# T8 bulbs in a T12 fixture or vice versa.



## aftershockews (Dec 22, 2012)

What eventually damages what?


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## karl_r (Nov 5, 2012)

aftershockews said:


> What eventually damages what?


with the right ballast shouldn't be a problem


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## aftershockews (Dec 22, 2012)

karl_r said:


> with the right ballast shouldn't be a problem


Well that pretty much answered nothing. :thumbsup:


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## Lighting Retro (Aug 1, 2009)

T8 lamps on a T12 ballast, or T12 lamps on a T8 ballast will both fail prematurely. 

The only difference in the fixture itself is typically the ballast and the sockets. T12 will typically have unshunted sockets, and most T8 will have shunted sockets. 

Putting the wrong ballast in will either underdrive or overdrive the lamps causing the failures. Hope that answers your question.


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## aftershockews (Dec 22, 2012)

Lighting Retro said:


> T8 lamps on a T12 ballast, or T12 lamps on a T8 ballast will both fail prematurely.


That is what I have always told the customers without knowing why.
Thanks.


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## Lighting Retro (Aug 1, 2009)

10-4


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## Electric_Light (Apr 6, 2010)

Using T12 lamps on a T8 ballast would be just like an LED retrofit. 

You will reduce energy use, because the wattage goes down, but you lose output as well, again, just like most LED retrofit. The T12 4' lamp will look approximately like a 3 foot 25W lamp or a 4 foot 25W energy saver lamp.


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## bobelectric (Feb 24, 2007)

As a mistake I used t-8 in a t-12 light unit. after I left they flikered to beat all.


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## Electric_Light (Apr 6, 2010)

bobelectric said:


> As a mistake I used t-8 in a t-12 light unit. after I left they flikered to beat all.


Most T12 ballasts are magnetic rapid start. They're single application products. 

Most T8 ballasts from the last 5 years or so can take anything from 120 to 277v input and rated for 2-4' lamps and T12 lamps will appear like a 3' lamp to the ballast. It's hard to fry one aside from lifting a neutral on 277v and zapping it 480v. There's no harm in waiting out until the lamps burn out or area wide replacement if a few T12s get installed accidentally. No harm to the ballast/fixture, but don't gripe if the T12 lamps burn out in 6 months. 

You'll have issues with starting, flickering or poor output regardless of ballast/lamp combo if you use reduced wattage lamps if its cold enough to be uncomfortable for people, only use full wattage lamps. They're not rated for use under 60*F.


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## chicken steve (Mar 22, 2011)

Point taken EL.....

I've often wondered, but haven't asked

how does a _universal_ ballast work? :001_huh:



~CS~


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## Electric_Light (Apr 6, 2010)

chicken steve said:


> Point taken EL.....
> 
> I've often wondered, but haven't asked
> 
> ...


It's a (nearly) constant current power supply and various T8 lamps are rated for the same amps. The ballast can accommodate a wide range of voltage while still delivering the same current. The input side works like global worldwide voltage range phone chargers.


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## pete87 (Oct 22, 2012)

aftershockews said:


> What eventually damages what?




Here is an older thread on this 


.http://www.electriciantalk.com/f30/t8-bulbs-t12-fixture-29804/

check out post 11 



Pete


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## Electric_Light (Apr 6, 2010)

aftershockews said:


> What eventually damages what?


Light Emitting Decorations.. damages wallet.


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## Going_Commando (Oct 1, 2011)

Lighting Retro said:


> T8 lamps on a T12 ballast, or T12 lamps on a T8 ballast will both fail prematurely.
> 
> The only difference in the fixture itself is typically the ballast and the sockets. T12 will typically have unshunted sockets, and most T8 will have shunted sockets.
> 
> Putting the wrong ballast in will either underdrive or overdrive the lamps causing the failures. Hope that answers your question.


Speaking about shunted sockets and whatnot, I always loved the feature of T12 single pin sockets where removing the lamp disconnects power to the socket. I wish it was like that again instead of using those silly ballast disconnects or just cowboying it when replacing a ballast.


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## Texas_LED_Guru (Mar 1, 2013)

aftershockews said:


> What eventually damages what?


Nothing if you have the correct ballast.

A T12 ballast on a T8 bulb will over drive the T8 causing it to fail early on.

A T8 ballast on a T12 won't give you adequate light (if it lights at all) because its being under driven.

A T8 slides right into a standard T12 socket like butter. I just did a couple myself.

On the yellow wires sometimes you need to tie them all together with the single red on the T8 ballast unless it has the yellow wires on it.

That is the only issue I encountered.


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