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LED Lighting at 24fps


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#1 Bill DiPietra

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Posted 20 September 2014 - 09:21 PM

I'm going to be doing a shot that has emergency lights reflected off of a house.  I've found a decent set of LED emergency lights, but I've never used LED lighting on film.  I believe the lights connect to the cigarette lighter socket of a car.  Can anyone tell me if I am likely to get any kind of weird flicker?

 

Thanks.


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#2 Stuart Brereton

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Posted 20 September 2014 - 09:35 PM

You shouldn't get mains flicker from a DC source, but I had a show a couple of years ago where we tried to use a LED Emergency beacon. It turned out that the flash of the beacon was of sufficiently short duration to cause rolling shutter artifacts. This may or may not be a problem for you.


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#3 Bill DiPietra

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Posted 20 September 2014 - 09:38 PM

You shouldn't get mains flicker from a DC source, but I had a show a couple of years ago where we tried to use a LED Emergency beacon. It turned out that the flash of the beacon was of sufficiently short duration to cause rolling shutter artifacts. This may or may not be a problem for you.

 

That's good to know.  Thanks, Stuart.  This one has different rates that it can be set to, from fast to slow.


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#4 Stuart Brereton

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Posted 20 September 2014 - 09:53 PM

So did ours. It's not the frequency of the flash that's the problem, it's the duration.


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#5 Bill DiPietra

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Posted 20 September 2014 - 09:58 PM

So did ours. It's not the frequency of the flash that's the problem, it's the duration.

 

I'm probably going to film a few shots with the lights reflected off the house and a few without for exactly that reason.


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#6 Mark Kenfield

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Posted 20 September 2014 - 10:33 PM

We used LED based police lights on a feature I shot last year. Was really worried about rolling shutter strobing issues - so we tested them in advance, turned out to be perfectly fine, and the effect worked a treat.


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#7 John E Clark

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Posted 21 September 2014 - 11:43 AM

Why 'leds' may give a pulsing 'light' effect, is due to how LEDs are handled electronically. Usually a short high voltage pulse is applied, since that yields a higher lumen value, than a 'steady state' voltage. Provided the duty cycle is such that the LED does not burnout.

 

However, this can produce problems in cameras that are scanning out regions of the sensor, depending.

 

I've never tested this out, relative to effect on Digital film... but I have noticed that if I see brake lights that when I avert my eyes, I see a sort of 'pulse stutter', rather than a smooth blur (what else are you going to do at a traffic light...), that the brake light is most likely pulsed LED.


Edited by John E Clark, 21 September 2014 - 11:43 AM.

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