Basically, it is a standard CdS sensor which has low resistance in bright light and high resistance in darkness. Since it carries the current from the +5 supply to ground, the analog sensor has a value of about 0 in bright light, and about 255 in darkness.
The Inventors Guide on the item is
here.
If you mean the specific characteristics of the CdS device used in the Vex product, I don't have that info, but I am sure Vex Labs would answer that in their
forum.
Don