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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.

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal



  1. Bruce Miller says:

    Can LED’s do the same? Recharge batteries in LED flashlights for example? Circuits please?

    1. Arno Brosi says:

      Yes,LEDs do the same.See YouTube video here:

  2. Bruce Miller says:

    Always include a schematic – leaves no doubts!

    1. The circuit is diodes in parallel

      1. Ian Fitzgerald says:

        Put them in series and you’ll get higher voltage at the expense of current.

  3. foobar64 says:

    Reblogged this on THE Blog.

  4. SkipF says:

    E^2/R=P… 100mv^2/10,000,000= 1nWATT (for FOUR diodes…)
    Find a MILLION nanoWATTs and you get a milliWATT.

  5. Jerry Carter says:

    It would be interesting to know the physics / chemistry behind this.

      1. Jerry Carter says:

        Thanks, SkipF! I’ll have to find time to watch the whole lecture – good stuff.

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