The Line Tracking Sensor for Arduino can detect the white lines in the black background and black lines in the white background. If Line Tracking Sensor detects black color, the signal line (DO) of the sensor is HIGH, at the same time the LED (blue) on the sensor lights up. If Line Tracking Sensor detect white color, the signal line (DO) goes LOW. With the potentiometer, you can adjust the sensitivity of the Line Tracking sensor and the distance to a line. The best distance between objects such as ground and the sensor is 1-3 cm.