A diode made from a semiconductor can generate electricity in the presence of light. Instructables user nevdull shows how to generate a modest amount of power by arranging four 1N4148 diodes in parallel.
Go ahead and dig out a few diodes from your tacklebox, toolbox, bead drawer, or whatever you keep all your electronic goodies in and put them in parallel. Connect your voltmeter to either side and take a reading in ambient light. I get about 4-5mV in ambient light.
Next, grab your maglight and while still taking a reading shine a focused beam on the diodes and see what your voltmeter says. In my configuration using the diodes I had at hand, I was able to get more than 100mV from four diodes. That’s not too shabby, especially if you’re shuffling that voltage off to a capacitor to either save for later or to build up a larger charge to do something more useful, like light an LED (yeah, like that’s more useful) or run your garbage disposal.
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