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Fluorescent Flicker/Strobe Problem


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#1 James Brown

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Posted 23 March 2007 - 08:30 AM

Hi,

I'm in the process of pre-lighting a set for a new series. We have encountered an unusual problem with some fluorescents that have been mounted vertical on support beams. They are gelled, in a diffuser, and will be in shot.

They are all on the same live circuit (4 in total) and after about 5-10 minutes of being active they start to strobe slightly. A slight pulse that eventually gets worse. After trying to eliminate all possibilities (the tubes, the power source, the unit itself) they were still pulsing. The in-house electrician came in and said that turning the tubes upside down should fix it as it's probably a gas buildup. Sadly it still strobes and the electricians are out of answers. Has anyone had this problem?

Regards, James.
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#2 Richard Andrewski

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Posted 23 March 2007 - 05:55 PM

Yes, I've seen the problem before. Its a ballast problem one way or another. Tubes don't flicker by themselves. They are driven by a ballast--whether the ballast is built-in like a spiral CFL type or a separate ballast like anything ranging from a Home Depot shoplight to a professional video/film fixture. I'd look at totally replacing the fixture and make sure you have a good and reliable electronic ballast. They just don't flicker when they're of good quality. The only other reason it might happen is the power coming in. If the power has problems, even the best electronic ballast may not be able to maintain the normal discharge in the tubes and intermittent flickering will result.
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#3 James Brown

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Posted 23 March 2007 - 06:50 PM

Hi Richard.

The Ballast(s) are all new and we have used the same brand from the same batch (except in four foot) in many other areas of the set. These have been placed vertical which is the only difference. The power coming in should be fine as other fluorescent fixtures we have on the same circuit do not have the this problem. I tried to run a mains feed directly from another circuit and still had the same problem. That's why it's got us all stumped. Could it be anything else?
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#4 Michael Nash

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Posted 24 March 2007 - 01:23 AM

I tried to run a mains feed directly from another circuit and still had the same problem. That's why it's got us all stumped. Could it be anything else?


You said they're all on the same circuit -- every time I've had a ballast problem with commercial fluoro's it's been from low voltage. If you cube tap too many "touchy" ballasts together they'll start to fail. Have your electricians meter the voltage at each unit, and see if that's the culprit.
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#5 David Auner aac

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Posted 24 March 2007 - 04:43 AM

Hi James,
probably a silly question: do they strobe in a horizontal position as well?

Cheers, Dave
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#6 Hal Smith

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Posted 24 March 2007 - 05:57 AM

(except in four foot) in many other areas of the set. These have been placed vertical which is the only difference...............

I assume the others are 8' fixtures? Magnetic ballasts? How warm/cold is the set? It's getting to be fall down your way and I'm wondering if there's some sort of negative effect with vertical 8's if the bottom of the bulb runs too cold. My shop is lit with 8' dual fixtures and I've got a brand new spare that I'd be willing to try running vertical to see if this is a universal effect. I can't think of a place where I've seen 8' fixtures installed vertically so maybe you've uncovered a can of worms!
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#7 James Brown

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Posted 24 March 2007 - 07:09 AM

Hi,

>I assume the others are 8' fixtures?

Sorry maybe a typo. The ones vertical are 2 Foot. There is four all together. Two linked together and each run into a circuit in the roof. They are fine for about 5-10 minutes and then start pulsing. But they all start at different times. Then turning the tubes upside down they wait about 10 minutes then start pulsing. The weirdest thing is (which i forgot to mention) we also have 2 x 4' and 2 x 2' in a light box at the end of the room running off a completely different circuit and only one of these four tubes pulses/strobes. The gaffer nor the electrician understands what the problem is.

>Have your electricians meter the voltage at each unit, and see if that's the culprit.

Thanks Michael, i will get try that 1st thing monday morning.

This all happened friday morning before a make up test so we only had about an hour to try and fix the problem.

>probably a silly question: do they strobe in a horizontal position as well

Havent had the time to try these exact units horizontal because they have been fixed to the pillar already. This shouldn't be a problem though as we have mounted a many fluros vertical without a problem.

James
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#8 David Auner aac

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Posted 24 March 2007 - 11:17 AM

Havent had the time to try these exact units horizontal because they have been fixed to the pillar already. This shouldn't be a problem though as we have mounted a many fluros vertical without a problem.


Yes, but I have seen some fluros flicker strangely when in vertical. These were cheap home depot types though...

Cheers, Dave
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#9 Richard Andrewski

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Posted 25 March 2007 - 03:40 PM

Strange, I've never seen a problem with flickering based on vertical / horizontal but with some types like the 2G11 Biax you can have some color temp variations based on whether you have the base up or down in a vertical position. It seems those type lamps really like to be mounted with the base up if you mount them vertically. This is because all their connections are at the base where the cathodes are. In the type lamps your talking about the cathodes are at each end so there shouldn't be a problem like that.

I wouldn't totally rule out a bad socket or two though at this point. Remember, these things operate off one ballast for 2, 3 and sometimes 4 tubes. If one tube or socket in the circuit is bad, it can affect the others. Sometimes the fixture won't even fire with a bad tube or socket.

I don't remember, did you try replacing both tubes yet? Other than that voltage would be the next best thing to checkout.

Edited by Richard Andrewski, 25 March 2007 - 03:42 PM.

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#10 James Brown

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Posted 26 March 2007 - 02:47 AM

Hi,

You would not believe what happened. After last week's mad rush of changing tubes, power supply and ballast's and still not being able to rectify the problem. I walked in this morning turned, them on and left the room for a few hours. I came back and everything was fine, no pulsing, no anything. This doesn't really help the cause because if it happens again i'm not sure how to solve it. It could have been low voltage but that does not explain why the other soft boxes were not pulsing.

Anyway, thanks all for your help.

Regards, James.
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