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Thread: New T8 fixtures, will T12 bulbs work in them

  1. #1
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    New T8 fixtures, will T12 bulbs work in them

    I have part of a case of T12 bulbs I'd like to use up. They fit my new T8 fixtures and light up fine. Are they going to damage the new fixtures or ballasts?
    Thanks

  2. #2
    Quote Originally Posted by Andrew Joiner View Post
    I have part of a case of T12 bulbs I'd like to use up. They fit my new T8 fixtures and light up fine. Are they going to damage the new fixtures or ballasts?
    Thanks
    No! You will damage the ballasts or have very short lamp life, T8 lamps w/ T12 ballasts will burn out prematurely, I have not seen what you are asking but have seen the reverse. Ballasts are designed to be used w/ specific lamps & one should not use other then the lamps they were designed for.Compared to the old ballasts, the electronic ballasts have a short enough life as-is, no sense in reducing the life more.(They do not last as long as the older ones they replaced, it was not unheard of to find 30-40 YO ballasts still in service these are on borrowed time after 5 years).

  3. #3
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    Further, and I'd have to go look to confirm, I believe the pin size and spacing is different. T8 bulbs are also smaller in diameter.
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  4. #4
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    Jim,
    I wrote about the spacing difference here on SMC and was informed that the spacing is the same. I didn't measure the spacing myself but took the posters word for it. I did not check the pin size though.
    I made the mistake of installing T12s in my pole barn because the local electric supply had a sale on the T12s, should have done the research prior to buying. I now have flickering lights and buzzing noises that I wish I didn't have.
    David B

  5. #5
    All lamps are measured in 1/8" increments so a T5 is 5/8" T8 is 1" & so on..
    T8 & T12 lamps both use medium bi-pin bases they physically fit, & it's a common practice to retrofit from T12 to T8 & same lampholders are left in place.

  6. #6
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    The T12 bulbs fit my new T8 fixtures and light up fine. I was just concerned about ballast and bulb life.

  7. #7
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    I could see both bulb and ballast having reduced lif by mixing them. The T12s should be 40 watt, the T8s are 32 watts. The T12s probably aren't as bright as they should be, and it may be putting undue stress on the ballast. Sell the T12 bulbs to someone who can still use them. Jim.
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  8. #8
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    Thanks guys,

    I went and got some T8 bulbs @ Walmart, $6.47 for 2. I'll use up the T12 bulbs in other older fixtures.
    Last edited by Andrew Joiner; 05-10-2009 at 12:00 AM.

  9. #9
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    T 12s for T 8s

    There are few differences between T8 and T12 fluorescent bulbs. T8 bulbs are smaller in diameter than T12 bulbs (1 inch or 8/8ths vs. 1.5 inch or 12/8ths) and are available in the same lengths. Both use the same combination of gases to produce light. Both are available with a medium bipin configuration on the pins.

    The magnetic ballasts used in T12 fixtures are less efficient than the electronic ballasts used in the newer T8 fixtures. This results in a moderate reduction in energy consumption when the T12 ballasts installed in existing fixtures are replaced by T8 ballasts. The electronic ballasts used in the T8 fixtures also allow the bulb to be dimmed, which is not possible with other types of fluorescent ballasts. Before swapping tubes, be sure which type of ballast you have and verify that you're not swapping apples for oranges.
    Good luck,
    Jim
    Jim

  10. #10
    Quote Originally Posted by James A. Wolfe View Post
    There are few differences between T8 and T12 fluorescent bulbs. T8 bulbs are smaller in diameter than T12 bulbs (1 inch or 8/8ths vs. 1.5 inch or 12/8ths) and are available in the same lengths. Both use the same combination of gases to produce light. Both are available with a medium bipin configuration on the pins.

    The magnetic ballasts used in T12 fixtures are less efficient than the electronic ballasts used in the newer T8 fixtures. This results in a moderate reduction in energy consumption when the T12 ballasts installed in existing fixtures are replaced by T8 ballasts. The electronic ballasts used in the T8 fixtures also allow the bulb to be dimmed, which is not possible with other types of fluorescent ballasts. Before swapping tubes, be sure which type of ballast you have and verify that you're not swapping apples for oranges.
    Good luck,
    Jim
    In all cases dimming ballasts are required for dimming FL lamps, T8 or T12.

  11. #11
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    The lamp sockets are the same for T-8 and T-12, I have rewired old T-12 fixtures for T-8 lamps. The T-12 lamps draw more current than the T-8 so I would expect the electronic ballast to burn up on T-12 lamps.

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