LIDAR

It has become common practice for police officers to use laser based speed measuring devices called LIDAR guns. LIDAR guns use short bursts of light (wavelength of which is 904 nm) to measure speed. It takes less than 0,5 s to make a speed reading. In this time LIDAR gun emmits 50 to 250 pulses of light. These pulses are reflected from target vehicle and LIDAR then calculates the speed based on change of distance in time.
Unlike radar guns, with LIDAR a policeman can target a single vehicle from a column of vehicles. Laser beam is very narrov, and has a diameter of only 25 cm at 100 m from gun.

Maximum measuering distance varies between different brands and models of LIDAR guns from 300 to 1500 meters (in ideal conditions).
Since LIDAR operates using pulses of light weather conditions affect it's ability to measure speed. Other limiting factor is reflectivity of target vehicle (better reflection means bigger range), thus police officers are trained to target at the most reflective surface on the vehicle - licence plate first. Other reflective surfaces are headlights, so it's necessary to protect them also.

Big impact on LIDAR performance has color and shape of targeted vehicle, and alo the distance. In ideal conditions range of LIDAR guns is about 1000 meters, but in real life situations it drops to about 300 meters.