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beetlebz 12-06-2009 07:57 PM

Question about mixing bulbs with ballasts
Quick question about my 110g setup... The tank came with a home-made hood (nice one, too!) with a VHO ballast and 2 T-12 sized lamp hangers. I currently have it set up with 2 regular T-12s... but the problem is T-12's are impossible to find locally. So when one burns out, I'm stuck with shop light bulbs until I can order new bulbs online, and frankly its a royal pain to deal with the algae growth under "shop" lighting.

Provided I kept within the wattage limit of the ballast (which being a VHO ballast should be 110 watts x 2) would there be any harm in swapping to T-8 or even T-5 end caps to use those bulbs?

Byron 12-07-2009 02:41 PM

I believe T8 and T12 should be interchangeable. T8 is a slightly smaller (in diameter) tube that produces slightly more intense light for the same wattage so it should work. I can use either in my regular fixtures.

T5 requires different ends I think, so probably wouldn't fit. To date I have not found info anywhere saying T5 will work except in a T5 fixture.


JouteiMike 12-07-2009 02:55 PM

I recommend that you do not swap the T12s with T8s or T5s. Using T8 bulbs on a T12 ballast will decrease the lifespan of the bulb.

WisFish 12-07-2009 05:39 PM

I know the t-5 and t-8's are not compatible. The ballasts and wiring are different. Found that out the hard way when someone at the church kept putting the t-5 bulbs in the t-12 fixtures and couldn't figure out why the bulbs didn't last.

I agree with Byron that some all-glass fixtures claim to accept t-8 and/or t-12 bulbs. I don't believe you'd want one of each in the same fixture at the same time however.

jmlampert23 12-07-2009 07:54 PM

the t-8 t-10 and t-12 are all interchangable, t-5 needs a special fixture

beetlebz 12-08-2009 07:04 PM

so i can stuff a T-8 bulb in the T-12 socket without modification? the draw back being bulb life, do i understand this correctly?

Byron 12-08-2009 08:00 PM


Originally Posted by beetlebz (Post 287003)
so i can stuff a T-8 bulb in the T-12 socket without modification? the draw back being bulb life, do i understand this correctly?

Well, I can only say that I have used both T8 and T12 tubes in my fixtures, even one of each in the same one, and they have never exploded or overheated or... whatever. I replace the tubes every 12 months regardless due to the decreasing intensity of the light (they still light but it is not as bright) and I've never noticed anything with either type. I have read that T8 tubes will output more intensity longer, and some suggest they do not need replacing as often; I've no data to support or disprove this, something I need to research further.

But as WisFish stated, it is the T5's that cannot be used in regular fixtures.


JouteiMike 12-10-2009 01:48 PM

Going back to my post, it really depends on what the ballast is rated for. The ballasts are designed to run specific types of bulbs, this should be clearly printed on the ballast itself. If it is a T8 ballast, then only T8 bulbs should be run on it, if it is a T12 ballast, then only T12 bulbs should be run on it. I know the T12, T10, and T8 all have similar pins seem to be interchangable, but it really depends on the ballast. Since T8 bulbs run at a lower current than T12, they should really be run with a different ballast.
From my experience, running T12 bulbs in a T8 ballast would decrease the life the ballast because the T12 lamps run at a higher current. On the other hand, T8 Bulbs running on a T12 ballast would decrease the life of the bulbs because the current running through the bulbs would be higher than needed, overworking the bulb. This is just my two cents, if other people claim that they see no ill effects, then you should be fine. Just keep in mind there are no advantages to running certain types of bulbs in different types of ballasts, no added brightness or life of the bulb.

beetlebz 12-12-2009 08:03 AM

Thanks guys, thats exactly what I was looking for :) I think with what I have found and what you guys have said im going to get a couple T-8s to try, and note the intensity and bulb life. Like I said the ballast is rated for 2 VHO bulbs which means the ballast is capable of holding out for 220 watts minimum, where two 4' T-8 bulbs will only be drawing 64 watts so I do not at all fear for the ballast.

IF the bulbs last as long as the T-12s have, and IF the ballast suffers no ill effects (overheating, namely) I might even try wiring in two more sockets. But time will tell. thanks for all the input guys!

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