Fluorescent bulb acting up

Joined
Sep 9, 2019
Location
Leavenworth Kansas
so the other day I was going through Qs for our show, and noticed this fluorescent light acting weird, sometimes it works but sometimes it doesn’t. Now we did work on this last year because it wasn’t working, so we replaced the ballast and the light last year which in my opinion I don’t think it could have gone out that fast. Could it possibly be a short? Ever since our school had a renovation in 2009 this light fixture has been giving us problems. Any clue on what it could possibly be?
 

RonHebbard

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Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
so the other day I was going through Qs for our show, and noticed this fluorescent light acting weird, sometimes it works but sometimes it doesn’t. Now we did work on this last year because it wasn’t working, so we replaced the ballast and the light last year which in my opinion I don’t think it could have gone out that fast. Could it possibly be a short? Ever since our school had a renovation in 2009 this light fixture has been giving us problems. Any clue on what it could possibly be?
@Christian Lake Is the fluorescent in question a work light normally powered on an off by a standard wall switch or is it being powered via a non-dim or dimmer from your performance lighting system? If the latter, try adding a purely resistive load in parallel with the supply to the fluorescent.
Fluorescent fixtures contain ballasts. Decades ago, the ballasts would've been wire wound around a magnetic core, creating a highly inductive load. This was no problem for wall switches but neither solid state non-dims nor solid state dimmers dealt well with highly inductive loads. In modern times, many ballasts are electronic rather than simply wire wound around cores; either way, solid state non-dims or dimmers will not deal well with them.

Pay attention to your non-dim or dimmer's load ratings and DO NOT exceed their ratings.
Purely resistive dummy loads could be: A 40, 60 or 100 watt, 120 volt lamp or a toaster or heating pad.
If you're using a lamp, you may need to locate it off stage, or least mask it so it doesn't distract from your lighting on stage.
If you're using a toaster, be aware it may decide your toast is ready and switch off, thus leaving you without your dummy load.
If using a toaster, be VERY careful the toaster doesn't consume more watts than your non-dim or dimmer is rated for.
Toodleoo!
Ron Hebbard
 

microstar

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Joined
Jan 19, 2014
Location
Lawton, OK
Yeah but what’s weird about it is that if it comes on first before the rest do then it doesn’t turn on but if it comes on exactly when the others come on it works. We’ve replaced this ballast about 10 times already. Everything in that fixture is brand new
It's obvious that these are on a dimmer, so they need to have "dimmable ballasts". Chances are the one that is misbehaving either doesn't have a dimmable ballast or if it does, it is not an exact match to all the others that do work properly. Or I could be totally wrong.
 

RonHebbard

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Joined
Jun 12, 2004
Location
Waterdown, ON, CA

Mac Hosehead

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Sep 10, 2014
Location
Shark Tank
Since the fixture is running from a dimmer rack, I might assume that it has a 2-wire dimmable ballast. Ballasts of this type can vary as to how well they perform when dimmed. I would also have to assume that the current ballast in the fixture was not replaced with the same ballast as the original. ETC used to have a sheet that showed which ballasts worked better with their systems but I cannot find it. One ballast I believe I can recall working well was this:
https://www.iballast.com/media/pdf/advance/Mark-10-powerline-brochure-v1.pdf

Other issues can affect dimming performance such as good grounding. ETC also recommended running new lamps at full for 100 hours before normal use.
 
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JD

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Joined
Jan 1, 2005
Location
North Wales PA
Dimmable Florescents are a tricky business. Unless all your ballasts are of the same type, hopefully from the same run, and your lamps are age matched from the same batch, then getting a real good match will be a problem.
There are variances in tube gassing that may change the point where they strike-on. In addition, even ballasts of the same part number may vary in construction year-to-year.
There are usually two circuits feeding the ballast, one is on all the time and preheats the cathodes as soon as it sees voltage on the second circuit, which is the one from the dimmer. The actual design of the circuit varies depending on the manufacturer.
Putting a small (100 watt) ghost load on the circuit that is dimmed may prevent misfires.
 
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Les

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Joined
Feb 24, 2004
Location
DFW, Tx.
Could it possibly have something to do with how all of the fluorescents don’t turn off at the same exact time?
That's a symptom of the same problem. Once you start relamping, replacing ballasts, etc; it seems like no two fluorescent fixtures will ever dim the same way again. Read JD's post again.

I know why some schools have fluorescent houselights (cost, efficiency, labor) but it still makes me cringe. They never look good, even when operating correctly.