Longtime industry expert Alan Brawn predicts the future of digital signage using lessons from its history. Projectors have innate and unique advantages, he argues, and they are here to stay, despite impressive advances in newer display technologies like MicroLED which are still in development but are poised to become massive forces in the industry.
May 28, 2024 | by Alan Brawn — principal, Brawn Consulting Raspberry Pi Led Matrix
For those of us who are practitioners of the business, art, craft, and (in some cases) the science of digital signage, there is usually a favorite element that engages us. For some, it may be content creation. For others, it may be marketing and analytics — with content management thrown in for good measure.
For me, the passion is (and always has been) displays — even before digital signage became a "thing". It will come as no surprise to those familiar with my work that I will begin our tale about displays with an abbreviated version of the evolution of displays, for context in how we got to where we are today. At the end of this trip down display memory lane, I promise to address the newest of the new displays we use in digital signage. These include MiniLED, MicroLED, and full color E Ink displays.
Buckle up — the ride will be a little long, but I promise it will be smooth!
"Displays" go all the way back to the prehistoric era, and the pictographs they painted on cave walls. It was not about painting for the sake of art but rather to visually inform (and in most cases warn of nearby dangers) in a more pervasive and permanent manner than the spoken word or something etched with a stick in the sand.
This is how it all began — but it is appropriate to apply what Jean-Baptiste Alphonse Karr, a French critic, journalist, and novelist, wrote in 1849: "The more things change, the more they stay the same." In an overriding sense, this is true of displays as well. Modern displays are still used to visually inform in a pervasive manner, but they have the added options of mobility, interactivity, and entertainment.
Under the umbrella of electronic displays, we have evolved from analog to digital. My experience spans the golden age of film to the era of the cathode ray tube (TV sets and then projectors) and all the way to DLP, LCoS, and LCD projectors — and, on the flat panel side, plasma, LCD, OLED, and dvLED digital displays. In the early 1950s my family's first TV was an 8-inch round tube CRT television set, and today I have a 75" LCD flat panel 4K display in my bedroom. As an iconic TV ad was famous for saying, "We have come a long way baby!"
With all the hype about flat panel displays, there are those that think projectors are a thing of the past. Yes, they were historically significant, but they remain relevant today. Pound for pound, they still produce the most cost-effective large screen images in the wonderful world of displays. To be fair, there are mitigating issues to be considered like ambient light, screen types, and installation factors, but they can do some things flat panels cannot. For example, projectors offer compact size and portability, edge blending, curved screens, and pixel mapping, to name a few. Depending on what research you believe, projectors still account for 10% of the digital signage display market. I can hear the heated discussions beginning on this topic already, but now, on to flat panels!
Traditional flat panels (not projection cubes) feature one of two image creation processes:
It is fair to say that LCD flat panel displays reside at the top of the food chain of display solutions for most digital signage applications. From 2-inch panels, all the way up to 120-inch diagonal sizes, LCD had ruled the proverbial display roost for years — and no matter what you may hear, they will continue to reign supreme for the foreseeable future. LCD is a mature technology that has benefited from years of product development and manufacturing efficiency with the costs (especially for larger sizes) declining for some time. It offers high resolution — up to 8K, with 1080P and 4K dominating. High brightness models are available in the 3K-to-5K nit range, and some models can operate reliably for a 24/7/365 duty cycle and give 60,000 hours of service. Finally, they LCD displays can be "matrixed" beside or on top of one another to create videowalls of nearly any size and configuration imaginable.
For videowall applications, the Achilles heel of LCD flat panels resides in the fact that there are visible seams between displays. Models with thin bezels go a long way to address the visible seam issues, but seams remain as a distraction. Another potential issue is that LCD can exhibit image retention (a.k.a. "burn-in," like the old plasma displays). This happens when a high contrast image is left on screen in a static mode for extended lengths of time and the "ghost" of that image remains. These issues have not dramatically hindered LCD use in the majority of commercial and digital signage applications, but it has opened the door for direct view LED to take some of the limelight.
Some consider direct view LED a new kid on the block, and relatively speaking it is. But the core technology and new applications in displays can be filed under "what is old is new again." The first LED for industrial use as a point light source was put on the market in 1962. It was bright red, but by 1971 green, orange, and yellow lights made their debut. With the introduction of blue LEDs in the 1990s, it became possible to produce white by selectively combining the proper combination of red, green, and blue light. By the late 1990s full color RGB LED displays were possible.
Applications for full-color (a.k.a. RGB) LED displays began with outdoor signs in places like New York, Las Vegas, and Tokyo plus large sports stadiums around the world. The signs could withstand the elements, especially the high ambient sunlight. In those days the displays were literally hand-built. Individual LEDs were installed on a circuit board. The distance between individual LEDs (pixel or dot pitch) was large — in the 16mm-to-40mm range. This was acceptable because the people that were intended to view the signs were at a distance (sometimes half a mile away) where the individual pixels were not visible at that distance. But as you got closer to the signs the pixels began to stand out. Thus, what some called "course or large dot pitch" LED displays were mostly relegated to outdoor applications.
