Solar-powered watches

Watches which draw their power from light energy using solar cells are called solar-powered watches (or solar watches/clocks, Solar-cell watches/clocks). 
A Solar-powered watch is equipped with a solar cell, which converts light energy into electrical energy. The electrical energy generated by the solar cell is stored in the rechargeable battery to power the watch.
A Solar-powered watch can generate enough power to run itself from not only sunlight but also from fluorescent light and a slight ray of light.

The solar energy falling on earth, which is 150 million kilometers away from the sun, is estimated at approximately 1.77 x 1014kW when converted to electrical energy. The solar energy received in a single hour on earth is said to be equivalent to the sum of the world's energy consumption of an entire year. Solar energy generation aims to utilize this enormous amount of light energy by converting it into electrical energy.

The solar energy generation system emits no environmental pollutants, and generates no oscillation or noise because it has no moving parts. 
It is literally a non-polluting, clean energy transmission method.

Solar cells take advantage of the photovoltaic effect in semiconductors to convert light to electricity. Solar cells are power generating devices, which consist of two different kinds of semiconductors, p-type and n-type semiconductors placed in layers.
Solar cells use silicon or other various compounds as their semiconductor materials. Currently, silicon is most commonly used. Silicon can come in various forms depending on the deposition methods: single-crystalline, polycrystalline, or amorphous. Amorphous silicon can efficiently generate electrical power absorbing even a slight artificial light source such as a fluorescent lamp as well as sunlight.