The Grove - Light sensor module uses GL5528 photoresistor(light dependent resistor) to detect the intensity of light in the environment. The resistance of photoresistor decreases when the intensity of light increases. A dual OpAmp chip LM358 on board produces voltage corresponding to intensity of light(i.e based on resistance value). The output signal from this module will be HIGH in bright light and LOW in the dark.
This module can be used to build a light controlled switch i.e switch off lights during day time and switch on lights during night time.