According to Staps' site, the lamp only needs a splash of water once in a while to keep the LED lit up. Cells containing copper and zinc (and mud) power the lamp.
Anyone who's more, perhaps, biologically savvy want to explain to us how this works? We're assuming there's some sort of chemical reaction in the soil... We read somewhere that the cells in this lamp probably will need replacing over the life of the lamp. But if power can be harnessed from mud, then it does seem as if the possibilities are endless. In any case, this is an earth-friendly and interesting concept!
Photo via mariekestaps.nl