The Latro (which comes to us by way of Treehugger) requires sun, which can be provided by leaving the device (which really looks more like a huge beaker full of green goo than an actual lamp) outside during the day–or presumably, in a sunny window. While the algae is photosynthesizing away, it will also be charging up a battery, which then releases light, according to the designer “within the hours of darkness” (we assume automatically).