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Fluorescent Flicker


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#1 Charles Haine

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Posted 23 October 2005 - 10:58 PM

normally, when shooting at 24fps, i don't worry about fluorsecnts flickering in shot. The only time I've ever had a floro flicker on me was when I shot with a Arri S with a governor motor, and the unit was in frame and I noticed the unit flicker, but the light it cast was so diffuse that flicker was unnoticable.

I was gaffing for a DP I don't normally work with last weekend, and we matched the floro's, and I mentioned something about whether or not he was worried about flicker, and he said he wasn't because the building was too old to be set up with the newer, power-saving frequency.

Now, we were shooting pretty fast, and I'd already had to ask him a few things, so I didn't feel like having him take the time to clarify, but what was he talking about?

Do fluorsecents really never flicker except for energy saving electical systems? Any ideas what this guy meant?

thanks,
chuck
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#2 Johnny Derango

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Posted 24 October 2005 - 02:39 AM

normally, when shooting at 24fps, i don't worry about fluorsecnts flickering in shot. The only time I've ever had a floro flicker on me was when I shot with a Arri S with a governor motor, and the unit was in frame and I noticed the unit flicker, but the light it cast was so diffuse that flicker was unnoticable.

I was gaffing for a DP I don't normally work with last weekend, and we matched the floro's, and I mentioned something about whether or not he was worried about flicker, and he said he wasn't because the building was too old to be set up with the newer, power-saving frequency.

Now, we were shooting pretty fast, and I'd already had to ask him a few things, so I didn't feel like having him take the time to clarify, but what was he talking about?

Do fluorsecents really never flicker except for energy saving electical systems? Any ideas what this guy meant?

thanks,
chuck


I really hope you get some intelligent replies here. To my knowledge, it is only older ballasts that you have to worry about. I'm about to do a shoot in a grocery store and I had the same question. I know florescents have a broken spectrum so flicker is a concern, I just don't know when you should be worried. The few times I have shot under florescents, I just filtered in camera with a CC30 magenta and everything looked great, but I'm wondering if I've just been lucky so far.
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#3 Phil Rhodes

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Posted 24 October 2005 - 04:36 AM

Hi,

Energy-saving lights are not necessarily a flicker problem. Certainly, any fluorescent that's battery powered is almost certain to be high-frequency, and many of the light-bulb-replacement style units have the ringing-choke drive arrangement that provides very high frequency output.

Phil
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#4 oscar jimenez

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Posted 24 October 2005 - 08:14 AM

Hi, were u shooting at 24 fps? I have only noticed flicker with fluoros at speeds higher than 48 fps, and that is for old ballasts issues. goodl luck
Oscar




Hi,

Energy-saving lights are not necessarily a flicker problem. Certainly, any fluorescent that's battery powered is almost certain to be high-frequency, and many of the light-bulb-replacement style units have the ringing-choke drive arrangement that provides very high frequency output.

Phil


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#5 Sol Train Saihati

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Posted 24 October 2005 - 10:45 AM

Shot a club scene at 150fps the other day and one of the kinos was flickering like damn strobe. Turned out the effect wasn't all that unpleasant, but in the future I will ensure we have have ballasts in a decent state (if that is the cause)? I foolishly thought "flicker free" meant flicker free.
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#6 Michael Nash

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Posted 24 October 2005 - 05:01 PM

I know florescents have a broken spectrum so flicker is a concern, I just don't know when you should be worried. The few times I have shot under florescents, I just filtered in camera with a CC30 magenta and everything looked great, but I'm wondering if I've just been lucky so far.


The color spectrum of fluorescents and the flicker or pulsing of the output really have nothing to do with each other. Flicker is caused by capturing irregular peaks and dips of the lamp's output cycle (when the camera and light cycle are out of synch with each other), and the color spectrum of the light just is what it is, so to speak.

On rare occasions I've seen a pulsing color shift from HMI's when using a video camera's clear scan, but I've never encountered any inconsistent color shifting from fluorescents. It's usually the exposure pulsing that catches your eye first.

Shot a club scene at 150fps the other day and one of the kinos was flickering like damn strobe. Turned out the effect wasn't all that unpleasant, but in the future I will ensure we have have ballasts in a decent state (if that is the cause)? I foolishly thought "flicker free" meant flicker free.


Kinos ballasts are supposed to have a fast enough cycle that flicker is generally not a problem, but there is still a cycle. I forget the exact number for kinos, but when you get into faster frame rates you need to pay more attention to the math.

150 fps is "off" from the cycle of commercial fluorescents (not necessarily the kino's though); 120 fps would be mathematically safe for 60hz power but still no guarantee. At that rate you're excatly matching the cycle of the fluorescents, so it is advised to phase your camera to the lights to ensure you capture a peak, and not a dip, of the output.
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#7 Johnny Derango

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Posted 24 October 2005 - 06:30 PM

The color spectrum of fluorescents and the flicker or pulsing of the output really have nothing to do with each other. Flicker is caused by capturing irregular peaks and dips of the lamp's output cycle (when the camera and light cycle are out of synch with each other), and the color spectrum of the light just is what it is, so to speak.

On rare occasions I've seen a pulsing color shift from HMI's when using a video camera's clear scan, but I've never encountered any inconsistent color shifting from fluorescents. It's usually the exposure pulsing that catches your eye first.
Kinos ballasts are supposed to have a fast enough cycle that flicker is generally not a problem, but there is still a cycle. I forget the exact number for kinos, but when you get into faster frame rates you need to pay more attention to the math.


