A Photo Cell, also known as a CdS Photoresistor, is a type of light-sensitive electronic component used to detect and measure light levels in various applications. It consists of a semiconductor material, typically cadmium sulfide (CdS), whose resistance changes in response to incident light. As the light intensity on the photoresistor changes, its resistance alters, leading to a corresponding change in electrical output. CdS Photoresistors are commonly used in light detection circuits, camera exposure controls, streetlights, and ambient light sensing applications in electronic devices. Generally, CdS Photoresistors are known for being relatively inexpensive compared to other light sensors. When purchasing the photo cells, determine the required sensitivity range and resistance characteristics based on the light levels you need to detect. Additionally, verify the photoresistor's compatibility with your circuit's voltage and current requirements.