Hi -

I took FOUR 55W HO T8 Germicidal bulbs and plugged them into a fixture meant for FOUR 32W HO bulbs. They seem to power up just fine. I understand that using the wrong ballast may reduce the bulb life, but once the bulb is powered, does it run at full lumens? Is there any way to figure this out? I would prefer to keep the setup as-is rather than having to purchase and rewire a new ballast.

My application is different than the normal lights that are powered for several hrs per day. These lamps are turned on for a max of 20minutes at a time, and then allowed to cool. Does that make it any better in terms of ballast load?

Your professional insight would be greatly appreciated!

Do you mean a fixture for normal 32w T8 lamps? If so they will run at the ballast's output (approx 32w if its a full-power ballast).
May shorten lamp life, but won't hurt the ballast.

What you don't want to do is exceed the lamp length that the ballast was designed for, as it will attempt to drive drive based on length.
So you will overdrive the ballast (lamp may actually be running close to its correct power).

(note: I'm talking Electronic & HPF magnetic ballasts here)

Do you mean a fixture for normal 32w T8 lamps? If so they will run at the ballast's output (approx 32w if its a full-power ballast).
May shorten lamp life, but won't hurt the ballast.

Yes, the fixture is for 32W T8 lamps, but at 4'. I actually shortened the fixture to take the 3' T8 55W bulbs.

So the new bulbs will run at below full capacity, correct? Or with shortening the bulb help increase the output closer to 55W?

Yes, the fixture is for 32W T8 lamps, but at 4'. I actually shortened the fixture to take the 3' T8 55W bulbs.
So the new bulbs will run at below full capacity, correct? Or with shortening the bulb help increase the output closer to 55W?

Yep they will run below full capacity.
The ballast will "see" 3-feet of lamp.. so it'll run around 25w (standard power for a 3' T8 lamp).
If its an instant-start ballast you can do overdrive wiring - 2 outputs to each lamp (works with most instant start ballasts), that would give between 38w-43w per lamp. (you'd ofcourse need a 2nd 4-lamp ballast)

Yep they will run below full capacity.
The ballast will "see" 3-feet of lamp.. so it'll run around 25w (standard power for a 3' T8 lamp).
If its an instant-start ballast you can do overdrive wiring - 2 outputs to each lamp (works with most instant start ballasts), that would give between 38w-43w per lamp. (you'd ofcourse need a 2nd 4-lamp ballast)

Wow, very interesting info. I would definitely like to maximize output, could you elaborate a bit on adding the second ballast please. Would I need the exact same ballast, and what would the wiring look like? Each ballast powers 2 lamps? Or connect the second ballast in parallel to the first?

Thank you!

You probably have something that (electrically) looks like the 1st pic...wire colors vary between ballast brands, on some you might have 2 blues+2 reds where I show 4 blues, and 2 yellows where I show red. (could also have just one red)

Basically all you do is put 2 outputs into one lamp like the 2nd picture. Ballasts don't need to be the same model or brand.
As mentioned this works with most T8 instant-start ballasts (atleast that I've tried), but some won't (I know for example certain GE models that have EOL protection won't do it)


Note: if your ballast has 2 wires going to each end of the lamps, then its programmed-start or rapid-start .. this trick won't work!
You'll need to get T8-HO ballasts (not all that common, but they do show up on eBay). T5-HO ballasts will also work.

Excellent, looks like this will work for me. Thank you!
One more question: Should I go with Philips Advance or an off-brand on Amazon? Does it matter performance-wise? 

Thanks again!

Welcome!
 
I've used off-brands from eBay (just for general lighting), and found some are junk, others seem ok.

I know some members here have mentioned having issues with quality on Philips/Advance
My personal choice would probably be Osram/Sylvania or GE (depending what I was using it for, in your case probably skip GE since some have EOL protection & that won't work with 'overdrive' wiring). Oh and Fulham/Workhorse seem to be decent too.

Osram/Sylvania coming my way! I'll let you know how it turns out.

What would I need to do to run these lamps at full 55W power?

To run them at 55w you'd really need to find the actual ballast they were designed for.
55w is an oddball wattage - a normal 3' T8 HO would be 33w, and 3' T8 VHO would be 63w (neither actually exists, but based off the 4-foot versions of those 2 (44w & 84w respectively) that's what they'd run at)

You could probably get a T12/HO rapid start ballast for them. The F36T12/HO lamps run at 50 watts so it would be closer to the proper 55 watts.

Also, be sure to use a metalized reflector. white paint will absorb UV and halve your output.