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- #61
Laser gun
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The latest addition to the police's speed detection arsenal is the laser speed gun, otherwise known as Lidar (Laser Infra-red Detection And Ranging).
Laser guns do not use the Doppler Effect like radar guns. Instead, to measure a vehicle's speed, they time how long pulses of infra-red light take to travel from the gun to the vehicle it is being fired at and back again. The light reflects off any flat surface on the vehicle. By sending out a series of infra-red pulses at short intervals and comparing the distance the vehicle has travelled between times, the gun very accurately determines the vehicle's speed.
Laser speed guns are more expensive than radar models. However, their one big advantage (from a police point of view) is that they can be aimed with far greater precision. The light beam from a laser gun is much narrower than a radar beam, so laser guns are much less subject to interference from other vehicles or roadside furniture.
It's not all bad news for motorists, however. There are some factors which mean laser devices may not be as accurate as the authorities would like to believe.
They must be aimed at a vehicle very accurately, requiring the skills of a marksman. The devices are also more complex than radar guns, leaving more room for human error. Operators therefore require more training, and lack of this may be sufficient to cast doubt on any conviction.
Laser devices cannot be used through glass, as this will distort the readings. If an officer has 'lasered' you through his patrol car window, therefore, the case should be thrown out of court.
Lasers cannot be used properly in rain, snow, fog or other conditions of reduced visibility. If the operator cannot see your car clearly, he will not be able to aim the gun precisely enough. Note that lasers CAN be used at night, however, unlike radar guns.
Like radar guns, lasers must be professionally calibrated at least once a year and a certificate issued. And again like radar guns, both before and after they are used for any tour of duty, they should be checked against a police vehicle fitted with a certified calibrated speedometer at a speed compatible with the sites where they will be used.
If you are stopped by a police officer using a laser speed gun, therefore, it is very important to note carefully all the circumstances applying at the time to see if any of them may provide grounds for appeal (we will go into more detail about this a little later). However, there are some precautionary measures you can take to reduce the risk of detection in the first place.
Go for a sleek, low-slung, aerodynamic car. Such cars offer fewer flat surfaces for a police officer to aim a laser at.
Choose a dark coloured vehicle, e.g. black, dark blue or dark green. Such colours are harder to target, especially in overcast conditions, and do not reflect the laser light as well.
Tilt your numberplate so that it is pointing upwards or downwards. Many operators aim at the numberplate as it reflects better than a vehicle's bodywork, but if it is tilted away the beam will be deflected into the air or onto the road.
Powerful driving lights can also help you to avoid detection. Operators are told not to point their lasers at bright lights, as this can burn out their circuitry!
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The latest addition to the police's speed detection arsenal is the laser speed gun, otherwise known as Lidar (Laser Infra-red Detection And Ranging).
Laser guns do not use the Doppler Effect like radar guns. Instead, to measure a vehicle's speed, they time how long pulses of infra-red light take to travel from the gun to the vehicle it is being fired at and back again. The light reflects off any flat surface on the vehicle. By sending out a series of infra-red pulses at short intervals and comparing the distance the vehicle has travelled between times, the gun very accurately determines the vehicle's speed.
Laser speed guns are more expensive than radar models. However, their one big advantage (from a police point of view) is that they can be aimed with far greater precision. The light beam from a laser gun is much narrower than a radar beam, so laser guns are much less subject to interference from other vehicles or roadside furniture.
It's not all bad news for motorists, however. There are some factors which mean laser devices may not be as accurate as the authorities would like to believe.
They must be aimed at a vehicle very accurately, requiring the skills of a marksman. The devices are also more complex than radar guns, leaving more room for human error. Operators therefore require more training, and lack of this may be sufficient to cast doubt on any conviction.
Laser devices cannot be used through glass, as this will distort the readings. If an officer has 'lasered' you through his patrol car window, therefore, the case should be thrown out of court.
Lasers cannot be used properly in rain, snow, fog or other conditions of reduced visibility. If the operator cannot see your car clearly, he will not be able to aim the gun precisely enough. Note that lasers CAN be used at night, however, unlike radar guns.
Like radar guns, lasers must be professionally calibrated at least once a year and a certificate issued. And again like radar guns, both before and after they are used for any tour of duty, they should be checked against a police vehicle fitted with a certified calibrated speedometer at a speed compatible with the sites where they will be used.
If you are stopped by a police officer using a laser speed gun, therefore, it is very important to note carefully all the circumstances applying at the time to see if any of them may provide grounds for appeal (we will go into more detail about this a little later). However, there are some precautionary measures you can take to reduce the risk of detection in the first place.
Go for a sleek, low-slung, aerodynamic car. Such cars offer fewer flat surfaces for a police officer to aim a laser at.
Choose a dark coloured vehicle, e.g. black, dark blue or dark green. Such colours are harder to target, especially in overcast conditions, and do not reflect the laser light as well.
Tilt your numberplate so that it is pointing upwards or downwards. Many operators aim at the numberplate as it reflects better than a vehicle's bodywork, but if it is tilted away the beam will be deflected into the air or onto the road.
Powerful driving lights can also help you to avoid detection. Operators are told not to point their lasers at bright lights, as this can burn out their circuitry!