Photoresistors are variable resistors, which react to the number of photons present in the environment. They are most reactive to frequencies of light with sensitivity in the region of 500-600 nanometers (nm). You can purchase photocells here.

You can put a photoresistor in a tube to allow it to be even more sensitive to shadow. A nice article on photocells can be found here.

Hooking up a photo sensor with a resistor to the Arduino.

If you did not want to have to build your own some come with the 10 K Ohm resistor as already part of the board.

Keyes KY-018 Photosensitive Resistance Sensor Module For Arduino.

As with all photosensors they can be used for wide pan sensing to sense shadows. We see them in solar garden lights - lawn detectors - clocks- musical gift boxes - mini-night lights - light switching toys on as well as a variety of light control applications: Working voltage: 5v
PCB size: 1.5 x 1.9cm.

Keyes Photo resistor module.

The code for the analog input for the photoresistor is the same as that for the potentiometer.

Copyright Ken Rinaldo