For something completely different, check out this project by Arduino forum member "moryde". They have used the sending and receiving of a blinking LED to transmit data between two Arduino boards at a sedate pace, in a method similar to that used by maritime folk. It's still in development, but could be the framework for slow but simple data transmission across two very different types of equipment. The project is demonstrated in the following video:
If you're looking to detect changes in light levels, don't fool about with irregular light-dependent resistors. Instead use our LIGHT: light sensor module with the TEMT6000 light sensor which gives consistent and repeatable readings even between different units. Simple to use and versatile for many applications. For more information and to order,click here.