I remember wondering years ago if it were possible to design a lamp that you would feed and water like a houseplant. Well, apparently, it is, and designer Mike Thompson has done it (conceptually, anyway). He calls it Latro. There’s more info over at Inhabitat:

The lamp is made possible thanks to a recent discovery made by researchers at the universities of Yansei and Stanford. The researchers found that a tiny electrical current can be extracted from algae during photosynthesis. The Latro Lamp features a battery that stores energy generated by the algae throughout the day and a light sensor that controls the lamp’s intensity, preventing the algae from becoming malnourished. Thompson believes this discovery could lead to an algae revolution: “As advances in nanotechnology lead to increasingly energy efficient products, plant life such as algae will become attractive sources for tapping energy,” he says.

I’m guessing the electrical potential used to charge the battery during the day would be generated between the top and bottom of the algal layer and is ultimately due to a gravity-induced concentration gradient of some kind of metabolite in the broth.