Am I buying the wrong kind of fluorescent lamp tube?

Factual Questions
1

I have a drop ceiling with recessed fluorescent lamp fixtures. The fixtures take 4 tubes of the 48" size. These fixtures were bought new about 12 or 15 years ago IIRC.

I’m trying to replace lamps that have blown out. I had a few old lamps removed from other fixtures, and when I put those in, they seem to work fine.

But I just bought a new 10-pack of tubes at Home Depot, and tried several of them in several of the fixtures. None of them work. They glow very faintly red at the ends and perhaps have the weakest barely perceptible flicker over their length, and that’s it.

The Wikipedia article on fluorescent lamps suggests that they come in a wide variety of more or less incompatible types, electrically. But there didn’t seem to be any different kinds of 48" lamps available in the store, other than different shades (cool, daylight, warm) and different lifetime (24000 hour, 30000 hour, 40000 hour). Am I getting the wrong kind somehow?

I think the fixtures must be good because the old working lamps I move around work in every location I try. Also, there is no humming noise to suggest a bad ballast. These fixtures do not have the little replaceable can that controls starting. I can’t see any labels anywhere on the fixtures except for a UL sticker about safety.

Can anyone help me out?

2

Are you matching the wattage of the tubes to the ballast wattage? Tubes and ballasts work best (and last longest) when the wattages are matched. A small mismatch either way won’t make a huge difference, but trying to run, say, a 40-watt tube on a 10-watt ballast might cause problems similar to what you’re seeing. Other possibilities exist, but I haven’t time to go through all of them at the moment.

3

All I can guess from afar is you got something like F34-T12 tubes instead of F40-T12’s.

A fixture of that age may or may not be flexible enough to work properly with the “energy saving” F34-T12 tubes that are common now. The solution is to either find “old style” F40’s or swap out the ballasts to accommodate today’s tubes.

4

You might have bought T-8 tubes instead of the T-12 tubes that were the old standards. The T-8 tubes need the newer electronic ballasts and you probably don’t have those in your older fixtures.

5

I don’t think T-8s would fit in an older fixture built for T-12s, but in any case you’d know if you had bought T-8s as they are much slimmer bulbs.

I’ve never heard of energy-saving T-12s that wouldn’t work in a standard T-12 fixture, but I suppose if the lamp is ancient enough, anything’s possible.

6

They are physically interchangable.

See here for more information.

7

>Are you matching the wattage of the tubes to the ballast wattage?

All say 40 W.
>All I can guess from afar is you got something like F34-T12 tubes instead of F40-T12’s.

Ah! I had F40SHOP lamps and now have F32T8/ADV84I/XEW ALTO lamps, according to the fine lettering on the ends of the lamps.
>I don’t think T-8s would fit in an older fixture built for T-12s, but in any case you’d know if you had bought T-8s as they are much slimmer bulbs.

The new lamps are slimmer. But they fit the old fixtures just fine.
>swap out the ballasts
How hard is that? It took about 5 minutes to get to see the ballast, as the ceiling these are in has very limited space. I can’t even remove or install a tile because the overhead clearance is so small. Are ballasts supposed to be interchangeable, or am I likely to have to replace all the ceiling assemblies and take down much of the ceiling in the process?

8

Many T8 lamps will fit where T12 were previously installed, so long as they both are designed to fit the ‘medium bipin G13’ lampholder.

Whether you have to replace ballasts is a qualified maybe. I’ve relamped many older fixtures with energy saver lamps and had them work fine. Assuming you install two new lamps and it doesn’t operate, and you have no other issues such as broken lampholders, then ballast(s) are the next step.

Typical troffers have a raised hump-shaped piece of sheet metal running parallel to the lamps, located between the two pairs. Beneath this sheet metal live the ballast(s). First, remove power from the circuit. You don’t say if this is home or industrial, but this style fixture can be operated with line voltages from 120 to 277 VAC, and you do NOT want to get bitten by 277!

After the fixture is de-energized, remove the two lamps closest to the center ridge. Squeeze the sheet metal towards the centerline with your hands, close to the upper plane of the reflector to unclip the ballast cover from the reflector. Once you’ve unclipped both retainers on one side, you can then carefully remove the ballast cover. It may contain many dead bugs, and/or so oily looking goo. Goo escapes a ballast which has gone to meet its maker.

You will find either one or two ballasts. Copy the numbers off of them-manufacturer could be Advance, MagneTek, Triad, or others. The only change you’ll be making will be for the lamp(s) powered. The label on the existing will state it is good for 2 or 4 F40T12 lamps at whatever line voltage the fixture is supplied with. When you go to the electrical supply store, line voltage, number of lamps, and physical size of the replacement ballast(s) must match, but get units designed to work with F32 energy saver lamps.

To replace the ballast(s) in an existing fixture, I clip the red, blue, and yellow wires about 3" from the ballast. The black and white are disconnected at the wire nuts. Strip the thin colored wires back about 3/8". After the replacement ballast is installed, attach the lamp wires, matching colors. To make the connections, use small blue wire nuts, the next smaller size than orange. Get a box at the supply house if you don’t have any. Reattach line black and white, and loosely twist the wire bundle together in a manner so as to prevent pinching any conductors when you reinstall the ballast cover.

Relamp, power the fixture, and move on to the next. Good luck

9

I bought a box of 12 T-8 lamps for my office about 6 months ago. The wattage matched the old T-12 bulbs, so I figured they would be fine. They lit up and I replaced all of the dead tubes with the T-8’s.

Within 3 weeks, all of the new T-8’s were dead. The link cited by GaryM a few posts up shows that the T-12’s and T-8’s are physically interchangeable…they’re the same length and the pins on the end are the same…but the newer T-8’s require the electronic ballast rather than the older magnetic ballast.

Maybe my ballasts were newer, but not the newest electronic ballasts and the OP has a really ancient ballast that can’t handle them at all.

10

Although the pins will fit, in general you should not operate T8 lamps in a fixture with a ballast designed to operate T12 lamps. Although they frequently will work (for a while), the lamps will generally burn out far earlier than intended. It likely invalidates the UL rating of your fixture, as well.

T12 lamps will be 1.5 " in diameter (12 eighths of an inch). T8 lamps are one inch in diameter (8 eigths of an inch). T8 lamps have a higher efficacy than T12s, meaning you get more lumen output per Watt of power input.

Your ballasts are likely designed to power F40T12 lamps, and are likely magnetic ballasts. Because they were fairly inefficient, manufacture of F40T12 lamps was outlawed a few years back (except for a few specialty applications.) They have been replaced by F34T12 lamps as the new standard.

It will be far easier to just say that your investment in the T8 lamps was a mistake, hang it up, and go get some F34T12 lamps to use with your existing ballasts and fixtures, unless you have reason to believe that your ballasts are the real problem. If that’s the case, I’d go ahead and install electronic ballasts and use T8 lamps. Ignore the stuff from the earlier-cited site saying that T5’s are the way to go. Although they do have a higher efficacy, they are very bright point sources of light, and I don’t think you’d be pleased by the results of trying to use T5’s in a one-to-one replacement of what you have now. They’re better used in direct/indirect fixtures.

Looking a few years down the line, T12 are also on their way to being phased out due to the Energy Policy Act of 2005. Unless they come up with a way to dramatically improve the ballast efficiency within the next couple of years, manufacture of ballasts to operate the F34T12 lamps will be prohibited after July 2010. I wouldn’t get too worried about that at this point, however, as most ballasts have a life expectancy of around 50,000 hours or so.