Here comes DFRobot's new Analog Ambient Light Sensor for Arduino or
Raspberry Pi, with a brand new design and much more convenient to use. This sensor helps you to detect the light density and reflect the analog voltage signal back to the Arduino controller. You can set the threshold of voltage level to trigger other units on the Arduino project.
We also use the enviromental PT550 light sensor and it is more sensitive to light than a normal one.