T4 Compact Fluorescent Question

[Kirk]

We have ceiling fixtures at work that are supposed to take two 7-watt or 9-watt fluorescent bulbs. We've been replacing the burned out bulbs with 5-watters to save energy. The 5-watt bulbs are supposed to last 10,000 hours. They've been lasting maybe 2500 hours (10 hours a day for 8 months). Are they blowing because they are being over-driven or are fluorescents different and as long as they fit in a fixture you are good to go? Any info would be greatly appreciated.
Regards,
Kirk

[Chris M.]

It`s more than likely they are burning out from being overdriven. And I doubt the fixture is taking less power in that configuration either, not significantly at least. Some fluorescent tube ballasts (usually built in to the fixture) are designed to drive a wide (ish) range of wattages, but others are very strict on what tube they must be used with. I`d go back to the required 7-watt tubes - not only should they then last the specified lifetime but also the ballast stands less chance of being damaged or havintg *its* life reduced too.


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[Kirk]

Chris M.,
Thanks for the info. I guess I'll start buying the 7-watt bulbs and replace the 5-watters as they go bad.
Regards,
Kirk

[Brock]

As Chris said most likely they will actually take the same wattage running 7w or 9w in there. They did that all over campus here and after about 18 months replaced all the ballasts.