They only take a few minutes to make, so you can build a bunch of them quickly, and they come in many colors. These LED strips are designed to be run off of 12 volts, but you can use a 9 volt battery, and it all fits easily in a pumpkin. The strips are parallel, so you can use any length you want, and no resistors etc. are required.
Step 1: Materials
1) LED Strips - you can get these in many places like the below:
- Adafruit - there is also a nice tutorial on soldering leads here
- HobbyPartz - lots of color choices here
These strips are waterproof and they have adhesive tape on the back.
2) 9v battery clip
3) heat shrink tubing (~1/4") - about 1/2" long
Step 2: Assembly
For the 9v battery lead, trim the wires down to short lengths - about 1/8" long.
Use a soldering iron to tin the pads on one end of the LED strip, and tin the 9v battery clip leads. Then solder the leads to the pads.
Test the LEDs, and when they are working use the heat shrink tubing to protect the connection. We were able to slip it right over the LEDs
Step 3: Installation and Improvements
For the TeleToyland Sandbox 2 project, we made them controllable over the Internet using and Arduino controller - you could do the same with these. There are also several Instructables on Arduino controlled pumpkin lighting.