Clay's Corner | Direct View LED Video Walls Part 1 of 4
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Clays Corner Direct-View LED Video Walls Article 1 Headline
Direct-View LED Video Walls
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Pixel-pitch is the distance between the center of one RGB LED to the center of the next RGB LED in any direction. This is probably the single most important consideration when selecting products for a Direct-View LED video wall. This is because the distance between the LEDs determines the apparent resolution of the image.
Pixel-pitch in Direct-View LED video wall is akin to resolution in an LCD display.
I’ll use an analogy using televisions. Today, everyone seems obsessed with buying 4K UHD televisions. The same thing happened several years ago with 1080p FHD displays. It makes me laugh because in many cases it’s just a waste of money. Resolution is a perceived density of the image. In other words, up close, you can see space between the dots that make up the image, while at a distance, you cannot see any dots at all.
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If you’re buying a small 19” television for your kitchen as an example, and the minimum viewing distance is likely 10 feet away, a 720p HD television is all you need. This is because such a small image at a fair distance away yields a perceived image with no space between dots. Alternately, if you are using large computer monitors sitting right in front of your face, you need a very high-resolution 4K display so you don’t see the dots up close. The moral of that story is that you don’t need to waste your money on 4K when you’re viewing from farther away or when the display is small. You DO need highest resolutions when your viewing up close and with a larger display.
How does this analogy affect the way we chose Direct-View LED video walls?
The same perceived image criteria is present in the human brain regardless of the medium used for viewing. However, Direct-View LED technology is such that we can only get the dots as close together as the size of the individual LEDs will allow. Right now, surface-mounted LED manufacturing only allows for spacing of just under 0.9mm. You and I both know that will get smaller in time. But for now, we have to have enough space for the LEDs to be soldered to the circuit board, and the little solder tabs on the SMA LED devices has to be about that far apart.
We need to consider minimum viewing distance and overall display size to understand how the space between the dots affects our perception of image quality. There is also a time element involved, in that if you’re only viewing for a short time the mind does not perceive the missing image content because it’s busy digesting the available image content. This is exactly why outdoor LED signs have such wide pixel-pitches. First, you’re viewing from far away. Then, you’re only looking at it for a few seconds as you drive by in your car.
Now, let's consider Direct-View LED video walls. Ask the question, “what is the minimum viewing distance?” Take into consideration the anticipated size of the video wall here. This is because you can’t say that someone might look at the video wall from a foot away when the display is twenty feet wide. That would be ridiculous because you’d have to be more than ten feet away to see the entire display. So, be practical. Plan the overall display size to fit the space as you always would. Then, place the closest viewing distance far enough away that you can see the entire display. Make a note with that closest, or minimum viewing distance in feet.
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How minimum viewing distance determines maximum allowable pixel-pitch.
Everybody’s enamored with 0.9mm pixel-pitch displays. They see them at a show and have to have one. Yes, they are cool and yes, they look just about as good as a television. Right now, they’re terribly expensive. Can the end-user really afford that? Do they even want to spend that kind of money? If the answer lends to a more conservative decision, I will show you how to establish a minimum budget to accomplish your task.
First, we have to use standard procedure to establish an overall display size requirement. This is no different than what you would use to determine a projection screen size or an LCD video display size. As an Avixa certified CTS-D, I use their tools to assist me in calculations. Their new tool is called DISCAS. It can be found here. (https://www.avixa.org/standards/discas-calculators)
The first order of business is to determine the level of viewing. Are they looking at detailed content such as spreadsheets, engineering drawings, or highly detailed documents? Or, are they just looking at pictures or videos? From this, you can use DISCAS to determine the size of the display based on the required size of the text, numbers or other content. Part of this is knowing that the content has to be legible to the farthest viewer.
Once you’ve established your display size, you can use a simple calculation to determine the maximum pixel-pitch that you should recommend.
First, a little disclaimer. I’ve done a lot of research and have discussed my findings with a number of Direct-View LED manufacturers. I have determined that by using a multiplier of 3.2 we can confidently recommend the proper pixel-pitch that both allows for visual detail and a comfortable viewing experience. I have read papers from various manufacturers that use multiplier of 3, 5, and even 8. Higher is better. However, the determining factor will always be ROI (return on investment). Where does the sweet spot lie where the image is good, and the price is right? So, I will use a multiplier value of 3.2. Chose you own if you’d like.
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Here's the calculation:
Minimum Viewing Distance = Pixel-Pitch x Multiplier
Pixel-Pitch = Minimum Viewing Distance / Multiplier
Let’s assume that you now know the closest viewer location and have been practical in making that determination based on the anticipated display size. We can use the formula above and our multiplier, (I will use my 3.2) to determine the widest pixel-pitch that I can confidently get away with recommending.
Minimum Viewing Distance = 20 feet
Pixel-Pitch = 10 / 3.2
20 / 3.2 = 6.25mm pixel pitch
Here’s another example:
Minimum Viewing Distance = 10 feet
Pixel-Pitch = 10 / 3.2
10 / 3.2 = 3.125mm pixel pitch
And, one more useful example:
Minimum Viewing Distance = 5 feet
Pixel-Pitch = 5 / 3.2
5 / 3.2 = 1.5625mm pixel pitch
You can see that even at 5 feet we don’t NEED to spend big bucks on the 0.9mm Direct-View LED video wall. That being said, always round DOWN. A smaller pixel-pitch is always better until it costs too much for the end-user. In the case of the 5-foot minimum viewing distance, I would choose to recommend the 1.56mm Neoti UHD Direct-View LED video wall. If budget allows, I would kick it down one notch and offer the 1.25mm Neoti UHD Direct-View LED video wall as an alternate.
What I’ve done here is, I’ve established a minimum budget number for the end-user. If they want Direct-View LED, they cannot spend less than the cost of the 1.56mm product in that application. I can just about guarantee that anything less would be hugely disappointing. I have also shown that if they can spend a little bit more for the 1.25mm product, they’ll be even happier. This is especially true with high-detail content. As a habit, I always move down one notch in pixel-pitch for highly-detailed content applications.
This is your worst-case budget-establishing technique. Of course, you should recommend the finest pixel-pitch that is both affordable and practical. (remember, no 4K UHD 19” televisions in the kitchen!) I think you will find that very successful projects come out of delivering good quality at an affordable cost. Choosing the proper pixel-pitch for Direct-View LED video walls is the most important building block.