As LED technology began to mature and improve, the ability to manufacture finer dot pitch displays came onto the scene. The industry quickly developed 8mm-to-10 mm outdoor displays — and, following that, down to 4mm. Today there are a few companies that even have 2mm outdoor displays for true close viewing applications. This evolutionary process allowed LED displays to be used in a larger variety of outdoor applications and increasingly indoors at closer viewing distances.
Let me take a moment and explain the basic issues of viewing distances and pixel pitch. One of the major goals (along with brightness, colorimetry, and contrast) of any large screen digital display is to avoid seeing discrete pixels. Projectors and, specifically, LCD flat panels accomplish this by using high resolution (1080P, 4K, and 8K) imagers/chips. On the LED side the original long viewing distances were such that high resolution via what we now know as fine pitch LED was not required. Fast forward with the demand for indoor applications and closer viewing distances, and if the goal is to avoid seeing pixels (and it is), the smaller pixel (or dot) pitch becomes paramount. This just proves that necessity remains the mother of invention. The continuing development of fine, finer, and — most recently — the finest dot pitch LED displays (more on that in a minute) permitted closer viewing without seeing those pesky discrete pixels.
As a rule of thumb, you can use the 10X rule of pixel pitch and viewing distance. A viewer with 20/20 vision (visual acuity) will not typically see pixels on a 2mm display at 20 feet. Get closer and pixels will be seen. As pixel pitch gets smaller, the prices significantly increase, so this necessitates "matching" the viewing distance with the applicable pixel pitch. For example, if the typical viewing distance is 20 feet, it does not make economic or visual acuity sense to use a 1mm dot pitch display.
The big break in the expansion and acceptance of LED displays came from advances in R&D and manufacturing. Driven by the demand for indoor applications and closer viewing distances this resulted in the wave of sub-3mm pixel pitch displays. In seemingly no time at all, 2mm became the (temporary) sweet spot for indoor displays. If you consider typical viewing distances of large screen images over 100-inches diagonal (currently averaging over 20 feet away), this makes sense. But the march toward and demand for even finer dot pitches was pushed along by 4K flat panels that were commonly available in up to 100-inch diagonal sizes and projectors that could do native 4K. LCD flat panels and LED are different in many significant ways, but image-wise they tend to be compared — and LED had to compete in its own unique way. As this is written, the new (temporary) sweet spot for direct view LED displays is 1.5mm and quickly heading toward 1mm.
But there is more to this story…
Now we dive headlong into "new(ish)" territory for LED. This is the sub-1mm category. Go back to the goal of not seeing pixels and the 10X rule — most of us can't see pixels on a 1mm display at 10 feet. I was at a trade event recently and saw a 220-inch diagonal 1.5mm LED display, and from less than 20 feet away it looked spectacular. This all raises the question of just how small a pixel or dot pitch needs to be.
There is a subjective part of the answer but do the objective math. To see pixels in a 0.7mm or a 0.5mm display, you must be less than 5 feet from the screen. Just how close do you typically view that 100-inch-to-240-inch screen? I remember in the early days of digital displays (projectors in this case), and viewers who were used to analog CRT projectors (no discrete pixels but lines of resolution) would go right up to the screen and exclaim, "I can see those pixels!" When tasked with going back a few feet to normal viewing positions, the pixels miraculously disappeared — what a shock! We end up with cost as the mitigating factor. It boils down to how fine a pixel pitch you need relative to visual acuity and how much you are willing to pay at whatever your typical viewing distance is.
As promised, we now find ourselves at sub-0.5mm dot pitch LED displays. This falls under the MicroLED category. Before moving forward though, I want to provide a short (intentionally non-technical) explanation of LED names/types you may run across.
Current MicroLED sizes are as small as 50 micrometers (about 0.002 inches) across, making them 1/100th the size of a conventional LED. That's almost small enough to serve as a single pixel in a conventional 4K LCD flat panel display. This is where MicroLED gets interesting.
MiniLEDs provide a refinement on the existing LCD backlight and entry into smaller pixel pitch direct view LED, while MicroLED promises to be more revolutionary, offering a technology that can go head-to-head with OLED and other advanced flat panel displays and win, with seamless images, better brightness, higher contrast, and more vivid color not to mention nearly limitless sizes and configurations.
Cutting to the chase on displays that we will continue to use for commercial AV and digital signage applications, here is where we are at.
Projectors will remain with us. As noted before, they provide the most cost-effective large screen displays (above 100-inches diagonal), even with the screen taken into consideration. Some models are large and can produce up to 50K lumens; but many models are small (three-to-six pounds), supplying 6K to 8K lumens of brightness and significant portability along with capacity for use in fixed installations. Projectors can offer high resolution with high brightness images that incorporate solid state illumination for long "lamp" life (20K hours). They have excellent colorimetry and screen size can be variable or custom-tailored to an application. Depending on the model, they can provide seamless edge blending and creative pixel mapping capabilities.
LCD flat panels are (and will remain) at the heart/head of digital signage. The technology is mature, robust, and cost-effective.
