The Soil Lamp by Marieke Staps runs on mud. The lamp has copper and zinc strips coming out from the bottom of it and uses the soil as an electrolyte to power the LED light (just like a potato battery you created in grade school). The soil does need occasional waterings to keep it muddy so the reactions can continue to light the lamp up but beyond that, it should be maintenance free. This is the type of light that would be perfect for lighting up a shady path or garden area- just stick it in the soil and that’s it. Oddly, it doesn’t appear to have an on/off switch.