Q--You recently wrote about the value of energy-efficient lights, including those that are used to illuminate the outdoors. We're considering such a lamp for the outside of our home, but we have a question. Would the frequent on-off cycling of a motion sensor-driven lamp wear out the bulb of more energy-efficient lights? I know that it's not recommended to put a motion sensor on a fluorescent bulb.
A--The question you really bring up is which type of outdoor lamp produces the most energy-efficient light. The simple answer, says John Bachner, a spokesman for the National Lighting Bureau based in Silver Spring, Md., is "it depends."
For example, if you live in a rural area, or have a driveway that hardly anyone passes by, you could probably opt for a motion sensor lamp equipped with a not so energy-efficient incandescent bulb.
Why? If that bulb hardly ever comes on--say only once or twice for a few minutes each night--it will use little energy. Plus, incandescent bulbs are usually a lot less expensive than other types of more energy-efficient bulbs.
"A lot depends on how long the bulb stays on after it goes on," says Bachner. "If it's only a minute or so, you're using very little energy to light that driveway."
Let's say you live in the city, however, and you want a security light over your garage door in the alley. If it's a fairly busy alley with a lot of traffic, chances are that light would go on frequently during the night if triggered by a motion sensor.
That might not be the best scenario for a high-pressure sodium lamp, as the frequent on-off cycles would cause wear to the bulb.
Here, Bachner suggests there's still an opportunity for an energy-efficient high pressure sodium lamp but by eliminating the motion sensor.
Let the lamp run all night by hooking it up to a photo sensor cell, which will turn it on at dusk and off at dawn. You can accomplish the same goal with a timer.
"These types of lamps are so inexpensive to operate that leaving it on most of the night will cost you pennies," says Bachner. "And they provide a good deal of illumination for a low cost."
A high-pressure sodium lamp also has a reported lifespan of 24,000 hours (versus 2,000 for the typical incandescent bulb), which means you could get a good 10 years out of the bulb even if it runs some six to eight hours per night.
Of course, if you want the lamp to come on to surprise a potential burglar or just someone passing by your garage, you'll need the motion sensor option. Again, you should first estimate how many times that light would come on--and how long it would stay on--before you choose which type of light to install.
Got a question about home energy or home environmental issues? Write to Energy Q&A, Chicago Tribune, Your Place section, 435 N. Michigan Ave., 4th Floor, Chicago, Ill. 60611. Or you can e-mail energyqa@aol.com. Questions will be answered only through the column.