Line following using the Color Sensor

When we are using the Color Sensor in Reflected Light Intensity mode, the sensor emits light and the robot measures the intensity of the reflected light. The brightness of the red LED in the sensor is a constant, but the intensity of the reflection will depend on the reflectivity of the surface, the angle of the sensor relative to the surface, and the distance of the sensor from the surface. If you shine the sensor at a surface, you will notice that a circle of light is generated. As you change the height of the sensor, the diameter of this circle will change because the light emitted from the LED diverges in a cone. As you increase the height, the size of the circle gets larger and the reflected intensity gets smaller. You might think you want the sensor to be as close as possible to the surface. Because there is a finite distance between the LED and the photo diode (which collects the light) of about 5.5 mm, it puts a constraint on the minimum diameter...