# Can i use T5 with a T8 ballast?



## GlassCat594

the plugs are different for a T8 (1" tube) than a T5 (5/8" tube). 

You would have to buy a converter. Sorry I can't provide more info on the converter


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## tyler79durdan

If the ballast is retrofitted with t5 endcaps and you use NO bulbs, you will have no problems.


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## f1ea

Yes, the sockets are different (and I think the length as well). But changing the sockets is easier than getting a new ballast AND sockets just for the T5s.

So basicaly, if I can work out the sockets/endcaps it should be no problem, from an electrical/functional point of view (ie under-driving, over heating, blinking, shorter bulb life etc). That's what i wanted to know.

Thanks!


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## TheRac25

yeah! i run a 4x32W T8 ballast into 2xT5ho bulbs, less bulb life due to instant starting instead of programmed start on a good t5 ballast only problem i can think of, but only turn on once a day so effect is minimal.


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## OverStocked

NO matter what,t he ballast determines the bulbs output, not the bulbs. SO you could put 30324234 watt bulbs in there, but they are going to be driven at 40 watts.

It will do nothing to help your current situation. At all.


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## [email protected]

If you can get adapters shipped from Europe, the switch would be easy. 
I didn't say cheap and easy. ;-)
If you don't mind some metal work and wiring changes, you can install T5 sockets and use T5 bulbs or lamps, but you will be getting the equivalent of over driven T5NO, not T5HO output. 
There are quite a few different ballast types so instant start, rapid start, and programed start may cause some issues, but it will work. 

Another option that might be easier, is to install an additional ballast, do a bit of rewiring, and over drive the existing T8 lamps.


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## f1ea

over_stocked said:


> NO matter what,t he ballast determines the bulbs output, not the bulbs. SO you could put 30324234 watt bulbs in there, but they are going to be driven at 40 watts.
> 
> It will do nothing to help your current situation. At all.


T5 bulbs have better penetration for the same wattage than T8. So a T5 bulb even at the same output has better pentration.

I will be using NO T5 - 28W bulbs, so they will be driven by the 40W ballast which will probably be working a bit less eficiently; but the real consumption is close to the 28W dictated by the bulb. The ballast does not create a consumption that the bulb is not demanding.



> If you can get adapters shipped from Europe, the switch would be easy.
> I didn't say cheap and easy. ;-)
> If you don't mind some metal work and wiring changes, you can install T5 sockets and use T5 bulbs or lamps, but you will be getting the equivalent of over driven T5NO, not T5HO output.
> There are quite a few different ballast types so instant start, rapid start, and programed start may cause some issues, but it will work.
> 
> Another option that might be easier, is to install an additional ballast, do a bit of rewiring, and over drive the existing T8 lamps.


Well, I can buy sockets for less than US$1.50 a pair. I would still need extra wiring and T5 if I get an extra ballast. Keeping the ballast and using NO 28W bulbs should be ok. All I have to do is remove the old sockets and place the T5 sockets... not much rewiring.


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## gpodio

> I will be using NO T5 - 28W bulbs, so they will be driven by the 40W ballast which will probably be working a bit less eficiently; but the real consumption is close to the 28W dictated by the bulb. The ballast does not create a consumption that the bulb is not demanding.


This isn't quite the case... they are called "ballasts" because they limit the current to the bulb. Fluorescent bulbs, once lit, offer little resistance to current, this is why one can overdrive them using a higher wattage ballast, they'll take as much as the ballast allows them to do so... until they break obviously. Same deal with MH lighting, resistance drops as the bulb heats up...

There are differences between T8 and T5 ballasts but not enough for either bulb to not work on either ballast.

Hope that helps
Giancarlo Podio


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## f1ea

gpodio said:


> This isn't quite the case... they are called "ballasts" because they limit the current to the bulb. Fluorescent bulbs, once lit, offer little resistance to current, this is why one can overdrive them using a higher wattage ballast, they'll take as much as the ballast allows them to do so... until they break obviously. Same deal with MH lighting, resistance drops as the bulb heats up...
> 
> There are differences between T8 and T5 ballasts but not enough for either bulb to not work on either ballast.
> 
> Hope that helps
> Giancarlo Podio


Thanks!
I didnt know the fluorescents had little resistance.

However, when most people overdrive the NO... they are plugging 2 positives. There is much overdrive with just a little extra capacity in the ballast. That was my original question though... how much is it possible to use the T5 with a T8 ballast. It seems it is not that complicated and that it works.

I went to shop to buy the T5 28W bulbs, but they were out, they'll have them by friday. They did have the sockets.

Lets say the 40W ballast will overdrive the 29W T5 bulb... its not a big problem (considering its overdriving my 32W T8s as well) and I will not be overdriving them with 2x positives....


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## gpodio

Using two 20W positives from an electronic ballast is no different than using a single positive from a 40W ballast... it's just like putting two batteries in parallel, you're just combining/adding the current the bulb can draw, voltage and frequency remains the same.