Unfortunatly, I had a major problem with color shifting in a room of florescents. I was shooting a TV pilot in an interrogation room lit maily by the overhead florescents. When we later went back and watched the footage, which was shot on 3 DVX 100-A's we noticed that the footage cycled from warm to cool and back again.... And when I say this I mean it went from nice warm flesh tones to a cooler white to blue to green and back. I had never heard of this before and there was no flicker. We were shooting at 1/48th shutter in 24pA mode. So needless to say Florescents scare me.

I realize that the color tmeperature has nothing to do with the flicker, so to clarify my question, when do you need to worry about florescents and flicker when shooting at 24 frames a second on film?

Edited by jderango, 24 October 2005 - 06:32 PM.

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#8 Glenn Hanns

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Posted 24 October 2005 - 08:16 PM

Unfortunatly, I had a major problem with color shifting in a room of florescents. I was shooting a TV pilot in an interrogation room lit maily by the overhead florescents. When we later went back and watched the footage, which was shot on 3 DVX 100-A's we noticed that the footage cycled from warm to cool and back again.... And when I say this I mean it went from nice warm flesh tones to a cooler white to blue to green and back. I had never heard of this before and there was no flicker. We were shooting at 1/48th shutter in 24pA mode. So needless to say Florescents scare me.

I realize that the color tmeperature has nothing to do with the flicker, so to clarify my question, when do you need to worry about florescents and flicker when shooting at 24 frames a second on film?



I have had a similar colour shift on the DVX100, It came down to the auto white function, if you shoot under flouros with auto on, the camera has a problem with the discontinuous spectrum and hunts for correction. Try shooting with a manual setting next time.
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#9 Michael Collier

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Posted 24 October 2005 - 08:38 PM

Yeah, basicly any camera (video, CCD, not sure about CMOS) will have that problem in auto white. Even the betas I have at work do that. I once got a call from the reporter/photog in fairbanks (Alaska) saying here veiwfinder was going bright then dark. when we got the clip emailed to us we saw exactly what you are describbing.

I figure that at different points in the floros cycle one color takes dominance, sort of how when you dim a light with a dimmer it becomes warmer. if the camera is in close sync with the floros (29.97fps, almost 2times 60fps) it will hit on the same point in the cycle up for several frames in a row. but as they fall out of sync it will expose more during its cooler phase and then go back to the warm phase. Think of two cars with their blinkers on. each blinker is almost the same rate. but if they do line up, they will probably fall out of sync for a while, become alternating and then go back to sync.

This also applies when you have your shutter on, or in film camera I would immagine putting a 270degree shutter would give the same effect. Bottom line watch out for floros. guys ready to shoot HD or 4K movies and drop film (im sure I have enraged many film lovers, but face it, its going to be gone once the D-20 and dalsa make a name for themselves) will enjoy being able to at least see if they have the rate off just a little and compensate, or replace the floro with a tungsten.

ps I know there is no real 4K workflow yet. there will be. soon electronic sensors will rival film in exposure lattitude, frame rates availible, color space, and vurtually every aspect of the picture. the film 'look' I think is purely experience based. you have seen movies that have touched you and the film grain and look has been directly linked in your brain to a sense of surealism. I'm sure that in time people will associate the film look the same way people think of old darreauge proccess photos (not sure on the spelling, but 1800s pictures exposed and printed on sensitized copper.) outdated and flawed.
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#10 Dimitrios Koukas

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Posted 25 October 2005 - 02:39 AM

Unfortunatly, I had a major problem with color shifting in a room of florescents. I was shooting a TV pilot in an interrogation room lit maily by the overhead florescents. When we later went back and watched the footage, which was shot on 3 DVX 100-A's we noticed that the footage cycled from warm to cool and back again.... And when I say this I mean it went from nice warm flesh tones to a cooler white to blue to green and back. I had never heard of this before and there was no flicker. We were shooting at 1/48th shutter in 24pA mode. So needless to say Florescents scare me.

I realize that the color tmeperature has nothing to do with the flicker, so to clarify my question, when do you need to worry about florescents and flicker when shooting at 24 frames a second on film?


If you are in a voltage system that works at 60HZ period and you have an 180 degrees shuter then no worries at all at 24fps.
But if you want to be absolutely sure, there are some equipment that u just point to the light and click and you get their rate.
Dimitrios Koukas
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#11 Michael Nash

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Posted 25 October 2005 - 05:32 PM

I realize that the color tmeperature has nothing to do with the flicker, so to clarify my question, when do you need to worry about florescents and flicker when shooting at 24 frames a second on film?


The rule is that 24 fps is a "safe" speed at any shutter angle when using 60hz. lighting. So I guess the issue is knowing if the ballasts in commercial lights are functioning properly and puting out a true 60hz. cycle. But the beauty of video is WYSIWYG -- when shooting under practical fluorescents, just monitor carefully. But with cameras like the DVX, there's not a whole lot of adjustment you do in camera to fix it.
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#12 Johnny Derango

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Posted 26 October 2005 - 05:13 PM

I have had a similar colour shift on the DVX100, It came down to the auto white function, if you shoot under flouros with auto on, the camera has a problem with the discontinuous spectrum and hunts for correction. Try shooting with a manual setting next time.


Glen,

The interesting part of the story is the auto white function was not on. all three cameras were set to shoot at pre-set 3200K. HAs anyone ever had this problem while in a pre-set? Please let me know.
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