T12/T8 interchangable - The Planted Tank Forum
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post #1 of 5 (permalink) Old 01-19-2013, 03:33 PM Thread Starter
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T12/T8 interchangable

I hate when lights fail!!

So I have an older T12 fixture to replace it but only T8 bulbs. I seem to recall (or so I thought) that the T12 and T8 bulbs can be used in the same balast correct?
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post #2 of 5 (permalink) Old 01-19-2013, 08:17 PM
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Depends on the ballast.


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post #3 of 5 (permalink) Old 01-20-2013, 12:29 AM
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Likely not, if it has a "magnetic" ballast typical of a old T12 fixture. I believe the strike voltage (point where gas ionizes and electric arc within the tube start the glow) for a T8 is higher than that of a T12. Magnetic ballasts for T12 won't reach the voltage level needed for a T8.

You can try it. If the ballast is insufficient it will either not light or flicker badly.

Depending on the length, you can still find T12 tubes of 5,000K to 6,700K in home improvement stores' lighting sections.

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post #4 of 5 (permalink) Old 01-20-2013, 02:04 AM
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The original T8 bulbs were substituted directly for T12 bulbs, for power savings. I used to use a DIY light with T8 bulbs and a magnetic ballast, and it worked fine, except when the temperature dropped below about 65F, as I recall, then the bulbs wouldn't light. At normal 70F+ room temperature, it worked fine, discounting the flicker and hum.

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post #5 of 5 (permalink) Old 01-30-2013, 11:59 AM Thread Starter
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Just a quick update...since I still haven't got a new light yet.

The bulb does flicker for a couple of minutes after I first turn it on and then it stays lit. I'm guessing it just has to come up to temp is the reasoning behind that?

But...it's working so far so I'm good with that until I can replace it all together.
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