LED stage lighting flickers in video

johnmeyer wrote on 12/11/2008, 6:15 PM

The reverse phase control looks similar to the CA3059 zero voltage switch from RCA that I've used for the past twenty-five years. It ensures that the turn-on happens only at the zero crossing, and therefore eliminates inductive transients when driving traditional incandescent bulbs or inductive loads like motors. You can create circuits which keep the power applied for the entire 1/120 second of a cycle, so there is no switch off transient either. You then alter the power applied by only turning on every other cycle, or every third cycle, etc. Works well, but you don't get very fine control, and it certainly would not be appropriate for dimming.

For LEDs, where inductive transients are not an issue, I don't know whether the this reverse phase circuit would be useful or not.

farss wrote on 12/12/2008, 12:05 AM

In the interests of trying to understand the problem today I tried shooting some footage of the el cheapo LED light I mentioned above with my EX1. This light runs off the 240V 50Hz mains. It uses a full wave bridge rectifier after two capacitors to produce a DC voltage that powers 225 white LEDs is some series / parrallel arrangement. I haven't been game enough to put a meter or a CRO onto anything live in this light. There does seem to be a small capacitor on the output of the rectifier followed by a ~1W resistor in series with the connection to the LEDs.

I tried both 24p and 25p at 1/50th shutter speed and I could not see any flicker. I made a point of having the EX1's flicker filter off. Tomorrow time permitting I'll try increasing the shutter speed.
I'd really like to get to the bottom of the problem earthriser has had.
If certain cameras have issues with certain kinds of LED lighting it'd be good to find out the why and what before this kind of lighting becomes any more popular.

Bob.

fausseplanete wrote on 12/12/2008, 7:39 PM

LED Genlock soon?

earthrisers wrote on 12/13/2008, 10:14 AM

Local update: Last night we attended a rehearsal (of one of the many local "Nutcracker" performances in our town [Santa Barbara]), and set up a couple of cameras to watch for LED flickering.
One of the cameras is a JVC HD (don't know which model number... but its cost was about $6K), which is the camera that had the "flicker" problem at the other theater last week. The other camera is a Sony PD170.
Neither showed any flickering last night.
We weren't able to talk with the tech crew at the theater, so we don't know for sure if they even WERE using LED lighting (the techguy at "last week's" theater told us that last night's theater had gone all-LED).
So it's possible that they were not using LED, or that they were using LED but have a more sophisticated control system than the first theater. Gotta find that out...
In any case, we're ready for tonight's shoot at the second theater, feeling pretty confident about not having flicker for this particular show.
But the question/investigation remains open...

tim-gennert wrote on 6/17/2018, 10:08 AM

I was presented with very important video that had severe flicker due to LED stage lighting. The flicker only happened where the light fell on the stage and performers. the video was shot 60I because it was going to DVD in the end. I was able to fix this successfully by using two plugins together in After Effects, although it may work in Vegas as well. First I used Re:vision fieldskit V3 with frame blending. http://revisionfx.com/products/fieldskit/after-effects/. Then, next in the chain I used Digital Anarchy's Flickerfree with the Rolling band preset for LED lighting. https://digitalanarchy.com/Flicker/main.html. I rendered the video using this codec (H.264 1080p HD). this changed the quality very little. The downside is that even on a fast system render time was long. about 13:1. Of course this is was not important because the video could not be reshot and this solution took care of it.😀