Question for the lighting gurus! T8 vs T12?

[Dwarfnut]

Ok, so a while back, I bought a fixture to put over my 40 gallon breeder tank which is 36" x 18". The only 36" fixture I could find was at Lowes and it was a two light (what I wanted!) but used T8 sized bulbs accurding to the box. The problem is that I could only find T8 36" bulbs locally that were of the "shop light" variety and were only 4,100K. Using a pair of those quickly turned into a large outbreak of the blue-green slime algae I am still battling. I have removed those lights and replaced with some smaller CF lights for now.

So I went to the LFS and had them order a 36" buld in the T8 size with rating of 5,500 K. I went to get the light yesterday and realized it was only a 25 W bulb... all other 36" bulbs I've seen are 30W. SO I get it home and decide to check the fixture to see if maybe it lists 25 W as an option. I take the fixture apart and started reading the ballast and it says it's correct for 2 30Wt12 or 2 25WT12 bulbs. T12??!! WTH? So now I'm really confused... I thought you could not use T8 and T12 bulbs interchangably?? Can You?? I did try the new bulb and really like the color, but If I can just use T12 bulbs, then I could find them much easier and cheaper!

Thanks,
Bill C.

 

[Cichlid Woman]

As far as I know, it's only the length and the wattage you have to match to the fixture in fluorescent lighting. The T numbers can be variable. At least, that's how I do it with my own 20-watt fixtures. As far as I know, I can select any 24" 20-watt bulb I want to put in there.

Re-check with the Lowes guy, though--I don't want your system to short out because I was wrong ...

-- Pat

 

[goldfish freak]

I am no expert but I know that some fixtures can take either T8, T10, or T12, such as the 48 inch single or double strip light made by All Glass. If the ballast says that you can use T12's then by all means go ahead and do so. The manufacters of the ballast know what it can and can't handle.

 

[125gJoe]

Originally posted by Dwarfnut
Ok, so I thought you could not use T8 and T12 bulbs interchangably?? Can You?? .............
Thanks,
Bill C.

They are not interchangeable.

 

[Raithan Ellis]

Actually, many electronic ballasts that are manufactured for T-12 bulbs will run a T-8 bulb just fine... and another important thing to note, even though a T-8 uses less wattage than it's T-12 counterpart, the T-8 will put out more light due to it's more efficient smaller tube design. However, T-8's have a smaller selection of bulbs to choose from.

Cheers,
Raithan O. Ellis

 

[Dale W.]

You can generally run a t-8 in a t-12 socket with no problems. The t-8's are manufactured for electronic ballasts with a 25 watt output for t-8's and they run a bit coolerthan the old tar filled ballasts. The t-12 ballast is usually the old style tar filled coil type ballast. The lumens output of the t-8 is the same if not more than the t-12 bulbs with less wattage used.

In a nutshell, you can run t-8's on a t-12 ballast but you can not run t-12's on a t-8 ballast.

 

[Gumby7]

Originally posted by Raithan Ellis
Actually, many electronic ballasts that are manufactured for T-12 bulbs will run a T-8 bulb just fine... and another important thing to note, even though a T-8 uses less wattage than it's T-12 counterpart, the T-8 will put out more light due to it's more efficient smaller tube design. However, T-8's have a smaller selection of bulbs to choose from.

Cheers,
Raithan O. Ellis

Exactly. It comes down to the ballast type. Virtually all "consumer grade" T12 and most T8 fixtures you buy at your hardware store are magnetic. To get even better performance out of T8's you really need to step up to an electronic ballast.

Also, there are different "start" types. The oldest is "preheat" and can be recognized by the use of a starter. Next came "rapid start" (RS), followed by "instant start" (IS). I am not 100% sure on the difference in the last two but suffice to say virtually all (all?) T8's are IS. I believe IS is more energy efficient because the bulb cathode is only heated (or jolted with a high current) for a very short time (i.e. instanteous). However the power applied during this heating is substantial and this is why RS bulbs are short lived on IS ballasts. So there may be some backward compatibility and it may be possible to mix them up but you should really match your tubes to your ballast. If you read the ballast manufacturer’s literature they are quite specific that you select your bulb AND ballast as a combination.

Gumby

 

[Dwarfnut]

Thanks for the info guys... looks like I'll just stick to the T8's as they seem to fit a little better. The ballast does not say if it is an electric or magnetic, but I'd guess to say electric. The fixture is not very old... only about 6 months...

Bill C.