Line trackers are useful tools in autonomous control for detecting changes in light. They work by shining an infrared light onto a surface. An sensor then detects the intensity of the light that bounces back, and translates it into a numerical value. Since darker colors absorb more light than lighter colors, the data value will be different depending on the shade. Normally, lighter colors will have a lower value, while darker colors will have a higher value. Line trackers are analog sensors, which gives them a higher data range compared with digital sensors. The data range for a line tracker is between 0 and 4095.
The main use for line trackers, as stated in the name, is to track lines. Having a light colored line on a dark colored surface or a dark colored line on a light surface is recommended, as the bigger the contrast between colors, the easier it is for the sensor to differentiate between the two. In most VEX competitions, white reflective tape is set in various places on dark gray tiles, which makes it easy for the line tracker. The most common setup to following a line is to use three line trackers as shown in the image above. When the middle line tracker sees the tape, it knows that it is on the right path, and the robot will continue to advance forward. However, if either the left or right sensor detects the tape, the robot will slightly turn in the opposite direction until the middle sensor is the only one that sees the tape.
VEX Sensors and How to Use Them 
Line trackers can definitely be useful in robotics. I’ve seen them work really well in autonomous programs. I know this is FIRST related not VEX, but one of the teams on the first alliance at the Northern Lights regional actually tracked lines on the carpet, and they had a really successful autonomous program. It’s awesome that you’re explaining how different VEX sensors work. It’s some of the small things that people might forget about that end up being really helpful.
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