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The inspiration is from gravity lights, which has been shown in figure, and it is designed by a team from Kenya and can be used in countries of the third world or in developing countries. Compared with kerosene lamps, gravity lamps are more energy-saving and environmentally friendly. For the selection of raw materials, gravity lamps are not as harsh as kerosene lamps. Only enough stones are needed, and such conditions are easily met in the third world. And they are a substitute for kerosene lamps. First fill the bag with gravel, about 20 pounds, to get enough weight. Place the bag high so that it slowly descends, and the drop time will be controlled for about 25 minutes. The descending weight drives the generator to operate to supply power to the load. The load can be an LED light. The energy generated by the falling weight can maintain the LED lamp for 25 minutes.