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Lighting questions

poppi's picture

I am not an electrician so bear with me.

Our facility has a large number of ceiling light fixtures with 3 each FT40T12 bulbs. I know that I will soon need to convert these to T8 bulbs and change out the ballasts. My questions:

1) The present fixtures each have 2 ballasts, 1 for a single bulb and 1 for 2 bulbs. Why do the two circuits require different ballasts?

2) Will the new T8 bulbs also require two different ballasts?

3) Will the T8 bulbs work in the older T12 two pin sockets?

Thank you



You can get ballasts for 4 ft (post #207487, reply #1 of 11)

You can get electronic ballasts for 4 ft t8 bulbs that operate 2 or 4 bulbs.  If you get all 4 bulb ballasts, you simply cap unused blue wire  to run  3 bulbs.

You only need one ballast per fixture.

Someone on Ebay almost always has the 4 bulb ballasts for under $10 each, and I usually wait till I find ten at a time for $4 a ballast with free shipping.   Since  you say 'large number',  I have seen an offer of a pallet full of ballasts (like 200 or so!) for under $3 each. 


PS: same sockets

PPS, the old ballast will also run the T8, but electronic ballasts are lighter, quiet, and will same their cost in electricity in only a year or so. 

old ballast (post #207487, reply #3 of 11)

 A magnetic ballast will light a T8 bulb, but not well Art.  They will noisy and burn out prematurely.

Are you buying multi-voltage ballst at $4 each or just the 120v flavor.  We buy the dual voltage type in unit quantities for around $8 each.  We date stamp all of our installs and expect warrenty replacement ballast for premature failures.  Can yo get that on e-bay?

It is interesting that the 2 (post #207487, reply #4 of 11)

It is interesting that the 2 bulb ballasts on ebay are mostly 120-277 universal voltage, the 4-bulb one I've seen for $4 are 120V only as you suspected, the $10 ones are generally universal. 

I do cheat in some sheds (code??, what's that) and use Motorola 4 light 277V ballasts across 240V.  Did this only after dissassemby of one of the ballasts (open circuit board, no potting) and veirfying that the application was safe (white wire as isolated as the black, a fully floating switching power supply).  Of course, standard disclaimer, not recommended for a diy that does not know how to design an electronic power supply.

I have not researched why T8 are now preferred, other than lower Hg.  From 40 years ago when I did 400Hz lighting on aircraft,  the textbooks then said 1.5" dia produced the best efficiency,  which is why T12 ruled for so many years.  The T4 and T5 used on old airplanes were for space, mostly just a series capacitor for the 'ballast'.  Everything electronic ballasts now of course.     

I think the combo of (post #207487, reply #6 of 11)

I think the combo of electronic ballasts and improved phosphors made the T8 a better performer.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

$$$ (post #207487, reply #10 of 11)

Energy codes have been changing over the last 10 years.  The e-ballast and T8 bulbs reduce energy usage by roughly 30% in our experience.  Bulb temperatures (color) have been improving for more years than that.  The higher temp. bulbs in the T8 size produce more lumins than the T12's that have been in use for so long.  More light, less energy, code compliance, and tax credits are the drivers.

New construction is covered extensively in the energy code and requires either occupancy sensors and timers or both to pass permiting requirements.  On remodels, grandfathered buildings are of course exempt, but  most larger companies weigh the energy saving and tax credits to justify the cost.  Long term I believe the switch over justifies itself, but it is hard to sell in a weak ecconomy.  I think we will eventually see big brother ram energy code compliance down everones throat by insisting that all building be brought into the fold either when any remodeling is done, or by apply a must meet  by date to the code.  Then it won't matter if the business is large or small, they will have to comply.

lighting (post #207487, reply #2 of 11)

The three bulb fixture is pretty common in commecial aplications. The ballast arrangment you mentioned is also common.

Now I will speculate that the voltage is likely 277V.  Because you described the place as a facility.

Conversion to the T8 bulb means you are going to electronic ballast.  They now come standard for either voltage in the same ballast.  You will save $$ on you energy cost with the conversion and may qualify for a tax credit if it is still available.

You will also find the the work environment be a lot less noisey.  The elctronic ballest does away with the old 60 cycyle hum you got from magnetic balast.

There may be a single e-ballast that can drive three T8 bulbs if memory serves me correctly.  Call a lighting supply house and get a rep out to see what you have and what you need.  We started doing our conversion years ago. Kind of piece meal for a few years, then we got some capital money and changed out every fixture in our facility.  With the correct temperature bulbs we were able to convert to two bulb fixtures and actually incresed the lumins of light per square foot.  The tax credit was a big driver in us getting the capital funds to do the project.  Be sure to check it out.

I think the use of 2 ballasts (post #207487, reply #5 of 11)

I think the use of 2 ballasts is popular because it keeps a tube or more lit in the event of a ballast failure.

I suspect that the main (post #207487, reply #7 of 11)

I suspect that the main advantage of the 3-lamp, 2-ballast fixture is that it can be placed on two switches, for 3-level lighting.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Thats true also.  But even if (post #207487, reply #8 of 11)

Thats true also.  But even if there is only one switch there is an advantage to two ballasts.

ballast (post #207487, reply #9 of 11)

I don't know what the original intent was.

In my experience most any electrician will change both ballast when one goes bad,  Same thing with the bulbs. If I'm going to climb a ladder and change out ballast I am only going to do it once.  Cost of the additional ballast and new bulbs is less tha 50% of the cost of the labor.

you might want to check out the led replacements (post #207487, reply #11 of 11)

I've gotten several fliers in my mail from companies that are making led replacements for flourescent tube lighting. 

The "bulbs" are far more expensive, but have a longer life at a higher efficiency. They typically work on 120-Volt systems without ballasts.  And, at least two have been designed to work on 240 volt systems without ballasts.  Which means you save the cost of the ballasts, and long term maintenance of the ballasts and the bulbs. 

Unortunately, we made the switch to T8 bulbs and electronic ballasts just two years ago, by leveraging a power company rebate program, so they don't pencil in for us right now. 

I may look at them for the house, or home shop next time I have to reballast there.  They don't have the low temp issues that flourescents do.