# T8 Lamps installed on a T12 ballast



## 1joeyj (Nov 21, 2011)

What would happen if you installed T8 lamps onto a T12 ballast? They are 2 lamp 3' and 4' luminaires.


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## Podagrower (Mar 16, 2008)

I did it once a long time ago. We had a construction trailer with 4' lights missing bulbs. There was a case of t-8 bulbs in the back. Some turned into wicked awesome strobe lights, some didn't work, some were very dim, but kind of lit.

I recently replaced a t-12 ballast in a 8' fixture with a t-8 ballast. The fixture already had t-8 bulbs in it, it kind of worked.


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## 10492 (Jan 4, 2010)

Depends, you have to look at the ballast. Some will run T12, T10, and T8.


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## Chris1971 (Dec 27, 2010)

Probably reduced lamp life would be one symptom.


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## Cletis (Aug 20, 2010)

*End*

There would be a catastrophic explosion of biblical porportions


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## Electric_Light (Apr 6, 2010)

1joeyj said:


> What would happen if you installed T8 lamps onto a T12 ballast? They are 2 lamp 3' and 4' luminaires.


T12 is 0.43A (or thereabout) and T8 is 0.265A.
The operating voltage is much higher on T8. 

On magnetic T12, the lamps either won't start/flash obviously or if it manages to remain lit, either the ballast or lamp will fail soon. 

On electronic T12, the ballast will have enough voltage to strike a T8. The ballast will operate at higher wattage than intended, because the voltage is higher while providing the same current, its likely that ballast will fry.


on the other hand, running T12s on T8 ballast will cause them to operate as if a 25W 2' lamp was fitted in place. They will simply run at reduced power. On an instant start without cathode heater, the cathodes may not stay hot enough and ends may blacken rather early.


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## MarkyMark (Jan 31, 2009)

1joeyj said:


> What would happen if you installed T8 lamps onto a T12 ballast? They are 2 lamp 3' and 4' luminaires.


They will work for awhile and then fry the ballast. Judging from the gym where I replaced about 30 ballasts a couple of years ago, about 75% of them will burn out within three months. This, after an enterprising gym manager changed out every T-12 lamp in the place to T-8's to "save money."


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