Thanks for the very informative reply! The bulbs have lasted a couple of years already.
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We have a kitchen illuminated by 48-inch fluorescent lights above a
translucent suspended ceiling. We are slowly upgrading them to
electronic ballasts and F32T8 bulbs.
In the meantime, here's tonight's discovery:
F32T8 bulbs work fine in F40T12 fixtures. In fact, they even work in
fixtures that are finicky with F40T12 bulbs (presumably because the
ballasts are getting old).
Have others had the same experience? Am I shortening the bulb life, or
anything, by running an F32T8 bulb on a ballast designed for an F40T12?
I know that *theoretically* I may be putting more current through it...
in practice, does it make a difference?
If your existing fixture does indeed have an electgromagnetic ballast designed for the F40T12 lamp, then the following applies:
The major difference between an F40T12 fluorescent tube and an F32T8 tube is the current rating. The F40 is rated for 0.430 amps; the F32 is rated for 0.265 amps. Once a fluorescent lamp has started, the ballast acts
like a current source and drives the lamp according to the load current rating of the ballast.
In this case, it's a little surprising that the F32T8 lamp starts, but that can happen -- especially when the lamp is new. However, the lamp is being overdriven by about 60%. Fluorescent lamps can be overdriven by 10% or so without major problems, but you are likely overheating the cathodes and driving the lamp quickly toward end-of-life due to cathode deterioration.
Putting an F40T12 lamp on an F32T8 ballast is less destructive since the F40 will be under driven. It will be low in light output, but it will start and likely last for its rated life.
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