T 12 fluorescent light power draw

Say you have a T12 fixture with bad bulbs, black on the ends, not a glimmer of light emitted. Does it use the same or less power then the same fixture with good bulbs? The ballast must still use power even with bad bulbs.

I 'think' they use the same power as one that is lit, just the gas is not reacting

If the gas is not lit it is not ionized. If it is not ionized it does not conduct current. So no an unlit bulb is not using power. The ballast is not a perfect inductor. There is some small resistive component, it still gets warm, but this is minimal.


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WHile you are correct I am sure, there is current flowing, 'dead' bulbs frequently are glowing at the ends, I am just unsure of the percentage that is flowing

At my last job we had a warehouse full of old florescent lights. They were all the old, non electronic ballasts, some as much as 20, 30, or 40 years old. Many of them did not come on. Some circuits which were a dozen or more lights only had one or two that actually lit up. I asked our electrician about the power usage and he said that they did not use full power if they were not actually on or if there were no bulbs.

I can personally attest that some of the ballasts were getting hot. Others not. I took some current measurements with a clamp on meter and did find that they drew some current, but not the full amount that the bulbs should have. It varied from one circuit to the next. I tried to keep as many of them turned off as possible.

I do not know about the electronic ballasts. '

BTW, just saying "T12" fluorescents does not nail it down very well. "T12" stands for Tubular and 12/8 inch (1.5 inches). That is all it means. It says absolutely nothing about the technology inside that tubular lamp. There are many, many combinations of bulbs and ballasts and some of them will behave a lot different than others. Grab a Grainger or McMaster catalog and read about the many types of ballasts and bulbs. Some of the combinations of ballast and bulb are not even recommended.

There are two types of T12 lamps, rapid start and instant start. Rapid starts have filaments on each end to ionize the mercury in the tube and do use power. That's the reddish glow at the end of the tubes. The tubes and fixtures are identified by having two pins on each end of the tube. Same for the fixture, the tombstones have two openings. Instant start tubes only have one pin on each end. The have no filaments. Magnet ballasts are special design transformers that provide a high voltage to start the tube, then they regulate the current. Rapid start ballasts also provide the filament current. Electronic ballasts do the same thing, they use electronics instead of magnetics.

As to current being drawn, a fully functional fixture will draw current for the ballast, be it magnetic or electronic, filament current if it is rapid start and lamp current. Lamp current is the is the current that maintains the arc inside the tube which provides the light. Instant start do the same thing without the filament current.

So to answer your question, a fixture without lamps will draw a small amount for the ballast. A fixture with a dead lamp may draw additional current if it has filaments.

Tom

And a bad ballast can draw enough enough current to get hot enough to melt, produce smoke, and in severs cases even start a fire. This does not happen instantly, it comes on gradually with ever increasing amounts of current draw.

There are many ways that a fluorescent lamp can fail and consume current.

If you have a fluorescent fixture that is not producing it's full measure of light you should:

1. Fix it
2. Replace it, preferable with an LED style light
3. Dis connect it
4. Rewire it for replacement LED tubes.

I choose the fourth choice for about 16 T12 fixtures in my house and garage. It took 39 LED tubes. In spite of the fact that the LED lamps that I purchased would run with or without the old ballasts, I removed and tossed away ALL the ballasts. They are more efficient that way and I don't have to worry about the old ballasts going bad. I have had zero problems in the two years since making that conversion. And I have probably saved most of the cost of the LED bulbs by now. The light is great and in many places I used 3 LED tubes in place of 4 of the original fluorescents. The light is BETTER everywhere, especially in my shop.

LEDs rock! Win, win, win!

TDegenhart said:

There are two types of T12 lamps, rapid start and instant start. Rapid starts have filaments on each end to ionize the mercury in the tube and do use power. That's the reddish glow at the end of the tubes. The tubes and fixtures are identified by having two pins on each end of the tube. Same for the fixture, the tombstones have two openings. Instant start tubes only have one pin on each end. The have no filaments. Magnet ballasts are special design transformers that provide a high voltage to start the tube, then they regulate the current. Rapid start ballasts also provide the filament current. Electronic ballasts do the same thing, they use electronics instead of magnetics.

As to current being drawn, a fully functional fixture will draw current for the ballast, be it magnetic or electronic, filament current if it is rapid start and lamp current. Lamp current is the is the current that maintains the arc inside the tube which provides the light. Instant start do the same thing without the filament current.

So to answer your question, a fixture without lamps will draw a small amount for the ballast. A fixture with a dead lamp may draw additional current if it has filaments.

Tom

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