This is a very small light sensor .
It is called light sensor or photocell or LDR (light dependent sensor) or photo-resistor.
A photocell changes resistance depending on the amount of light it is exposed to.
These little sensors make great ambient light triggers (when light in the room turns on, do something).
Features
- Light resistance : ~1k Ohm
- Dark resistance : ~10k Ohm
- Max voltage : 150V
- Max power: 200mW