Ignoring some differences in efficiency as good T5 ballasts usually operate at higher frequencies than T8 ballasts do, the 28W T5 tube on a 40W ballast should perform somewhere in between a standard 28W T5 and a 54W T5HO. In the future you can always upgrade the ballast to a 54W T5HO model and squeeze a little more light from your setup. If you find the T5NO bulbs don't last very long (unlikely), use T5HO bulbs instead as they have better filament coatings to better handle the extra current.

I have a 4x32W T8 ballast driving two 32W T6 bulbs, they last me a little over two years running at 64W each. The ballast is a standard 20KHz ballast, when it dies I'll be replacing it with a 40KHz T5HO ballast which should give me better lumen maintenance over the life of the bulb on top of a little better efficiency.

PS. It's also possible your 40W ballast is actually a T12 ballast rather than a T8. However most modern T12 ballasts operate at higher frequencies than the older models used to, making it just as good of a choice.

Hope that helps
Giancarlo


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## Wasserpest

Hi Giancarlo, welcome to the Planted Tank! :bounce:

OP - There are many different kinds of ballasts, and they all behave a bit differently when connected different bulbs. Can you open up your fixture and tell us the Brand/Model of your ballast?

Keep in mind that you could use T5HO bulbs as well... they behave very similar to T5NO bulbs when connected to the same ballast. Even though their "rating" is 28 vs 54W, they will light up with the same wattage @ the same ballast.

I have several 4x32W (Advance, Sylvania) ballasts driving T5 bulbs, and connecting 2 leads (ODx2) runs one bulb at ~45W, and two at ~40W each, while connecting one lead to four bulbs runs them at ~30W.

But again, just an example, different ballasts will give you different results.


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## gpodio

Correct, not all ballasts are suitable for overdriving and/or combining feed circuits. Some of the more flexible ballasts measure the impedance of the bulb to determine the length and therefore the wattage required, such a ballast cannot be used for overdriving, it can however be used to drive different diameter bulbs but they tend to have conservative ballast factors.

I'm using the Sylvania QuickTronic QT4X32/120 LP ballasts for overdriving purposes. Also using Fulham and IceCap ballasts to run VHOs and Overdriving PCs but for the price, the QuickTronics are very flexible and the wiring is as simle as can be: 4 feed circuits and two returns. Internally it has two 2x32W circuits and the neutrals are bridged together so little chance of getting the wiring wrong. Also using QT2X32/120 ballasts for driving 55/65W PCs...

This is one of the older fixtures I have put the QT4X32 into, this particular ballast lasted 6 years before failing: (Telling me I can't post links...) go to gpodio dot com and click articles, then the article on overdriving...

PS. Thank you for the welcome! It's been so long I couldn't figure out what my old login was 

Regards
Giancarlo


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## f1ea

Wasserpest said:


> OP - There are many different kinds of ballasts, and they all behave a bit differently when connected different bulbs. Can you open up your fixture and tell us the Brand/Model of your ballast?
> 
> *Keep in mind that you could use T5HO bulbs as well... they behave very similar to T5NO bulbs when connected to the same ballast. Even though their "rating" is 28 vs 54W, they will light up with the same wattage @ the same ballast.*


Thanks!
They did have the 54W HO bulbs at the store (were out of NO)... this was the next question! that's what I am going to do: HO bulb it is.

Will open the panel and check on the ballast. I think it is General Electric, but I dont remember.



> Ignoring some differences in efficiency as good T5 ballasts usually operate at higher frequencies than T8 ballasts do, *the 28W T5 tube on a 40W ballast should perform somewhere in between a standard 28W T5 and a 54W T5HO. In the future you can always upgrade the ballast to a 54W T5HO model and squeeze a little more light from your setup.* If you find the T5NO bulbs don't last very long (unlikely), use T5HO bulbs instead as they have better filament coatings to better handle the extra current.
> 
> Hope that helps
> Giancarlo


I figured, the NO would be a bit overdriven... but yes, the best is to get the HO and 'underdrive' it.

I dont really want to drive the lighting too high (ie go full HO); my aim is to improve penetration and increase a bit of intensity and focus at where the foreground/carpet is. The other plants are growing fast enough (tank gets some sunlight).

Thanks both, Great info! 

Giancarlo... pretty knowledgeable for a newbie eh 
(these fluorescent bulbs/ballast thing just reset everything I knew about resistance and electricity hehe)


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## gpodio

f1ea said:


> Giancarlo... pretty knowledgeable for a newbie eh
> (these fluorescent bulbs/ballast thing just reset everything I knew about resistance and electricity hehe)


lol

Your knowledge is fine, it's just discharge based lighting that doesn't follow the norm. Wikipedia has a good paragraph on the electrical aspects of fluorescent bulbs that talks about negative differential resistance. I'd link to it if I had a couple more posts under my belt.

Regards
Giancarlo Podio


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## Wasserpest

G - I think 5 posts is the threshold, so you should be able to link away freely now. I was trying to find your old username, but couldn't come up with anything. Maybe it was a different forum.


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## gpodio

Thanks, I found it, last post was from 2004  I'll keep this one!

Here's the links:
One of my ODNO fixtures
Fluorescent Wiki

Giancarlo


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