Abstract: An obstruction detection system includes emitters, a sensor, and obstruction detection circuitry. The emitters mounted along the top of an opening radiate a plane of light toward the floor. The plane of light intersects the floor and creates a floorline at the intersection of the plane of light and the floor. The plane of light also intersects the door edge and creates a door edge line at the intersection of the door edge and the plane of light. A sensor, located outside the plane of light, monitors the opening so that the presence of the obstruction can be detected from a change in a received light pattern of the floorline, the door edge line, and from reflections from an obstruction in the plane of light. The sensor provides an output signal in response to the received light pattern to a means for analyzing said sensor output signal for obstruction detection.