The yellow spring is in permanent contact with the base of the bulb and the positive terminal of the batteries. The red wire is in permanent contact with socket of the bulb. When not in use, the weight of the batteries compresses the spring and shuts off the contact with the wire and the batteries negative terminal. When the light is thrown into the water, it floats in vertical position immediately, thanks to its specific shape. The batteries slide down in the tube and, with their weight, create the contact with the wire connected to the bulb. Will shine for 2 hours and contains 5 batteries.