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What's wrong with my post light?

QuestionI have enjoyed your columns over the years but do not recall anyone asking this question. I bought two outside lights a couple of years ago but I have to keep replacing the bulbs. I have bought cheap, expensive, and heavy-duty lights; decorative lights for outdoor lighting; and the new energy-efficient gaslight with a 5-year warranty. The best I get with any incandescent light is a couple of months.

The energy-efficient bulbs I bought at the dollar store lasted approximately three months. I have looked for and found 120-volt to 130-volt bulbs and they gave me a little advantage, but not enough. I have even used electrical lube to improve conductivity. Almost every bulb has an exterior rating. Can you help?

AnswerIt's important to follow the fixture manufacturer's specifications for light bulb wattage, voltage, and bulb shape. The specific requirements for a fixture are normally listed on the box and/or on a sticker found around the socket. In most cases, exterior post lights or wall-mounted lantern fixtures will use a maximum 100-watt type A or type B medium-base lamp. Type A is a standard regular-shaped bulb design, and type B is the decorative design.

Light bulb manufacturers adhere to a standard industry rating for light bulb life called "rated life." A 60-watt incandescent bulb, for example, may have a rated life of 1,000 hours; however, not all bulbs of this type will last exactly that long. As explained by GE, the "rated life" is a measure of the median time in hours that it takes for a light bulb to burn out. This is the point in laboratory testing at which half the test bulbs have burned out and half the test bulbs continue to burn. That's why some light bulbs last longer than others—you just never know how long a bulb will really last.

However, while there are a variety of reasons for a light bulb to burn out quickly, I believe short bulb life in exterior fixtures is due to the simple fact that some light fixtures are designed with no venting. A tightly sealed fixture doesn't allow air to circulate to help dissipate heat buildup from the light bulb. I can only speak from my experience, but light bulbs used under these conditions that are left on 24/7 have a very short life.

I had a chance to look at your three-fixture post light and they are all as tight as a drum. With that in mind, here are a couple of recommendations for your fixture designs. First, reduce the heat emitted by regular incandescent and halogen light bulbs by installing lower watt bulbs—instead of 100 watts, use 60 watts.

If this doesn't work, try the post and lantern incandescent bulbs that have a bulb life over two years; post and lantern compact fluorescent bulbs with either a four-year or six-year bulb life (depending on the watt equivalent); or post and lantern halogen bulbs with a life expectancy of two years. Halogen bulbs can last two to three times longer than incandescent bulbs. Consider purchasing the light bulbs at a specialty lighting store.

Finally, alter your fixtures so they vent, easily accomplished by raising the fixture's roof. The roof is normally held in place by a couple of brass screws that go down through the roof and fasten into the frame underneath that holds the glass panels in place. Purchase nylon spacers and longer screws at a length that will allow the roof to be raised by 1/16 inch.

This 1/16-inch space around the fixture will allow heat from the bulb to escape, thus giving the bulb extra burning life. However, too small an overhang on the fixture's roof may allow water to enter the fixture, so drill two drain holes in the bottom of the housing. Before reconfiguring your UL-listed fixtures, check with the manufacturer to make sure the proposed changes will not compromise performance or safety.

I have never tried the electrical lube you used so I don't know how well these types of products work. I am aware that there are many specialized deoxidizing solutions on the market that clean, preserve, lubricate, and improve conductivity on all metal connectors and contacts. I assume they work to some degree or they wouldn't be on the market.

One last possibility worth checking out is that the light bulb does not seat all the way into the socket. If this is the case, then the end of the light bulb could be just barely touching the metal tab centered in the bottom of the socket, which would also cause poor conductivity. With the power off to the post, remove the light bulbs and check each metal tab to make sure they are slightly raised. If necessary, you can lift each tab a bit using a small flat-headed screwdriver.

Good luck on finding a method that works for you, and keep me posted on the results!

UPDATE 4/16/06

I'm delighted to say this project did have a happy ending:

You hit the nail on the head with light bulb not making a good contact with the sockets. I have had the same bulbs in since the end of December. Good job, and thank you for the help. —Rod S.

Copyright © 2006 & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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