They come in sizes ranging from less than 2-inches all the way up to approximately 100-inches-to-120-inches. Some "raw" panels can even be "stitched" together to become even bigger, but this is rare and expensive. They can support a variety of aspect ratios, though they typically come in 16x9. Resolutions are available from under 1080P (full HD) to 4k (most common) and even 8K. LCD comes with brightness options ranging from 300 nits to more than 5k nits for high ambient light situations. They can be matrixed for video wall applications, while many have a SoC (system on a chip) as a built-in media player and can include interactivity. Commercial models are available with 24/7/365 duty cycles and typically come with an extendable 3-year parts and labor on-site warranty.
(By the way, if you need a 100-inches-or-under flat panel display, you should probably just buy an LCD — consider the price, resolution, warranty, etc.)
LED provides bright, high contrast, color-saturated images that are seamless. LED is available in environmentally robust (weatherproof) outdoor configurations up to 10K nits of brightness and indoor fine pitch from 800 nits to 5K. Prices are higher than projectors and screens and LCD panels. Prices are closely connected to pixel pitch, which ranges from just under 1mm (MiniLED) all the way to 40mm (DIP). The smaller (finer) the pixel pitch the higher the price. Prices aside (when possible) direct view LED is a hot topic in our industries today.
Let me begin by stating that MicroLED is fascinating technology, for the science and manufacturing aspects as well as the quality of image it can produce. However, for the foreseeable future in digital signage, this will not displace traditional displays such as LCD flat panels and existing fine pitch LED displays. Think of having a car that can do 200 mph, but the speed limit is 70. That being said, the concept and coming reality is on the ascendancy.
According to the Society for Information Display (SID), there are currently over 130 companies involved in some way in the development of Micro-LED displays. The goal is to replace LCD, OLED, and other flat panel technologies beginning in the home and cinema. Suffice it to say that MicroLED at under sub-0.5mm is coming, whether we "need" it or not.
The reason I say this goes back to an argument that originated when 1080P (full HD) ruled the roost and 4K was the new kid on the block. Many articles were written questioning the "need" for 4K relative to visual acuity and cost — and so it is and will be, for some time, for MicroLED. But just as with 4K versus full HD side by side, the enhancements in image quality (brightness, contrast, colorimetry, and efficiency) contrasted with the competitors cannot be denied. The images are simply incomparable. But due to early development issues and high manufacturing costs plus low yield, the prices will remain what some say is "out of sight" for all but the most well-heeled consumers. For your application, it may or may not be considered worth the cost.
As promised earlier, we will talk about a newer version of flat panel technology — newer, at least, from a full color perspective. Many will not be familiar with how E Ink technology works, so I will begin with how their black and white version works, then explain the newest developments in full color.
E Ink displays are "reflective displays." Unlike LCD displays, they use no backlight; rather, ambient light from the environment is reflected from the surface of the display back to your eyes. The more ambient light there is, the brighter the display looks. E Ink screens use tiny capsules filled with black (negatively-charged) and white (positively-charged) particles suspended in a positively-charged clear fluid.
When a negative electric charge is applied to the top of the capsule, the black particles are attracted to the top and become visible. When a positive electric charge is applied to the top of the capsule, the white particles are attracted to the top and become visible. The E Ink screen is made up of millions of these tiny capsules arranged in a grid. The computer sends signals to specific capsules to tell them whether to display black or white. E Ink can also mix black and white to produce grey scales images.
E Ink technology is commonly referred to as "bistable." This refers to the fact that an image on an E-Ink screen will be retained even when all power sources are removed. This means that the display consumes power only when something is changing.
The newest full-color system, from E-Ink uses colored particles to produce a full color gamut like the colors used in inkjet printers. By mixing and "stopping" the particles at different levels, they can use these particles to create up to 50,000 colors. The resulting display renders colors like those in newspapers or even watercolor art.
Philips Professional Display Solutions (PPDS) has announced that it is shipping the Philips Tableaux, the world's biggest full color ePaper digital signage displays with a 25-inch and 32-inch digital signage display. The stated benefits are full color, energy efficient, PoE-capable, easier on the eyes, and environmentally friendly.
The most significant benefit though from a viewer perspective is that the display looks different (in a very good way) and will be noticed. Think of a neon sign versus an electronic sign. You notice the look and feel of the neon — and so it is with full color E-Ink. On the downside, it is more costly than a traditional LCD display, full motion video is not shown due to slower refresh rates, and the sizes are limited — but you can't take your eyes off it.
There you have it — an overview of displays most applicable for digital signage today and some new stuff to ponder. The display is what viewers see while the content is what keeps them looking and — hopefully — engaged. One size or type does not fit all, so plan accordingly — in line with your objectives, viewers' profiles, display location, image size and viewing distance, and the type of display needed to best deliver on your objectives.
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Alan Brawn is the principal of Brawn Consulting, an audio visual and digital signage consulting, and outsourced service provider. Alan’s industry experience spans over 4 decades. He is the past Chairman of the Digital Signage Federation and the Educator of the Year award is named after him. Alan was inducted into The AV Hall of Fame in 2004 and received the Fred Dixon Lifetime Achievement in AV Education from AVIXA in 2015. He was recognized as an AV Living Legend in 2023.
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