WHAT YOU SHOULD KNOW ABOUT LASER
AND LASER DETECTORS
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
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.