Was browsing the dollar store and picked up a solar powered daisy. Plastic flower that waves around powered by light.
Has two small solar cells charging an electrolytic cap. Disappears under a blob of epoxy. Out the other side comes a coil that sits under the magnet on the daisy shaft.
Runs on surprisingly low light level. I don't have a high impedance measurement device or the inclination to measure it, but it appears that the cap charges until it reaches a threshold and dumps into the coil. Lower light level increases the time between dumps. The coil has a lot of turns, so stepping up the voltage will take more turns than I'm willing to wind. I just stuck it in the window. I always wanted a plant...
Most impressive thing is that it has about 8 molded plastic parts, two solar cells, a circuit board with a chip, an electrolytic, a coil of wire and a magnet. Comes in a bubble pack with a cardboard insert. It must pass through at least three levels of distribution channel and get shipped from China then trucked to the vendor. And they can sell it to me for a buck!!!
The donut I bought to fuel the bike ride home with it cost more than the daisy.