T12/T8 interchangable

james0816 · 01-19-2013, 03:33 PM

I hate when lights fail!!

So I have an older T12 fixture to replace it but only T8 bulbs. I seem to recall (or so I thought) that the T12 and T8 bulbs can be used in the same balast correct?

Darkblade48 · 01-19-2013, 08:17 PM

Depends on the ballast.

RickRS · 01-20-2013, 12:29 AM

Likely not, if it has a "magnetic" ballast typical of a old T12 fixture. I believe the strike voltage (point where gas ionizes and electric arc within the tube start the glow) for a T8 is higher than that of a T12. Magnetic ballasts for T12 won't reach the voltage level needed for a T8.

You can try it. If the ballast is insufficient it will either not light or flicker badly.

Depending on the length, you can still find T12 tubes of 5,000K to 6,700K in home improvement stores' lighting sections.

**Hoppy** · 01-20-2013, 02:04 AM

The original T8 bulbs were substituted directly for T12 bulbs, for power savings. I used to use a DIY light with T8 bulbs and a magnetic ballast, and it worked fine, except when the temperature dropped below about 65F, as I recall, then the bulbs wouldn't light. At normal 70F+ room temperature, it worked fine, discounting the flicker and hum.

james0816 · 01-30-2013, 11:59 AM

Just a quick update...since I still haven't got a new light yet.

The bulb does flicker for a couple of minutes after I first turn it on and then it stays lit. I'm guessing it just has to come up to temp is the reasoning behind that?

But...it's working so far so I'm good with that until I can replace it all together.

01-19-2013, 03:33 PM	#1
james0816 Planted Tank Guru (View User Tanks) PTrader: (60/100%) Join Date: Jun 2008 Location: VA Posts: 2,016	T12/T8 interchangable I hate when lights fail!! So I have an older T12 fixture to replace it but only T8 bulbs. I seem to recall (or so I thought) that the T12 and T8 bulbs can be used in the same balast correct?

01-19-2013, 08:17 PM	#2
Darkblade48 Moderator (View User Tanks) PTrader: (3/100%) Join Date: Jan 2008 Location: Toronto Posts: 7,049	Depends on the ballast. __________________ Anthony A Primer to Pressurized CO2 and A Primer to Planted Tanks Eheim Pimp #362 - Eheim 2213 x2, Eheim 2028, Ehein 2217, Eheim surface skimmer and Eheim autofeeder. Victor Pimp #33 - HPT272-125-350-4M

01-20-2013, 12:29 AM	#3
RickRS Planted Member (View User Tanks) PTrader: (0/0%) Join Date: Dec 2010 Location: NW Florida Posts: 221	Likely not, if it has a "magnetic" ballast typical of a old T12 fixture. I believe the strike voltage (point where gas ionizes and electric arc within the tube start the glow) for a T8 is higher than that of a T12. Magnetic ballasts for T12 won't reach the voltage level needed for a T8. You can try it. If the ballast is insufficient it will either not light or flicker badly. Depending on the length, you can still find T12 tubes of 5,000K to 6,700K in home improvement stores' lighting sections. __________________ Eheim Pimp #459 - 2213, 2234 SunSun Pimp #47 - (Perfect) HW302

01-20-2013, 02:04 AM	#4
Hoppy Planted Tank Guru (View User Tanks) PTrader: (52/100%) Join Date: Dec 2005 Location: Sacramento, CA Posts: 17,206	The original T8 bulbs were substituted directly for T12 bulbs, for power savings. I used to use a DIY light with T8 bulbs and a magnetic ballast, and it worked fine, except when the temperature dropped below about 65F, as I recall, then the bulbs wouldn't light. At normal 70F+ room temperature, it worked fine, discounting the flicker and hum. __________________ Hoppy

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01-30-2013, 11:59 AM	#5
james0816 Planted Tank Guru (View User Tanks) PTrader: (60/100%) Join Date: Jun 2008 Location: VA Posts: 2,016	Just a quick update...since I still haven't got a new light yet. The bulb does flicker for a couple of minutes after I first turn it on and then it stays lit. I'm guessing it just has to come up to temp is the reasoning behind that? But...it's working so far so I'm good with that until I can replace it all together.