Operating T8s on T12 Ballasts

[Mike]

Hey guys. Can 17W T8 lamps be operates on 14-15-20W magnetic trigger start ballasts without any side-effects? I know my orthopedic has four lamp F20T12/TS troffers at his office and i was thinking offering to either do a group balalst replacement to electronic 2X F32T8 ballasts (with two 17W T8s run in series on each side of the fixture) or simply bring up the fact that he can start using T8s in the existing fixtures to get more light.

[GEsoftwhite100watts]

No idea but you could try...
I did however recently find out from xmaslightguy that you can run F40T12s on F32T8 electronic IS ballasts...

[joe_347V]

2' lamps seem to be more compatible with each other than 4' lamps. Just make sure the T8s start reliably since they have a higher starting voltage and some trigger start ballasts can't start them. Preheat ballasts should do fine with 2' T8s. 

[Mike]

Yeah I've noticed newer chokes even list 2ft T8s on the ballast! (usually 18W ones, but is there really that much of a difference between 17 and 18W T8s? I know 18W ones are more of an appliance lamp...) I guess i'll mention it to him next time i go.

[GEsoftwhite100watts]

Well I guess the F40T12 or F34T12 on the F32T8 ballast works, in fact just today I had to do that with my bathroom light (a Lithiona 2XF32T8 wraparound light with (I THINK) an Advance electronic IS ballast...anyway one lamp died (a Sylvania Octron 3500K) which had been developing blackening for awhile but not as long as the GE EcoLux F32T8 next to it that has had blackening on both ends for almost a year and still worked fine).  Anyway I replaced those (group-relamped even though only the Sylvania was bad) with some post-EPACT, pre-2003 GE 34w Watt-Misers. They striate at first, but even after they warm up they seem dim and greenish and ugly and gloomy and dingy...maybe I'll get used to them eventually.  I've known these exact lamps to get dim and dingy as they age, even the glass/phosphor turns brownish! Even though they aren't halophospate (since they're post-EPACT) they still render wood kinda greenish, and as odd as it sounds it's like being under MV but still not quite like that...a camera wouldn't properly capture the effect I don't think...

[Mike]

Hmm. Well on a 32W ballast, the lamps are probably being underdriven, which is why you get that nasty color lol.

[A_lights]

Sometimes the 17W lamps start, sometimes they don't, usually trigger start ballasts even when grounded with new lamps (of Any type) just barely start up

I would recommend some triphosphorF20T12 lamps or with higher lumens for more light, and if you convert to T8 a 2 lamp ballast (IS or PRS) will be rated down to 2 foot lamps, I've even run F15T8 18IN lamps fine

[GEsoftwhite100watts]

Yeah, trigger start ballasts can be rather unreliable at times. 
Yeah, I bet those 34 watters in my bathroom light are somewhat underdriven...

[vaporeyes]

Trigger start ballasts IMHO barely start proper T12 tubes. You might get a 2' T8 to light if you switch to T8 low-profile sockets so the tube sits closer to the grounded reflector. Preheat or instant-start electronic ballasts are the way to go for 2' and under; with a rapid-start or trigger-start ballast, you are using a greater percentage of power to continuously heat the cathodes on a small lamp vs. a 3' or 4' lamp.

An F32T8 ballast will run F34T12 or F40 tubes....but there's no good reason to do this....the lamps will be underdriven and dim, and the instant-starting will reduce the life of the T12 especially in a bathroom where it's usually switched often.

It bothers me that the common knowledge is that T8 is brighter and better than T12 - yes, the surface brightness is, but actual lumens - not necessarily. They typically compare the F32T8SP41 with the F34T12CW or an F40 shoplight on an LPF home ballast. An F40T12SPX41 on a full-power magnetic ballast will outshine the F32T8...period.

A post-EPACT Watt-Miser is still a halophosphate, 60 CRI or lower lamp (cool white, warm white or lite-white). I have yet to see a triphosphor F34. The rule was either high CRI or low wattage...though now, F34's and F60's don't meet the efficiency standards which means the 4' and 8' lamps must have very good CRI. But due to the cost of triphosphors, deluxe halophosphate 89 CRI lamps have returned.

[GEsoftwhite100watts]

Yeah, trigger/rapid start ballasts (especially LPF ones) start unreliably in cold and/or if they aren't grounded. 
I have no extra T8 lamps, which is why as of the day I write this there are still F34T12s in that bathroom light.  They work, so honestly I see no reason to change them...
Yeah, even F40CWs on full-power ballasts are fairly bright; IMO bright enough. But SPX/ lamps will of course have better CRI and be brighter...
I thought halophosphate cool white has 62 CRI?
By deluxe halophosphor 89 CRI lamps do you mean cool white deluxe, etc?
Aren't the SP/ lamps triphosphor? Because if so trihosphor F40T12s do exist..

[Mike]

GE's ecolux f40 lamps are SP. they're definetly brighter than the sylvania cwp lamps.