I am specifically asking about watches that advertise that they need only light to work. Example:[Seiko Watches](https://www.longislandwatch.com/Seiko_Solar_Watches_s/1966.htm)
There is no visible solar panels in them? Can’t this technology be used for other types of clocks like wall clocks?
In: Technology
The watch face in part a solar panel. You can see a solar panel part quite clear on the [first clock](https://www.longislandwatch.com/Seiko_SNE435_Solar_Dive_Watch_p/sne435.htm) where the solar cell in the center almost black part of the clock face. It is likely a lot more visible if you would hold it in you hand and you could see the difference in reflection when you tilt it.
The clock with white faces the white surface is either semi transparent or is a some new models that reflect all visible light and the solar cell only uses IR light.
The solar cell on a clock do not need to be large as the energy use of a clock is very low, there is a reason that clocks work for years with a small battery. You can find a [solar clock teardown here](https://fccid.io/BKMAP012/Internal-Photos/04-Short-Term-Confidential-Internal-Photo-3475471)
You can certainly build solar powered wall clock with hidden solar cells because the are made. One of the first on a image search for “solar powered wall clock” was [this](https://global.rakuten.com/en/store/auc-cecicela/item/4my799qe06/) with hidden solar cells.
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