Step 1: Materials
-20 latex balloons
-20 3v coin cell batteries
I used red LEDs and pink balloons, but any colours will do.
Step 2: Assembling the LEDs
First trim down the anode ( + long lead) and cathode ( - short lead) so that the length of either lead is shorter than the diameter of the battery.
After the leads have been trimmed down, wrap a strip of paper around the cathode lead of the LED.
Then, insert the battery between the leads of the LED with the strip of paper. I used scotch tape to hold everything together, but most any tape will do.
Step 3: Assembling the balloons
I doubled over strips of tape t stick the balloons together side by side. The reason I had popped a balloon was that I pulled the tape on the balloon and the latex ripped. As a precaution I also tied the balloon strings together as a stress relief for the taped areas.