How to achieve flicker on fluorescent lights?

[Michael Totten]

The director wants the fluorescent work lights to flicker on and off... how is this achieved ?

A flicker box ? I'm concerned that because fluorescent bulbs take a moment to strike that a flicker box might not work.

 

[David W. Jones]

choose an out of sync frame rate?

 

[Reinhold R.]

@David: I think he's talking about a more irregular, creepy, somebody-is-going-to-die-in-a-minute flicker.

To my knowledge this can be achieved by using a conventional tungsten dimmer switch, one that is not designed to work with fluorescent bulbs. At a certain voltage the bulb should start to flicker.

 

[Michael Totten]

@David: I think he's talking about a more irregular, creepy, somebody-is-going-to-die-in-a-minute flicker.

To my knowledge this can be achieved by using a conventional tungsten dimmer switch, one that is not designed to work with fluorescent bulbs. At a certain voltage the bulb should start to flicker.

David.
yeah I'm looking for the creepy irregular look. I'm going to try the dimmer today. thanks for the info... : )

 

[Nicolò Rebughini]

The regular dimmer used for tungsten won't work with fluorescent because that kind of lamp is not based on the principle of incandescence. Maybe dimmed at a certain level could produce something interesting.

A way that I know that works has been taught me by a light I have at home. Just find a way to make rapid on/off switching and you may be good to go. I say this because one time at home I mistakenly not pressed all the way down the switch and it stayed in a status of uncertainty where it made a loud buzz (not sounded safe) and the light had just the look you want. Even if this would work, I would certainly find another way to achieve this.

 

[Shane Kelly]

i've put them on a dimmer (variac ) before and that worked really well.
They were old fluorescents and it was about 15 years ago. Should be easy to test.

 

[Peter Mosiman]

I was on a shoot where the Gaffer/Best Boy achieved this effect by using a conventional tungsten dimmer. They are obviously not meant to work with fluorescents so as long as you just adjust the dimmer until the fluorescent starts to flicker. Depending on the bulb, you will get different amounts of flicker...at least that was my experience.

Good luck.

 

[Michael Romano]

The dimmer works pretty well but sometime you have either ON or OFF. If you don't a have a guy to man it, I've also achieved success with slightly disconnecting the tube in the fixture. The best ones even make ticking noises!

Mileage may vary and always remember to keep a fire extinguisher on hand when dealing with electricity

 

[John Brawley]

The director wants the fluorescent work lights to flicker on and off... how is this achieved ?

A flicker box ? I'm concerned that because fluorescent bulbs take a moment to strike that a flicker box might not work.

You need a gaffer with a collection of old tubes and old starters to swap into them. If the lamps are in the ceiling it's hard to put a dimmer inline.

jb

 

[Peter Reese]

Ask at the local Rental house - Normaly they stuck "old" Tubes or other that will make it flicker.. The god old On / Off is god - When you go shooting .. And all of a sudden the clint / Director. Wants the light on a fraction more... Because it went a bit to dark... You just give them that moment more - when dealing with special light solution.. Always have the plan so that it´s flexible so you can ad more or less...

Hope it works

 

[Michael Totten]

So I tried out a regular in line dimmer on some newer shop lights... at first it wasn't working... The lights would essentially just go off completely once the dimmer reached a certain point. Then after about 5 minutes (once the lights warmed up a bit) ... they did indeed flicker. It was unfortunately sort of a quick flicker.... where I'm looking for the longer flicker (something like half second intervals or so)... I'm thinking a mixture of dimmers and people working the on/off switch on other units will be the ticket.
Thanks for all the suggestions.

 

[Dan Hudgins]

Series

Series

If you don't have a variac you may be able to put a tungstan lamp in series with the FL fixture, that will drop the voltage, you can then turn the tunstan lamp on and off to make the FL dim somewhat. Normal dimmers have a SCR or TRIAC that can interact with the solid state ballast making the lamp turn off rather than dim much. A VARIAC is an analog device, as are inductive ballasts.

You can use two or more tungstan lamps and flip there switches in various ways to get more than one level of flicker brightness... You just wire them in parallel and use different wattage lamps in them.

Older FL fixtures used an inductive ballast and may work better than newer solid state ballast fixtures for filcker.

Another option would be to replace the FL lamp with cristmas lights and gel greenish in the fixture with frost gel to simulate FL lighting, then use a normal tungstan flicker unit on that.

 

[Michael Totten]

If you don't have a variac you may be able to put a tungstan lamp in series with the FL fixture, that will drop the voltage, you can then turn the tunstan lamp on and off to make the FL dim somewhat. Normal dimmers have a SCR or TRIAC that can interact with the solid state ballast making the lamp turn off rather than dim much. A VARIAC is an analog device, as are inductive ballasts.

You can use two or more tungstan lamps and flip there switches in various ways to get more than one level of flicker brightness... You just wire them in parallel and use different wattage lamps in them.

