I recently stumbled across a lighted showerhead at a store that purports to operate solely through water - without an external power source. The lights also change color with the temperature of the water.

Putting aside questions regarding showering, would such an appliance pose the same problems on Yomtov/Shabbos as a standard light fixture? Or is there something unique about them that might permit their use as a light source?

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    No answer yet, but (to save others time, since I've spent a while Googling this) the LEDs use electricity generated by internal hydroelectric generators (that spin when the water runs) that power the LEDs. (Faulty ones can be rather noisy as the internal hydroelectric generators spin.) – Danny Schoemann May 4 '17 at 8:46
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    Probably a grama eino mitkavein on a Derabanan if @danny is right. Plus it's potentially more lenient because of havaara on Yom tov – Double AA May 4 '17 at 11:31
  • @DoubleAA I found some material on the various opinions regarding electricity and lights on Shabbos, none of it deals with LEDs and all of it assumes being plugged into the grid. – Isaac Kotlicky May 4 '17 at 11:40
  • So the question becomes: Can one turn a dynamo (like we had in the wheels of our bikes) on Shabbat. And can one cause one to be turned (and stopped) by opening the shower tap. – Danny Schoemann May 4 '17 at 11:46
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    @DannySchoemann Another question had the link I mentioned: daat.ac.il/daat/english/journal/broyde_1.htm The concern with generating electricity is one of havarah of the fuel used in generating, which isn't an issue here. Also not an issue are sparking switches, boneh, and (probably) havarah/bishul of internal components/filaments (which are "quenching" the same time as they're heating). Not really sure what's left, other than "we don't use lights." – Isaac Kotlicky May 4 '17 at 16:50

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