How motion detectors work
Motion
detectors are small electronic eyes that detect infrared waves—heat
waves that radiate from moving objects. When the detector senses an
object moving across its field of view—especially warmer objects such
as people, animals and cars—it electronically turns on the lights. The
light stays on anywhere from 1 to 20 minutes, depending on how you
preset the timer. Then the detector automatically shuts the light off
unless it continues to sense movement. A photocell deactivates the
light during daylight hours. Most motion detectors have a semicircular
field of view of up to 240 degrees and a distance range, adjustable on
most detectors, that extends to 70 ft. or more. The detector will react
to the movement of your dog, an approaching person, a passing car or
sometimes even wind-blown leaves.
Nuisance “trips,” such as blowing leaves or a passing car, can fool
the detector and turn the lights on when you don’t want them. These can
be annoying to both you and your neighbors, and in fact, some
homeowners won’t install motion detector lights for this reason.
However, you can solve most unwanted switching-on by adjusting the
distance-range setting and by carefully aiming the sensor to limit its
field of view. You can also narrow the field of view even more by
applying tape to the sensor, as shown in Photo 7. If nuisance trips
concern you, be sure to buy a light that has an adjustable
distance/range setting, and an aimable detector unit as shown in Fig.
A, Nos. 1 and 3.
Motion detectors allow you to operate the light in the conventional, manual way, usually by flipping a switch
off for a second, then back on. This allows you to keep the light on
at night when you want to, even when there’s no motion. By double
flipping a second time, you return to automatic.
Motion detector and light styles
Figure A: Motion detector and light styles
There are many motion detector and light styles to choose from.
Where to put them
For
best effectiveness, position motion detector sensors to cover the
walks leading to your front and back doors and the driveway (see lead
illustration). That way the lights will come on when you come home at
night. You can also use them to light up decks, patios and any
potentially hazardous locations such as around stairways and swimming
pools.
If improved security is a priority, position the lights to cover all
the approaches to your house, including fence gates, the patio door,
the darker areas of your yard, and around trees and bushes. Good
lighting can’t guarantee security, of course, but it’s one of the best
low-cost ways to get unwanted intruders to back away.
Ideally, it’s best to mount motion detector lights 6 to 10 ft. above
the ground and position them so that most movement will occur across
the sensitivity zone rather than directly toward the detector.
Obviously you can’t always do that if you use existing light locations.
One solution is to buy a remote motion sensor unit that you can mount
some distance away from the light itself (Fig. A, #3). The wires
connecting them to the light are low voltage and may not be dangerous, so you don’t have to enclose them in metal or plastic conduit.
How to install motion detector lights, step-by-step
1 of 7
Photo 1: Shut of the electricity
Turn off the power to the fixture at the main panel, then test the wires to make sure the current is off. Rub one lead of a voltage tester (from hardware stores or home centers) against the ground wire
and rub the other lead first against the hot wire (black), then the
neutral wire (white). If the tester lights up in either case, the power
is still on. Shut off the correct circuit at the main panel.
Have the necessary tools for this project lined up before you start—you’ll save time and frustration.
Required Materials for this Project
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.
Motion detector light
Electrical box, remodeling type
Wire connectors
Clear silicone caulk
Electricians tape, plastic
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