Fluorescent bulb acting up

Discussion in 'Lighting and Electrics' started by Christian Lake, Sep 9, 2019.

  1. Christian Lake

    Christian Lake Member

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    so the other day I was going through Qs for our show, and noticed this fluorescent light acting weird, sometimes it works but sometimes it doesn’t. Now we did work on this last year because it wasn’t working, so we replaced the ballast and the light last year which in my opinion I don’t think it could have gone out that fast. Could it possibly be a short? Ever since our school had a renovation in 2009 this light fixture has been giving us problems. Any clue on what it could possibly be?
     
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  2. RickR

    RickR Well-Known Member

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    My first guess is that the new ballast isn't exactly like the others. There are several ways to it could be 'just wrong' but it only takes one!
     
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  3. Christian Lake

    Christian Lake Member

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    Yeah but what’s weird about it is that if it comes on first before the rest do then it doesn’t turn on but if it comes on exactly when the others come on it works. We’ve replaced this ballast about 10 times already. Everything in that fixture is brand new
     
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  4. RonHebbard

    RonHebbard Well-Known Member Premium Member

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  5. microstar

    microstar Well-Known Member

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    It's obvious that these are on a dimmer, so they need to have "dimmable ballasts". Chances are the one that is misbehaving either doesn't have a dimmable ballast or if it does, it is not an exact match to all the others that do work properly. Or I could be totally wrong.
     
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  6. Christian Lake

    Christian Lake Member

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    @RonHebbard it is on a Lehigh dx2 dimmer rack some of these fluorescents are also on an emergency modules in case the power goes out
     
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  7. RonHebbard

    RonHebbard Well-Known Member Premium Member

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  8. Mac Hosehead

    Mac Hosehead Well-Known Member

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    Since the fixture is running from a dimmer rack, I might assume that it has a 2-wire dimmable ballast. Ballasts of this type can vary as to how well they perform when dimmed. I would also have to assume that the current ballast in the fixture was not replaced with the same ballast as the original. ETC used to have a sheet that showed which ballasts worked better with their systems but I cannot find it. One ballast I believe I can recall working well was this:
    https://www.iballast.com/media/pdf/advance/Mark-10-powerline-brochure-v1.pdf

    Other issues can affect dimming performance such as good grounding. ETC also recommended running new lamps at full for 100 hours before normal use.
     
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  9. JD

    JD Well-Known Member

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    Dimmable Florescents are a tricky business. Unless all your ballasts are of the same type, hopefully from the same run, and your lamps are age matched from the same batch, then getting a real good match will be a problem.
    There are variances in tube gassing that may change the point where they strike-on. In addition, even ballasts of the same part number may vary in construction year-to-year.
    There are usually two circuits feeding the ballast, one is on all the time and preheats the cathodes as soon as it sees voltage on the second circuit, which is the one from the dimmer. The actual design of the circuit varies depending on the manufacturer.
    Putting a small (100 watt) ghost load on the circuit that is dimmed may prevent misfires.
     
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  10. Christian Lake

    Christian Lake Member

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    Could it possibly have something to do with how all of the fluorescents don’t turn off at the same exact time?
     
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  11. abbyt

    abbyt Active Member

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  12. Les

    Les Well-Known Member

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    That's a symptom of the same problem. Once you start relamping, replacing ballasts, etc; it seems like no two fluorescent fixtures will ever dim the same way again. Read JD's post again.

    I know why some schools have fluorescent houselights (cost, efficiency, labor) but it still makes me cringe. They never look good, even when operating correctly.
     
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