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  1. #11
    Join Date
    Jan 2011
    Columbiana, Alabama

    Default Re: flickering fluorescents

    Ice, as I stated earlier, flourescent lighting can be very complicated and is highly engineered. Yes, distance to the metal is critical so if you switch from a T12 (1 1/2" diameter tube) to a T8 (1" diameter tube) you may have exceeded the 1/2" limitation, unless you changed out the lamp bases (tombstones).

    And, the list goes on and on. Here is an excellent website to learn all you ever wanted to know (and more) about the topic. It's free and available to anyone, but you do need to register to take the course.
    Good Luck from Columbiana, Alabama
    Maurice Turgeon,

  2. #12
    Join Date
    May 2010

    Default Re: flickering fluorescents


    i'll check it out
    just had a thought (not that it matters)
    the difference between 1 1/2" diameter and 1"diameter is only 1/4" from center to outside

  3. #13
    Join Date
    Aug 2007
    The Great White North

    Default Re: flickering fluorescents

    Quote Originally Posted by iceman11 View Post
    yes, i realize now that there are compatibilty issues, and i was not aware that the distance from the shields could be a problem. i just don't want to switch ballasts, and then need to switch back to the original setup if they don't work properly due to that distance. cost is not an issue, as i can get the T8 32 watt ballasts for less than $10.00 each.

    Considering two of four fixtures seem to be working it may have nothing to do with the tubes being too far from the grounded shield. A simple test is to touch the glass portion of the tube and if your body's large capacitance causes them to light then it's a ground issue.

    i really like the better light output, and can really use it in my windowless 7'-0" x 17'-0" workshop. i also would rather not replace the entire fixture, because the previous owners drywalled around them alomost flush with the bottom of the fixture.

    T12 fixures have been successfully converted to T8 simply by the procedure mentioned earlier for that very reason.

    if you look at my original post again, you'll see that i replaced the bulbs in two other fixtures (in a different room), and they seem to be working fine. the distance factor doesn't seem to be a problem there. could they be working better because they have electronic T12 ballasts? (still incompatible?), or could they be T8 ballasts and still worked with the T12 bulbs? i don't know what ballsts are in there, but i will check it out and probably replace them.

    It's possible they are T12 electronic -- probably not though since there is a difference in cost between the magnetic and electronic T12 ballast.
    No one knows what type of T12 fixtures are there --- for all we know you could have pre-heat starters which are not needed with rapid-start tubes.

    FYI: i don't know how recently the T8 system came into play, but we have only been in this house for about 4 years.

    If I recall the T8 came into being sometime in the early '80's whereas the T12 have been around since the '30's.

    thanks for all the info. i learned something new (that's always good)
    Personally , for $10 seems to me a small price to shell out to resolve your dilema. Try one and find out.

    Besides, you'll eventually have to do it at some point since T12 are on the same road as incandescent lamps --- they are to be discontinued sometime within the next year or so.

    2 cents worth.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #14
    Join Date
    May 2010

    Default Re: flickering fluorescents

    update + question:

    the 2 fixtures in my shop indeed had T12RS magnetic ballasts, and i wiil change those. the other 2 fixtures (where the T8 bulbs are working fine) actually have T8 electronic ballasts. i don't know why there were T12 bulbs in these, but they did work fine.

    now the final question:
    in the fixtures where i am going to replace the ballasts, one end of the fixture has (2) blue wires on one "tombstone" and (2) red wires on the other one. the opposite end has (2) yellow wires on one "tombstone" (cneected to the ballast), an (2) white "jumpers" connecting that "tombstone to the other.
    as canuk expalined, i plan to connect the (2) blue wires together, the (2) red wires together, and the (2) yellow wires together, with each connected to the proper wires from the ballast. i don't have the ballast yet, so i don't have a wiring diagram.
    will the (2) white "jumpers pose any problem?
    will i need to change out the "tombstones also? if so, it may be only a few dollars more to replace the whole fixture. it may be easier too, but i didn't really pay attention to how they were mounted. the ceiling of my shop is the bottom of my concrete porch slab - drywall is probably furred out from there

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