You are looking at light reflected back towards the source. Alternately, you can at night use a flashlight held against your ear and pointed at the car. Stand back by at least 30 feet to see light returned at an angle close to straight back at the source. Some special materials absorb in the near IR and transmit in the visible and hence this test using visible light is not indicative that a special police-lidar countermeasure is working. The license plate is the strongest target on the front of the car.
Different States have a very large difference in the lidar return from the plates.
Colorado is one of the lowest, using retroreflective paint on only the letters and a thin border. The strongest reflection of the rear of the car is an array of little corner cubes in the red tail light cover. All cars have a hexagonal array in the plastic tail light covers. These are just like a bicycle reflectors. You can distinguish these retroreflectors from the tail light lens by the array pattern.