The LED will stay on for about 2 hours, which is when the paper naturally dries out. To light the LED just reapply the salt water. Depending on the ab...
Here are two design variations on a traditional voltaic cell. Both designs are solder less and easy to construct from common household items. The flower and lamp are basically giant paper batteries with the wetted paper acting as a salt bridge between the wires.
Step 1: The Frame
I used the cardboard from a box of soda as the base of the lamp and construction paper for the shade. After making 6 pairs of fairly evenly spaced holes in the base I rolled the paper and marked where the holes lined up- in this example they were an inch apart. It's important that the wetted paper containing the wires doesn't touch it's neighbor or the current won't know where to flow. Cut v-shaped pieces out near the bottom where the shade connects to the base to prevent that from happening.