The light sensor is made up of primarily of LDR and opamp:
[caption id="attachment_382" align="aligncenter" width="319"]
The Grove light sensor (image: seeed studio)[/caption]"LDR" stands for light dependent resistor (in above schematic, it is marked as "LIGHT") as the name suggests, it is made up of a material that changes it resistance depending on the intensity of the ambient light.
