12
What you should know about laser
How Traffic Laser Works
To measure speed, traffic laser sends out a beam of pulsed
infrared light. The beam is tightly focused: at a range of
1000 feet, it’s only about four feet wide.
Infrared is invisible to the naked eye — the operator can’t
see it and neither can you. But it is light and it behaves
accordingly. It travels in straight lines. And it’s easily
reflected.
Traffic laser works as a rangefinder. It sends a pulse, then
waits for the reflection from the target car. From the time
needed for the pulse to go out and back, and from the speed
of light, it calculates distances to the car. These pulses are
sent frequently, up to 500 times a second. The changing
distance to the target over time is speed.
Laser can’t see over hills or through opaque objects. The
laser beam must hit your car directly, line-of-sight from the
laser gun, to measure speed. Under ideal conditions, it can
read speed in less than one second.
The pencil beam means that, in operation, laser is very
different from radar. Radar cannot single out one vehicle in
a pack, so the speed reading is usually attributed to the
leader. The narrow laser beam reads only the vehicle it
strikes.
How Laser Detectors Work
A laser detector is an electronic sensor calibrated for the
infrared wavelength used by traffic laser. It is extremely
sensitive. And it responds in as little as .006 seconds.
It should be mounted inside the car with the sensor facing
through the glass toward the laser. When the beam, or
scatter from the beam, strikes the detector, it warns
instantly.
