A solar cell is being turned into a light source by running electric current through it. Such ‘luminescence’ testing is performed routinely in ESA’s Solar Generator Laboratory, employed to detect cell defects—such as the cracks highlighted here.
![](https://scx1.b-cdn.net/csz/news/tmb/2019/1-lettherebeli.jpg)
Source:
https://phys.org/news/2019-09-image-solar-cell.html