Shooting Fluorescent Light Flicker

I will be shooting on location this weekend using uncorrected fluorescents as the only source. The bulbs are "34 EnergySaver Cool", manufacturer unknown. I'm assuming that this means Cool White, which I further assume to be a color temperature of about 4150K.

My questions is as follows :

- Are my assumptions valid? - What is the correct filtration on the camera to properly balance to tungsten stock? (I assume I'll need a MinusGreen and some fractional 85, but what fraction?) - What will be the effect of this filtration on the EI?

Thanks in advance for your help,

Chris "OK, so I'm still new at this" Freilich

Assume nothing with these things. I proposed the same question about 3 weeks ago to the CML and got fantastic results. (Thank you all!!!). The best advice I received was to use a color meter and not to guess. Cool whites vary in Kelvin and in green value depending on the brand.

This may not be good advice, but what I did was bought two cases of fluorescents and then returned them after I was finished shooting. This sounds cheep, but I was shooting a no-budget film. This way all of the flo's I was using where consistent with each other. (not to mention that older tubes also change color).

My stuff came out great! I hope you have as good luck as I did.

Christopher C. Pearson

There has been lots of advice about this already. But since you are still worried I will jump in:

1/. Don't 'assume' on the color temp. Rent or borrow a color meter and know for sure...be sure to measure on the color temp *and the magenta/green scale.* Used Color Meter IIs can be found cheaply sometimes as the 3 is out now. I bought a backup II for $200 last year.

2/. If the fluoro tubes are all the same you are cool. Take some of those tubes and put them into Molescent or other home-made fluoro fixtures as a key or fill source. You know they'll match even without a color meter!

3/. And/or, having established what the color output of the tubes is, make up a gel package for small HMIs (like 1200 Pars or maybe jokers) which will match. You can vary the color temp for an effect but make sure the magenta-green range matches. I predict +1/2 and +1/4 Plusgreen and 1/2 CTO will give you a close match--your HMI may vary! Gelling small tungsten lights up with blue and +green is an exercise in frustration. I don't remember if you said that your location has windows. Bear in mind that if you have uncorrected daylight against fluoros which you are correcting, the daylight will tend to go magenta. In video transfer this can usually be fixed but you may not have that option. Of course you can gel the windows or draw curtains, etc.

4/. I'd strongly suggest shooting 7246. Daylight balance puts you closer to the output of the fluoros than tungsten stock and '46 looks at least as good as '74 while being slightly faster.

5/. I have shot under fluorescents without a filter on the camera for years with great results. Why add glass and take away stop when you can correct it in transfer with much greater precision? In print your correction may leave some very slight evidence of the fluoro environment but that may not be a bad thing.

6/. As I have been there myself I will offer my unsolicited opinion that nothing is more typical of an inexperienced or insecure DP than being TOO CAREFUL. I don't mean you should be cavalier about what you're doing, but that you should not let worries about HOW to do something get in the way of thinking about WHAT you want to accomplish visually. It's important to realize that even in a case like this, rendering a perfectly balanced and neutral rendition of the situation is not the only way to go. Sure it's the most obvious thing to do---but do you always make the obvious choice? Technical knowledge is wonderful to have but I have known people who could quote the ASC manual from memory yet couldn't do an interesting shot or contribute an original idea to save their lives. Have you thought about what the scene might look like if it were green? Vittorio Storaro has done this in 'The Last Emperor' and 'One From the Heart'--and he's no slouch. Or, if it's a night scene, what if the fluoros were off except maybe a few 'emergency' tubes in selected areas (for these you could use Optima 32s or Warm White Deluxe) and you could use tungsten desk lamps for practicals and tungsten all the way? (Warm White Deluxe is a cheap, easily available tube which is about 3000K with only a tiny bit of green-- John Alcott used to use them.)

However you end up going, stay loose and have fun--you'll do fine!

