LED Walls Part 4 – What Drives LED Walls
Today we are going to touch on what drives the LEDs on the wall.
There are two major components in the LED Wall panel itself that you need to be concerned about. This would be both the IC driver for the LEDs themselves and also the receiving card.
The communication between your video input signal and each of the many LED panels is handled by both a “sending” and “receiving” card. Probably the most common system here in the USA is the Novastar brand. There is also Linsn and some other generic ones, but for discussion sake, I won’t go into them, as I cannot recommend that you pursue a LED Wall with a generic card.
The more important, but less obvious, thing is to pay attention to the IC driver of the LEDs. This is what regulates the visual output of what we see. Being that LEDs are able to flicker on and off very quickly, the way they vary in intensity is to use what’s called PWM – or Pulse Width Modulation.
PWM is essentially a digital on/off that by having the LED turned on for say 10% of the time and off 90% of the time at a very high speed, you see that as a lower intensity as compared to if it were turned on 100% of the time. So the issues that can pop up here is usually one of camera compatibility. I regularly use my iPhone camera on tests of projectors, lights, and other equipment and by using the slo-mo mode it picks up on flicker very well that can be seen in the playback. With TV cameras that your church may have – if the camera can “see” the LED wall, and depending on the shutter speed of the camera and the refresh rate of the LED wall that can cause problems – just like some of the low cost LED light fixtures show up on camera with flicker.
So one of the things to pay attention to is the refresh rate of the LED wall, and now there is a relatively new driver chip that will actually do a “Scrambled” pulse width modulation. This functions as an IC driver that will effectively increase the refresh rate much higher and instead of a typical scenario where if a refresh rate was very slow (for discussion sake here) at 1 second. If we wanted to have the red LED have an intensity of say 10%, then the red LED would turn on for 1/10 of a second, and then turn off for 9/10 of a second, only to then turn on for 1/10th again and then off for 9/10.
The S-PWM driver takes that scenario and chops up the 1/10th of a second into four 1/40th of a second chunks and then the “off” time between them is also cut by a factor of 4. So in this example, it’s quadrupling the refresh rate and hence minimizing the potential effects seen on camera.
I will say that the issues show up – but each camera and it’s respective imaging chip will have a lot to do with the overall system performance. (and I’m not going to turn this post into a camera discussion…)
So if you are looking at buying a LED wall – make sure you look into how it will perform if you plan to have cameras and if it will be within view of them.
One other thing that the IC driver has an effect on is the color and gray scale bit rate. I did include a sample image of a lower and higher bitrate so you can get an idea of why that is important.
*note – this is meant to be an overview and not an overly detailed whitepaper of the LED wall. I’m happy to answer more questions about this topic if you’d like…*
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