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Making a fluorescent flicker and flash

Discussion in 'Lighting and Electrics' started by Reggie, Jun 15, 2004.

  1. Reggie

    Reggie Member

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    I thought I had read somewhere how you can make a flouro fixture flicker on and off as if it has a bad bulb or ballast. I recall it being done with a dimmer. I tried this with a two tube 40w shop light and an SCR dimmer. I tried several fixtures, all had transformer type ballasts, some had starters, but had no success. The fixture would dim somewhat then go out as I chopped the voltage. The tubes would come back on near the the top of the dimmers range. I could never get the effect of a bad bulb or fixture randomly flashing on and off or never fully lighting. I need to do this for a location shoot in a basement. I don't think having someone switch it on and off would give the same effect, that would kind of be all or nothing. Brings some old tubes to a location and installing them is too unpredictable. Any ideas??
     
  2. bdesmond

    bdesmond Active Member

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    There are special dimmers for flourescents, and with some racks, you can set a dimmer profile to match. This is not something (flourescents) that I'm veyr knowledgeable about, though.

    If I were doing this with equipment onhand, I would probably set a dimmer to non-dim, and program a flicker type effect.
     
  3. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Again - not an expert on this but I was once told that dual fixtures were developed mainly to reduce the amount of flickering that single fixtures are prone to. Perhaps if you tried with a single fixture you may have some luck.
     
  4. Reggie

    Reggie Member

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    Re: Making a fluorescent flicker and flash - Take two

    I'l try explaining this again. I'm not doing this in a theatre or even in much of a controlled environment. I working "on location" with a film crew. We (I) don't have a dimmer rack accessable. Anyway I'm not trying to dim the fixture. I am trying to trick the ballast and/or starter into thinking it has to restart the lamp again and again. I want the fixture to achieve partial brightness then go out and repeat this pseudo random cycle again. Simple dimming or switching it on and off won't accomplish this. I don't have access a "Magic Gadget" or flicker box (which is really meant for incandescant lamps).
     
  5. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    What is your time frame for this Reggie?

    I may be able to do some testing over the weekend but I need to know how much access and ability are you going to have when it comes to tinkering with the electrics?
     
  6. ship

    ship Senior Team Emeritus Premium Member

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    This it would seem to be a large problem in that short of actually mal-functioning ballasts to which I had professionally even just thru out the bad ballast to this week on such a real life fixture, I'm at a loss. Ron! ya out there?

    Of interest beyond fluorescent starters being of the improper type might be a ballast of the improper type in simulating the attempt to start the lamp but being either too much voltage or too little to actually ignight the arc thus the intent. Stagecraft as a forum might also have some ideal but otherwise I as a humble electrician type might think it necessary to experiment either with fluorescent starters not sufficient to strike the arc or maintain it, or ballests in it's lack of need for in striking and maintaining it's arc. In the end it's a wattage issue no matter how many lamps in attempted to start by the ballast or starter not the number of individual lamp fixtures. In other words, short of the proper balllast to control the lamps but too old to ignight them as per the movie effect you intent, I expect the solution is going to be in either too much voltage for the lamp or too little voltage to them. Too much voltage while it might strike the briliant arc of light might possibly not have enough at the period of time to continue that arc during the starting process, otherwise too little voltage/amperage supplied to the arc will maintain that constant attempt to strike the arc but not be sufficient to maintain it. Given a single 40w. lamp for instance, perhaps a 32w lamp ballast will be sufficient to constantly try to ignight it but not to stabalize the arc within the lamp. Given that does not work, perhaps the next smaller ballast will try with all it's might but not be sufficient in striking the arc.

    Hope it helps, such a science of bad ballasts is very troublesome to do in an intended type of way. While phase harmonics might destry a ballast and lamp, it's more of a long term effort. I think it more safe in attempting lower wattage ballasts for the load intended. Good luck and post your results very specificially to help others in the future with this attempt.
     
  7. Reggie

    Reggie Member

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    Mayhem,
    In reply, as of today, I have 8 more days. I had found a post on a cinematraphy board. But their idea of using a dimmer (SCR) type did work with any the fixtures I tested. Maybe I try mis-matching the starter to the ballast.
     
  8. ricc0luke

    ricc0luke Active Member

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    On accident we had fluorescents flickering like what you want once...

    We were using 4 and 2 foot blacklights... they were all single buld fixtures though... and blacklights though.... but in theroy it should work.

    We just had them on a dimmer pluged into our board.... we discovered it on accident when we left the slider half up!
     
  9. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Hi Reggie,

    Just wondering if you have access to a variac? I tested a few fluro fixtures today ranging from single 4' batons to a 4 tube x-ray viewer. Managed to get some cool looking flickers very easily with the variac. I found that fixtures with multiple tubes actually created some nice effects as some tubes would behave differently to the others (due to age and tolerance differences)

    The advantage of using a variac is that you can make the fluro operate normally if desired and there is no need to change the starter or the ballast.

    For anyone reading this post that are not familiar with a variac. It differs from a dimmer in that you are actually varying the voltage with a variac. It is basically a large mains voltage variable resister. (I did a very quick google search and one page with pictures is http://variac.com/staco_Variable_Transformer_Map.htm)

    I found the best results occurred at around 75-85% of mains voltage, in this case 180VAC to 200VAC (we use 240VAC)

    Hope that this is helpful
     
  10. Reggie

    Reggie Member

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    Thanks Mayhem! I have a 2k Variac, but didn't consider trying it since the writeup on flickering flourcesant light indicated that they used an SCR type dimmer. I'll give it a try and post the result.
     
  11. Reggie

    Reggie Member

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    Mayhem,
    Tried a vaiac. It was not any more successsful at producing the effect I want than an SCR dimmer was. I think I will have to dedicate a person to "dial twiddling" during the shoot. Thanks for the suggestion though.
     
  12. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Yes - I found that the voltage needed to be varied (within that 75-85% range) to get the tube to fire, flicker and then go out. I found the effect fairly easy to create and control in this manner.

    I apologise for not making this control requirement clearer in my earlier post, rather than stating the range.

    Will the person get credit as "Fluorescent lamp effects variac control dial twiddler" ? I mean how cool would that look an a resume 8)

    I hope that you will get the end result and please let me know how the shoot goes.
     
  13. Reggie

    Reggie Member

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    Sad, but true

    After all the effort put in to achieve this lighting effect, the scene was cut due to time constraints. It was one of the last scenes of the day and after putting in over 14 hours, the Director of Photography decided to simplify the scene, including the lighting. So while the effect was set up and demonstrated, it was not used.

    Thanks to everyone for all the suggestions.
     

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