Do It Yourself: Motion-detecting lights great for security

Q. One of my neighbors has floodlights on his garage that turn on automatically when his car pulls into the driveway. He also has a nice porch light that does the same thing when someone approaches. Are these lights expensive and how do they work?

A. They are usually called motion-detecting lights but they actually detect infrared heat from objects that move into their field of view.

I think they are not only great for convenience and personal safety, but are first-rate security devices. I can’t imagine too many intruders waiting around if a light suddenly switches on when they approach a building and they are caught in a brightly illuminated area.

Any object that emits heat, including humans, animals and cars, can cause the lights to switch on, as long as the object moves into the wedge-shape field of view. The range of detection varies according to how the small detection unit is aimed, and larger objects such as cars will be detected farther away than humans or small animals. Many lights won’t detect objects more than 30 to 40 feet away.

The lights also shut off automatically, usually after a few minutes, but the on time can be pre-set on some lights.

Motion-detecting lights have been available for several decades, and a variety of styles are made. Prices are quite reasonable for such useful devices, and a two-lamp outdoor floodlight can be bought on the Internet for less than $15. The lights are sold at most home centers and hardware stores and are widely available on the Internet.

If there is an existing light that doesn’t detect motion, installation of a new light is fairly simple and instructions are usually included.

One drawback is that some lights can lose some of their detecting ability in hot weather, when the infrared heat from intruding objects is not strong enough to overcome the ambient temperature. I have had this problem with a porch light, which works beautifully in cooler weather.

If the light has a manual switch, it can be turned on and off manually like an ordinary light, but the switch must be reset afterward to restore automatic action.