On an upcoming film we intend to use fluorescents as part of the set design. To avoid the high cost of Kino tubes and ballasts, we're going to go for a commercially available tube with a high CRI, and a colour temp of either 5500 or 7500. We intend to fit these using off the shelf high frequency electronic ballasts (using a frequency of 120kHz) and my question is this: are we ok to shoot speed changes in shot, ie with 435, without danger of flicker? Are the commercially available ballasts OK, or are the Kino ballasts special in some way, eg squarewave rather than sinewave?

Again I intend to shoot a flicker test but would appreciate any comments.

Chris Plevin

Chris my recollection from the research i did a few years ago is that the significant difference between the ballasts that Kino uses and commercially available hight freq ballasts is that the Kinos overdrive the tubes, eg. pushing approx 900 milliamps through a four foot tube. This, incidentally will change the color spectrum output of the tube, notably adding a slightly stronger green spike from the more excited mercury vapour in the tube...but getting back to the issue, I do not believe that IN PRINCIPLE the flicker characteristics will differ between the commercial high freq ballasts and the Kinos. This is a guess based on recollections and conversations with ballast manufacturers...PLEASE TEST!!! ...and let us know what you found.

I would suggest a test with three cards in frame, one lit with a tungsten light, one with a kino, and one with a commercial electronic ballast. The tungsten - lit card will control for any anomolies caused by the camera. If you get test fixtures from Cirro-light in London, please give my regards to David Morphy. He may even lend a fixture for the test...(one can hope!) Mark

Also - in regard to the Kino ballasts - they cycle at 25,000 Hz - which makes them "flicker free" at any speed. I'm not sure that a 120 cycle will be safe for ramping - depending on what speed you choose. Since the gas will discharge at twice the frequency - 120 cycle will give you 240 "flickers" per second. The rule of thumb seems to be a "shutter speed" of not less than your Hz cycle - so as long as you stay at 1/120 of a second or faster you *should* be fine. -- Also keep in mind the decay time for the phosphors against the tube might make things dangerous at anything other than 180 degree shutter. This would mean that you really couldn't go any faster than 60fps at 180... but again - as is preached over and over - test, my good man, test.

Jay Holben

http://users.aol.com/adakinprod

My experience with the commercial ballasts is that you can shoot any speed without flicker. I've shot many different non-window fps with no flicker. However, I've never ramped with them but I would think you could do it. Of course, do a test with them. I have heard that the potential for flicker exists with the commercial ballasts when they are dimmed. Best of luck and I hope this is helpful.

Regards,

Jim Sofranko

Jay, I think you misread the posting, the ballast I checked out runs at 120,000 Hz. Should be flicker free at that speed. But I will test - Mark described exactly what I had in mind - and report back.

The Kino tubes have a high CRI, about 95, and of course everything offered up as 'film equipment' is more expensive; the ballasts are nicely packaged and are dimmable, and the lighting fixtures are well thought out. That's what you pay for, I guess.

On an associated note, I saw some fixtures at the TV show in London by a company called Videssence, which were very bright for small size and power. They had some deep egg crate accessories which made the soft light much more directional at the cost of a stop or so, but the tubes they used were of looped construction, like a U shape, and thinner than Kino tubes. Samuelson Lighting in London have some, although not on the hire list yet, and they look well worth checking out, particularly for location lighting.

Chris Plevin

There's also a German company - High Lux that makes the same thing - although not quite perfected. They go by the principal that a fluorescent is only as bright as it's surface area - so a 2' "U" shaped lamp has the same brightness as a 4' tube in half the space. Add a second "U" to that and you have the output of an 8' tube in a 2' space... They get some great output from the fixtures, but they still haven't quite gotten the spectrum right. Ah well... Back to the drawing board...

Jay Holben

http://users.aol.com/adakinprod

Regarding output, surrface area is only part of the equation...current is another part, and one reason for using larger diam. tubes is to stop the mercury in the tube from getting too hot which reduces efficency and shifts color temp. Most of the compact fluorescent lamps out there are not really good CRI yet...and boosting them (overdriving them) only exacerbates the color problems. There is a rumor about of an upcoming very high CRI compact fluorescent lamp made under exclusive contract to a company that provides fluoro stuff to our industry...more to follow.

Mark