The Light Sensor module base on a Light Dependent Resistor (LDR). Typically, the resistance of the LDR or Photoresistor will decrease when the ambient light intensity increases. This means that the output signal from this module will be HIGH in bright light, and LOW in the dark.
For Light Sensor has two outputs:
AO - analog output, real-time output voltage signal of the Photoresistor
DO - when the light intensity reaches a certain threshold, the output high and low signal. The threshold-sensitivity can be adjusted via potentiometer on the sensor