I built the flasher circuit from Dave Johnson's website, See URL
I then connected it to a 3V photovoltaic cell and a 1N4148 to prevent the current from going back into the photocell, and a 6800 uF capacitor to store the current generated by the light. I put the photocell directly under a light bulb, and it works fine, and it keeps working for less than a minute when the light is turned off. So now I need a lot bigger capacitor, something that will run it for a coupla hours.
I'm thinking that it would work good using a pair of 1 F, 2.0V supercaps in series, charged by the photocell.
I bought a Forever Flashlight, the one that has a single white LED, with a magnet and coil in the barrel that charges up a supercap when it is shaken. It works, but I'm disappointed in the light output. The instructions say to shake it for 90 seconds, but even longer than that gives the LED only a few mA, not a really decent amount. It has a lens to concentrate the LED's light, so it's better than just the bare LED alone. Obviously it's meant to be used for situations where a regular flashlight might not be working, like in an emergency/earthquake preparedness kit. The body of the flashlight is clear plastic so I can see the parts inside, and there's a supercap in there, but the plastic is too thick to see the value, which is blurred.
So I'm wondering if I should order a couple of these supercaps. The solar cell is rated for 3V at 40 mA, see the SPL-60 on All Electronics website,