LED Flicker and Video

One of my activities more common activities during the Christmas season is designing lighting for my church using a variety of fixtures they have acquired overtime. While the majority of their LED product is of good quality they do have some off brand lights that flicker on video. This is a common problem with cheaper LEDs built with lower quality components. So here's and explination of why and a work around for recorded video only.

The video flicker comes from the way that the individual colored diodes are dimmed to color mix or for intensity. In order to dim an LED it is turned on and off rapidly maintaining its nominal operating voltage when in the on state. This helps preserve color integrity and relative brightness throughout the cycle no matter how long the LED is actually on. The process is known as pulse width modulation or PWM. For a look at this see the picture on the right. More often than not, this process happens more rapidly than the eye is able to perceive however sometimes camera's are able to pick this up due to their frame rate and shutter speeds. This process becomes more noticeable as the LED is "dimmed" (turned on less frequently in the waveform) such as when the fixture is at a low level or if certain colors are mixed. While the LED product may work well for live events without video there is no way to fix the problem when using video and the flicker is going to happen any time a camera is used. The best way around this is to buy "camera friendly" products that have a high PWM frequency or rely on other methods of dimming.

After doing some research I was able to find a solution that works decently for RECORDED video. I'm almost positive that this can not be employed on live video. Any ways here are the steps:

Open the video in an editing software that allows you to manipulate tracks (Final Cut, Adobe Primeier, Sony Vegas, etc.)

Copy the video track with the offending LEDs from the main track to a secondary one on top of the main

Delete the audio from the secondary track

Offset the secondary video by a frame or two

Set the opacity of the second track to ~50-60%

After messing around with the opacity and frame offset of the second track you end up with something masking the LED flicker. The video ends up turning out fairly decent but judge for yourself: