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The Pololu QTRX-HD-09RC Reflectance Sensor Array is a 9-sensor array of infrared (IR) reflectance sensors designed to detect ambient light levels, reflectance levels of an object, and the angle of the light source relative to the sensor array. The array is an upgrade to the original QTR-3A version, offering a greater range of detection with improved performance and handling of counter-light reflections. It is a rugged, low-priced option that can be used in a variety of applications, including line and edge following robots, color recognition, and obstacle avoidance. The array can measure ambient light levels and then calculate the exact value of each color relative to the light source. It is ideal for robotics applications as it can detect up to nine individual IR reflection points in close proximity.