This configuration will let the robot sense light, or lack of light, on the left and right. This is most useful to make a robot that follows light or keeps to the shadows.
Basic Robot With Reflection Sensors
By adding two LEDs to the basic robot, we can now detect if light is reflecting off of a near by object. This will allow us to make a robot that can follow a black line on a white surface, avoid walls, and stop before it goes over the edge of a table.