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What capacitor to use for a flashlight?

I googled to get no help. I want to make a shake flashlight and I want it to run off a capacitor not a battery but I don't know how to figure out which one to use. I came across this http://homeenergypros.lbl.gov/profiles/blogs/correctly-sizing-a-capacitor but that's the closest I've came to anything.

If I were to have 5 volts at 30 amps just for example, how do I calculate what I need? I can identify the capacitors and do the rest myself I just need to figure out how to calculate the correct one for the job.

capacitors discharge their charge very quickly so it would not be very useful in a flashlight 

Capacitors are usually used to up volt a system, they take a low constant flow of energy and store it (much like a dam) then when the system needs the power it releases the charge all at once (dam breaks) and then starts the sequence over again.

For your needs you probably want to look into some kind of dynamo maybe or something more mechanical that can capture the kinetic energy of shaking then release it slowly over a period of time.

http://www.youtube.com/watch?v=tHg51GOzCXU

He used a capacitor and it was powered for ten minutes

http://www.vat19.com/dvds/nightstar-forever-flashlight-shake-flashlight.cfm

A popular shake flashlight with no batteries. 

Many of these "never replace bulb and no batteries" shake flashlights work well. I understand a capacitor doesn't hold much charge and can dump it quickly so how do these work?

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