Photo cell (CdS Photoresistor from Adafruit)

A very small light sensor. A photocell changes (also called a photodetector, photo resistor, CdS or photoconductive cell) 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).

Technical Description

CdS cells are little light sensors. As the squiggly face is exposed to more light, the resistance goes down. When its light, the resistance is about 5-10KΩ, when dark it goes up to 200KΩ.

Limitation

The linear relationship of the resistance and light level makes the sensor not very sensitive to changes in darken area, and also easily ‘max out’ where light is ample.

Skill

Noob (Basic)

Sample Sensor

Photo cell (CdS Photoresistor): https://www.adafruit.com/product/161.

GA1A1S202WP Log-Scale Analog Light Sensor: https://www.adafruit.com/product/1384.

Sample Exercise

https://learn.adafruit.com/photocells.

https://learn.adafruit.com/adafruit-ga1a12s202-log-scale-analog-light-sensor.