Creating a "bad ballast" effect

Preston Herrick · March 30, 2004

I need to create the effect of the ballast going out in an overhead flourescent fixture - you know, flickering on and off in a random fashion. I don't have the luxury of renting a flicker unit and don't know for sure if it would even work with that type of light.

Anyone have any DIY ideas?

Mitch Gross · March 30, 2004

It's possible that you could put the ballast on a dimmer and this would cause it to flicker, but be prepared to destroy both the ballast and dimmer in the process. Not a big deal as they are both very cheap, maybe $15 total. KinoFlo does make a fluorescent flicker box that you can use for this, but as you say, it is a rental.

Phil Rhodes · March 30, 2004

Hi,

1) Switch, and get someone to flick it on and off. Laborious, but a highly controllable effect.

2) Variac. You can't use a triac dimmer - the ballast's inductive kick will destroy it - but if you can get a variable mains transformer, you can probably find the point where it'll flicker of its own accord. This can require constant adjustment as the ballast and starter warm up.

3) One of the hardier kinds of triac dimmer, generally designed for theatrical lighting, and program a digital lighting controller to ramp it up and down in a pseudo-random pattern. The rental company will know which of their dimmers is most suitable for this kind of rough duty. Possibly more expensive to rent than a flicker box, though.

Almost any method you can use to make a tube do this will be very hard on the components of the system, mainly the tube and starter, and may cause premature failure. However, you can buy a ballast, starter and tube so cheaply that it probably isn't that much of a consideration. Also, don't even think about doing it with a Kino-Flo - not only will the variac trick not work (the switching ballast will try to keep the tube current up until the point where it just drops out) but you will very quickly wreck the tube and ballast due to the slightly oddball way they start. I'm presuming it probably doesn't matter if your light has some mains flicker when it's on, anyway, so you can use a basic iron ballast type.

Phil

Phil Rhodes · March 30, 2004

Hi,

Re Mitch's reply, while stury theatrical triac dimmers have been shown (by me) to stand fluorescent ballasts for quite some time, I have tried it with the cheapo wall-mounting types you'd use for incandescent lightbulbs, and you should be aware that they can last a matter of seconds under this kind of (mis) treatment (generally the pass SCR fails). Highly liable to fail halfway through your shoot, plus they can produce annoying, non-interesting flicker effects with certain ballasts.

Phil

Preston Herrick · March 31, 2004

Thanks guys. Since I don't have a Variac I think I'll take the least destructive route and try Phils suggestion with finger power. I was afraid the units might not turn on fast enough for the right effect but I tried it with the garden variety overheads in my shop and they respond fine. I may just build a momentary push button switch to run the power through and let a grip have at it.