The QTR-HD-03A reflectance sensor array is part of the QTR HD line of reflective optical sensors from Pololu. The sensor array consists of three closely spaced, light-sensing elements. This arrangement allows it to detect both the presence and the position of a reflecting surface in the detected area. It can also be used to monitor changes in intensity, as well as making it possible to detect motion. Designed to measure light, the sensor features a wide sensing range and can detect intensities from 0% up to 100%. The unit comes with a white LED and receiver, allowing for sensors to be placed anywhere a white surface is present for optical measurements. Applications for the QTR-HD-03A reflectance sensor array include robotics, line-following robots, proximity sensing, color recognition and many more.