Older FL fixtures used an inductive ballast and may work better than newer solid state ballast fixtures for filcker.

Another option would be to replace the FL lamp with cristmas lights and gel greenish in the fixture with frost gel to simulate FL lighting, then use a normal tungstan flicker unit on that.

We will have a couple variacs on set.
So just to make sure I'm understanding you correctly, a variac works differently than the 300w Leviton in line dimmer that I used for the test?
I'm pretty sure that the FL lights at location are newer... so perhaps they won't behave in the same way... (or does the analog variac work with newer FL )?
thanks so much Dan

 

[Cail Young]

One gaffer I've worked with carried an assortment of dodgy fluoro ballasts for just this situation - swap out the ballast in the unit for a "known bad" one!

 

[Dan Hudgins]

Autotransformer vs. triac

Autotransformer vs. triac

We will have a couple variacs on set.
So just to make sure I'm understanding you correctly, a variac works differently than the 300w Leviton in line dimmer that I used for the test?
I'm pretty sure that the FL lights at location are newer... so perhaps they won't behave in the same way... (or does the analog variac work with newer FL )?
thanks so much Dan

Your Leviton probably uses a Triac which is a digital solid state switch that turns the power on and off at 120Hz (or 100Hz in 50cps places).

The dimming comes from the "duty cycle" that is it goes from close to 100% on time to about 30% on time then the light goes out all the way.

With a VARIAC you get about 135% to 0% in small steps but the output is a sine wave (more or less since there is a bit of distortion from the iron core) but the output of the solid state Triac or SCR dimmers is a sort of "square" wave with the on part that varies in width relative to the off part, so the voltage only varies during part of the AC sine wave, then falls to zero part of the time, when it falls to zero the mercury arc in the tube goes cold too long and the light locks off, until you turn the "duty cycle" up higher.

With the VARIAC and magnetic balast, the mecury gas (plasma) can become unstable at lower voltages, but since the voltage is not switched on and off (in a sine wave there is a small off but its almost zero time, with Triac is much longer off time), and "flicker" near its cut off point rather than go all the way dark.

Solid State balast work like the Triac dimmer, so when you feed a triac dimmer into a Solid State balast, they BOTH cut the voltage off 100% part of the time and the light turns off since the plamsa in the tube gets cold in the off part of the cycle. I read that you can convert mercury lights to DC with a full wave bridge, and then put a capasitor across it to hold the voltage for more than one AC cycle, that might solve the problem with the light going out on a Triac dimmer?

To start the plasma arc there is a "strike voltage" after which the lamp will glow until the voltage drops too low and then the arc goes out.

We have found that some FL fixtures seem to be able to be "boosted" about a half stop at about 135v, but it may blow others out. Most things may stand that since they are built for "surge" voltage on AC mains, it depends on how hot they get from being above 125v or their rated max.

=

I would go with putting small christmas lights and greenish and frost gel in the fixture since you can control that with more repeatable results, and use a power relay to flicker the voltage up and down from a "nail board" or computer program feeding out the filcker sequence on one of the parallel port pins.

That way when the director says "action" the flicker will repeat on cue for each take.

==

I think "quick start" FL tubes flicker when the "heater" at just ONE end is burned out, you may be able to use two VARIAC to burn out the heater at one end by overvoltage and see if that makes it flicker in a solid state balast (you do that with alagator clips not in a fixture). Another idea is to clip off ONE pin on ONE end of the tube that has four pins, that will still give an AC connection to both ends, but the heater in one end will not work as a starter. If the tube does not strike, try turning it up-side-down so the pins are reversed on the ends (rotate it on its axis 180 degrees but keep the ends in the same contacts).

 

[Dan Hudgins]

High Voltage

High Voltage

Another way to light FL tubes so they flicker is to use high voltage, that way they do not need the heaters and are instant on and off, which is sort of what happens with an inductive ballast since it will make High Voltage spikes when it has a break in its coil and is arcing.

I'm not sure what voltage to use, probably over 20,000v to maybe 150,000v but its a low current, and if high frequency AC is less likely to kill you, maybe.

I have seen FL tubes lit by Tesla coil before, its not as bright as normal, so you would need high ISO and fast lens to use them for primary expsoure.

If you wire direct to the tube pins and have an adjustable spark gap, you can make them flicker by adjusting the spark gap.

If you get an old sicence lab "induction coil" and a car battery, you can poke the vibrating contact to make the output vary and in that way make the FL tube flicker as the HV will also vary and the tube will respond right away since there is no balast or heater involved.

Its the same idea as when neon signs flicker, because there wire has come lose and there is a spark gap between the tube and the voltage source. In fact the HV transformers used for Neon tubes may work, but watch out as they put out more current than a small Tesla coil and its 60Hz AC not high frequency, so its "left hand in the pocket" rule and rubber shoes and gloves etc...