running fluorescent light w/ one tube dead?


just curious if there are any long-term negative consequences to using a fluorescent fixture w/ a dead tube... specific application is my desk light, it's a (very old) Dazor "floating fixture" deal that well predates electronic ballasts. Uses two F15T8 tubes and I don't have any floating around. OK to use as is until I can get some or should I scavenge around the house for another lamp that will produce acceptable light? I anticipate being snowed in tomorrow so running to the store is not an option, I'll likely be splitting my time between being at my desk and shoveling.
nate
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Nate Nagel wrote:

You sure you have the correct tubes in it? As far as I know, electronic ballasts well predate T8 fluorescent tubes. T12 would be more likely if the fixture is really old.
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Pete C. wrote:

Pretty sure, there's a few of the same lights but with clamp bases floating around at work (presumably for back when they had draftsmen that used paper and pencils) and they use the same tubes.
Actually I "solved" the problem by remembering that there were some under counter lights in the kitchen that we never use and it turns out that they use the same size tubes, so I appropriated one of those until I can go out and get some more.
nate
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15 watt tubes came in both T8 and T12 sizes, with T8 being more common. 15 watt T8 is a long-standing and traditional size, probably dating back to the 1950's or so.
17 and 32 watt T8 are newer, but they predate common use of electronic ballasts. However, they were hardly used except with these modern electronic ballasts.
- Don Klipstein ( snipped-for-privacy@misty.com)
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If a 120V fixture has two F15T8 tubes, and one tube can light while the other is dead, and it well predates electronic ballasts:
Chances are it has two ballasts. That makes it safe to run only one bulb.
I would remove the dead bulb or the starter for it, unless the fixture has "manual start" (a "start" button and an "off" button and no starters). Beware of a dead bulb glowing only at its ends, even if only a dimmish orange, in a preheat fixture due to a stuck starter. I have known a ballast to catch fire from that.
- Don Klipstein ( snipped-for-privacy@misty.com)
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On Feb 10, 7:10pm, snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

You're correct in that it does have two ballasts. I did not realize this until after I posted, however. I'd just acquired said fixture when I posted, and one of the tubes that came with it died almost immediately. I discovered two separate ballasts in the base when I cleaned it up and gave it a coat of wax. It must be really old, because it apparently was used in a time when architects, draftsmen, etc. could smoke at their desks :/ I guess that explains the use of a coppery brown paint color, it hides the tar stains...

It does in fact have two buttons, and you have to hold the "on" button down for a second to "start" the tubes.
I just went ahead and ordered two new tubes for it, because it was easier than fighting my way to any of the local hardware stores, and also I could get "full spectrum" tubes online. As I said in my previous post, I found that the under cabinet lights in my kitchen used the same tubes, so I appropriated one of those as a temporary measure, so I've been able to keep using the desk lamp - but thanks for the reply in any case.
I take it that since you prefaced stating that it was safe to use by telling me that it probably had two ballasts, that that means it's generally a bad idea to use a fixture with multiple tubes on a single ballast with a bad tube?
nate
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N8N wrote:

check this out...
was just sitting at my desk, with the lamp we've been discussing lit... noticed that one of the ballasts was humming up a storm, enough to be not only noticeable but also mildly annoying. Disassembled base again, and removed both ballasts, thinking I'd insulate them from the metal with a little friction tape. Here one of them had one of its leads pinched between the core and the base of the lamp! I rearranged those wires, and also went ahead and put some friction tape on the top and bottom of the two ballasts. Nice and quiet now!
Wonder how many years it was buzzing? It's got a two-wire, non-polarized cord, so it has to have been quite a few! (which introduces the possibility that had it been left like that for another 50 years or so, someone might have gotten an unpleasant surprise, depending on exactly how it was wired...)
Now why, may you ask, am I messing with a probably 50 year old desk lamp? 'cause it's the one I wanted, and I'm too damn cheap to pay $300 plus for a new one, that's why.
nate
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Nate Nagel wrote:

IMHO you want a ballast tight against an enclosure to transfer heat out of the ballast, and don't want to do anything that would add thermal insulation to the ballast.
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wrote:

That fixture is in good shape for bad tubes.

Hope you get as much light as you want... Let us know if you do. Full spectrum fluorescents produce less light than ones with color rendering index mid-80's or less.

Now that I am putting some thought into that one...
Multiple tubes, single ballast, non-electronic ballast...
I can't think of any situation where a bad tube does not knock the other(s) out or dim, nor any situation that endangers the ballast.
If one of 2 tubes on a 2-tube ballast conks out and the other is very dim as a result, prlonged dim operation may cause extra wear on the good tube. If you see any orange end glow, prolonged operation that way is sometimes hard on the tube. One thing to watch for - if one tube is out and the other is dim, or if they are unequally very dim, the glowing/brighter one is not always the good one.
- Don Klipstein ( snipped-for-privacy@misty.com)
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On 02/14/2010 12:18 AM, Don Klipstein wrote:

Well, you thought I wouldn't remember, but I did :) the tubes arrived today, and they're just marked "F15 T8 5500K Full Spectrum" and they're actually rather attractive in terms of light color and how they make the crap on my desk appear, and they seem to be at least as bright as the old tubes of questionable age and functionality that I had before :)
Granted, I'm using two 15W tubes to illuminate a standard sized office desk, so it's gonna be bright no matter what.
nate

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