Current flows in a light detection device when collide with its pn junction.

The light detection device is also called photodetector. It transforms any natural or artificial light source it encounters into sound.
Current flows in a light detection device when light collide with its pn junction.
When light falls on the junction, a reverse current flows which is proportional to the illuminance. The linear response to light makes it an element in useful photodetectors for some applications. It is also used as the active element in light-activated switches.

Some type of thing that was invisible