Laser is the abbreviation for Light Amplification by Stimulated Emission of Radiation. When the laser speed gun is activated, it sends out a very short burst of infra red light to the target vehicle. The light beam reflects back to the laser gun when it hits the target vehicle. The number of nanoseconds taken by the light to travel to the target vehicle and reflect back is divided by 2 to determine the distance of the targeted vehicle. A laser gun can send out over a thousand bursts of infra red lights per second. The laser gun calculates the speed by comparing the difference in the distances between the bursts. The accuracy of a laser speed gun can be very high. In the US, the Marksman LTI 20.20 is the most commons laser gun used by the police to check speed. The Marksman LTI 20.20 has a beam width of 2 feet at a distance of 1300 feet. The manufacturer claims the gun has an accuracy of 1 mph for speeds up to 60 mph and for speeds over 60 mph, the accuracy is within 3%.
Despite tall claims by the police and manufacturers, laser guns have their own weaknesses. The unusual beam intensity distribution can affect the aim – the light beam can strike and reflect from another vehicle which is close to the target vehicle. Clouds, rain, fog and other weather conditions can severely affect the accuracy of a laser gun. A laser gun cannot be used through a windshield. The laser gun must be used while it is stationary. The surface of the target vehicle can also influence the accuracy of a laser gun. For a laser gun to give an accurate reading, the light beam must hit the target vehicle and reflect back. If the target vehicle’s surface is not reflective, the reading will not be accurate.
A laser gun like all other machines requires proper maintenance. Poor maintenance can affect the laser gun. For proper functioning, a laser gun must be calibrated before use. To properly calibrate a laser gun, the self test button must be activated and the result should be 18.104.22.168. Next the gun must be used against a stationery vehicle and the resultant speed should be 0 mph. The sight and audio tones must be tested by sweeping across a telephone pole.
If you have been issued a speeding ticket based on a laser gun reading, consult with an experienced driving law attorney. The attorney can challenge the accuracy and maintenance of the laser gun and have the charges against you dropped.