Cinematography Mailing List - CML

 

Search


Fluorescent Lights In Film &Video

Published : 3rd October 2004


I need some answers to working with fluorescent light in film and video. They are basic questions which I hope some people will help me either on or off the list. Here it goes. 60hz or 50hz what parts of the world fall into each section. How does a DP avoid flicker in either fluorescent light hz areas mainly having to do with the right shutter angle and film speed. I know lights like Kinos correct this problem but if you shoot for example digital video at 24p with regular fluorescent I should shoot at 1/60 instead of 1/50 shutter speed right?

Basically, I just want a primer on how to avoid the flicker or pulse that regular fluorescent light can create on film and video. Thanks in advance to my never ending classroom.

Brian Fass
Cinematographer
NYC



Good section in the American Cinematographer Manual: "AC Arc Lamp Flicker Problem".

And here on CML :

http://cinematography.net/edited-pages/FLORRIES.htm

http://cinematography.net/edited-pages/FluorescentLamps.htm

http://cinematography.net/edited-pages/SPEED.htm

http://cinematography.net/edited-pages/

SlowMotionUnder60hzFluorescent.htm

John Pytlak
Eastman Kodak Company
http://www.kodak.com/go/motion



Brian Fass wrote :

>Basically I just want a primer on how to avoid the flicker or pulse that >regular fluorescent light can create on film and video. Thanks in >advance to my never ending classroom.

Brian,

Think of it the same way you would consider the flicker of magnetic HMI's.

You need to shoot in the safe frame-rate, non-flicker, windows. In film that would be 24, 30, 40, 60 120 fps at 170 degree shutter for 60Hz countries. These numbers for both 50 and 60Hz countries are easily referenced in any of the good film manuals such as David Samuelson's or the ASC manual.

I'll let the experienced video shooters express their opinions on the best tricks to avoid flicker on video. I would imagine in progressive mode it is the same as film.

Most commercial and industrial spaces, especially older buildings, have magnetic ballasts in the fluoro lighting. Some fluoro's have high speed, flicker-free ballasts, the same as HMI's but it is not common. When in doubt, I check by popping off the cover of a light and checking the ballast itself. I stay in the safe windows when I can't determine the Hz of the lights. The frequency can also be checked by a freq meter using a photo cell to read the light source such as the B&S meter or a Fluke set up with

the photo cell. If this is the case, be sure to read the individual light as the light from another fixture can give one an errant reading.

Countries with 50Hz shoot 25fps as the base frame rate for synch sound. 60Hz countries use 24fps. The Hz of a country’s electrical power can be easily researched on the internet such as here :

http://kropla.com/electric2.htm

Most 120v are 60Hz and most 220v are 50Hz but there are exceptions (such as Jamaica) so be sure to check the list
before your travels.

I hope this helps a bit.

Best Regards,

Jim Sofranko
NY/DP



You can even hook up a silicon photocell to an audio amplifier and speaker/headphones, which allows you to "hear" any flicker in the light. With practice, you should be able to discern 50Hz from 60Hz. "Listen" to a lamp on an SCR dimmer -- even tungsten lamps buzz loudly with flicker as they are dimmed.

http://sofia.arc.nasa.gov/Edu/materials/activeAstronomy/section5.pdf

John Pytlak
Eastman Kodak Company



John Pytlak writes :

>You can even hook up a silicon photocell to an audio amplifier and >speaker/headphones, which allows you to "hear" any flicker in the light.

Yes…but in the context of CML, "flicker" usually means the end result of a mismatch between lighting output frequency and shutter speed. However, what you suggest may be used as a crude frequency meter that can easily distinguish between magnetic ballasts and electronic ballasts.

By the way, you won't hear 50 or 60Hz from magnetic ballasts unless your speakers or headphones are capable of reproducing such low frequencies!

And while all the magnetic ballasts in a given location are in sync (because their frequency is determined by the power line), electronic ballasts are free-running and not (as far as I know) crystal-controlled, so their collective output may be somewhat of a mix of frequencies...though still "flicker-free."

Dan Drasin
Producer/DP
Marin County, CA



>By the way, you won't hear 50 or 60Hz from magnetic ballasts unless >your speakers or headphones are capable of reproducing such low >frequencies!

What you typically hear is the first harmonic @ 100 or 120 Hz, and quite clearly sometimes...

Sam Wells



>By the way, you won't hear 50 or 60Hz from magnetic ballasts unless >your speakers or headphones are capable of reproducing such low >frequencies!

Actually, the light output waveform looks more like the following line but upside-down:

UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU

because even though AC current alternates direction once per cycle, the electrons excite the phosphors when they are running in either direction. Thus, though the full sine wave cycle repeats 60 times a second, the light output pattern repeats 120 times per second. I've been using a silicon cell on my "true RMS voltmeter with freq reading" as a light-checker for years.

Mark Weingartner
LA based



Yes, 100 or 120 cycles should be within the capabilities of a decent quality portable amplifier and headphones. It is subjective, but much less expensive than a frequency meter. Certainly any buzz can tell you if you have a potential flicker problem.

John Pytlak
Eastman Kodak Company



Brian Fass wrote :

>I know lights like Kinos correct this problem but if you shoot for example >digital video at 24p with regular fluorescent I should shoot at 1/60 >instead of 1/50 shutter speed right?

The main thing you can take away from this is that when shooting video you will see the results of power line freq,/shutterframe rate mis-match.

Earlier this year while in a school on an outlying island in the Marshall’s group, I was shooting 30 P 1/48 shutter, and had a strange color shift that would cycle through the frame every second and a half.

I switched to 1/60th shutter and that took care of it. The 30 P 1/48th frame rate/shutter combo was an accident by the way. doesn't matter in sunlight. Which is where I did most of my shooting.

Mark Smith
Oh Seven Films
143 Grand St
Jersey City, NJ 07302


Sponsored by

 

 

 

 

 

 

 

CML Home CML-Tests Home

© copyright CML - Cinematography Mailing List all rights reserved