The Basics of Rigging LED
If you have ever seen a video online of a stage collapsing or an LED wall wobbling back and forth…
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When LED screens are used in churches, live concert venues, and even corporate gatherings, there is a good chance that the LED screens will end up on camera somewhere. Livestreaming, multicasting, satellites, and IMAG (short for image magnification) have become incredibly popular over the last few years and rely on LED screens and cameras. Your LED screens and cameras have to play nice together.
As a refresher, each LED wall panel is made up of a number of components. We go into more detail on that HERE, but in short, each panel is made up of a 1) chassis or frame that supports the 2) LED modules which are controlled by the 3) receiving card and IC driver and powered by the 4) power supply.
A conversation about how an LED screen appears when it’s on camera starts at the IC driver.
WHAT IS THE IC DRIVER IN AN LED SCREEN?
The IC driver is what regulates the visual output of the LED screen. Very generally speaking, LEDs are either on, or off. With the right amount of voltage, the LED turns on. When the voltage falls below the threshold, the LED turns off. With early LED light bulbs, this was a big problem and there was no “dimmer”, it was on, or off.
As it turns out, that is still true. LEDs cannot dim. They are on or off, 1 or 0, true or false.
To achieve different brightness levels with LEDs, we have to trick the brain. While LEDs are very bad at dimming, they are very good at their on-ness and off-ness, and they can turn on and off really fast. So fast, in fact, the human eye can’t see that it shut off. Using a technology called Pulse Width Modulation, abbreviated PWM, we can control how often the LED shuts off and for how long to trick the eye into thinking the light is dimmer or brighter.
It works like this. An LED that is on 10% of the time will appear to be at a 10% intensity. We send one ON pulse and 9 OFF pulses in a span of time, let’s just say 100ms. The eye will not see the flickers, only the average of the time the LED is on, interpreting it as 10% brightness.
LED SCREENS ON LED SCREENS
If ALL the LEDs are going off and on at the same time, the eye might not be able to see it, but the CAMERA can. This is where you get artifacts like scan lines or pulsing on your LED screens when the LED Screen is showing itself or another screen. An interesting way to see this is to try looking at the LED screen with your phone camera in slow motion video mode.
Your church or venue might have TV cameras that can “see” the LED screens. Depending on the shutter speed of the camera and the refresh rate of the LED wall, you might notice problems.
To help combat this problem, THOR uses a technology called S-PWM (Scrambled Pulse Width Modulation). S-PWM effectively increases the refresh rate by chopping the video signal into smaller sections. The “Scrambled” part is that the signals are synchronized and offset in such a way that it reduces the time that all the channels are off. As a result, the negative effects on the camera are minimized.
Problems will still show up, there is no silver bullet here. There are a lot of factors that go into making LED screens show up well on camera. Using S-PWM is a HUGE step in the way of minimizing issues. The imaging chip and shutter speed on the camera will also make an impact.
If your venue or house of worship uses cameras, make sure you test out your cameras on the LED screens you are looking to purchase. Reach out our team if you have questions too. We’re always ready to help you get the right setup for your install.
