one looks like)
double-sticky tape or glue
needle nose pliers
wire cutters (or nail clippers)
Step 3: Make a Paper Pattern
Step 4: Insert the LED's
Take the LED's out, glue or tape the paper into the lid, and then using the pre-punched holes and the stick pin, poke holes in the lid. I use a cloth covered mouse pad to poke into instead of my fingers.
After all the holes are made, insert the LED's. Make sure to keep the short leads all on the same side, the short lead is the negative side, and we are going to wire the LED's in series, one long to one short. Make sure the leads go through the paper on the inside, this will come in handy later.
Step 5: Solder the LED's Together.
Put a touch of solder on the leads that are touching each other, make good solder joints, but don't get it too hot, or you'll melt the plastic and/or ruin the LED's. The paper helps protect the plastic from the heat, but make sure not to melt the edge, or it'll be hard to put the lid on.
While you are here, mark the shorter lead with a black marker , and the longer lead with a red marker (a "+" would be good too).
Step 6: Finishing Up
Bend the 2 long leads over, and then down against the lid. The loop at the end helps make better contact with the battery.
Cover this with the second disk you cut, making sure the leads are under the holes. Glue or tape this disk in place, and mark the battery terminals again. I like to use a dotted black line for the negative side, cause it kinda reminds me of the crimped negative terminal on the battery.
Cut the piece of foam to fit down one side of the battery, and then tape or glue it to the canister. Don't glue it to the battery, you might need to change it one day. Although the battery lasts for quite some time.
The foam piece keeps the battery from rattling around, and also from turning in the canister.