Dutch designer Marieke Staps has built a lamp with the LEDs powered by soil. She writes:
"Free and environmentally friendly energy forever and ever. The lamp runs on mud. The metabolism of biological life produces enough electricity to keep an LED lamp burning. The mud is enclosed in various cells. These cells contain copper and zinc that conduct the electricity. The more cells there are , the more electricity they generate. This technique offers a wealth of possibilities. The only thing the lamp needs is a splash of water every now and then."