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T-8's, T-10's, and T-12's; cheap shop lights

I've noticed that there seems to be some confusion about fluorescent tubes 
and appropriate ballasts, so I thought I'd add my 2 cents.  Before I begin, 
let me tell you that I don't intend to give specifics here since I am not 
very familiar with the wide range of tube types, diameters, and wattages 
available for aquarium use.  I am more familiar with what's available for 
commercial use so I just hope to try to clarify the terminology.  I'm also 
not including VHO's in my discussion since I know little about them.

First the tube diameter.  The 'T-' number refers to the diameter of the tube 
in eights of an inch, _regardless_ of its length or wattage.  So a T-8 is 
8/8ths, or one inch in diameter.

S. Wong said that , "I read in a posting that not all 1 inch diameter bulbs 
are really T8 bulbs, they might be T12's."  I think what the original poster 
meant was that although the particular T-8 tube being discussed was thinner 
than the T-12(same length), it used the same ballast.  From what I've seen 
in the pet stores, I believe this to be true.  So you can have an aquarium 
hood with the appropriate ballast to run a 40W 4' tube, regardless of its 
diameter (well, as long as the hood will physically accommodate the diameter 
of the tube.  One hood that I had could not hold anything wider than a T-8, 
to allow 2 tubes to take up the space normally used by a 1 tube fixture.) 
 It makes sense to me that aquarium-specific tubes would be designed to be 
used in standard aquarium fixtures, in terms of their ballast requirements.

In the commercial lighting world, 'T-8' is commonly used to refer to the 32W 
4' tubes being retrofit to older lighting fixtures in buildings.  These are 
usually driven by electronic ballasts that are specifically designed for 
them.  These ballasts should not be confused with the electronic ballasts 
designed for 40W 4' tubes.  If you simply ask for a ballast for a T-8 tube 
at an electrical supply place, this is what they may have in mind.

What about the cheap shop light fixtures, some of which come with electronic 
ballasts?  I only have third hand info to offer here, but here it is.  Some 
(most? all?) of these with el. ballasts are designed to drive the 
'energy-efficient' 34W 4' tubes.  Although the 34W tubes were originally 
designed to replace 40W tubes, using the same ballast, the electronic 
ballasts in some of the cheap shop lights don't appear to be able to last 
long when driving a 40W tube.

I hope I was clear on all of this.  If you have questions, I'll try to 
clarify them if someone else doesn't first.  If anyone has experience that 
contradicts, or clarifies, what I said, I'd be glad to hear about it.

I heartily second the recommendation to go to your local electrical supply 
house.  Bring the old tube, and even the fixture.  They should be able to 
help you find what you need.

Finally, some of you may be unaware that the manufacture of 'common' (e.g., 
Cool whites, not the fancy ones like Chroma 50's) 40W 4' tubes for the U.S. 
was stopped by the govt. in October '96.  So if you want them, buy them now. 
 The 34W energy efficient ones are still being manufactured.

Wade Shimoda (I'm an engineer but I don't work for any lighting manuf.)
Honolulu, HI