A first and easy criterium, is the size of the control room. For small rooms, LCD is generally the preferred technology. The panels are quite shallow, so the real estate space taken by the video wall is quite limited. What’s more, LCD is also ideally suited for short viewing distances (providing an excellent visual experience even when watched from up close. Good viewing angles () ensure that every operator can comfortably see the content on the video wall, even when they are positioned at the edges of the room. If interactivity is needed (which is most often the case in smaller rooms with a limited number of operators), then LCD video walls are the best option as well.

Rear-projection cubes feel most at home in larger rooms because they need more depth. Operators will have the best optical experience when looking quite straight at the wall. So a mid-sized to large control room, in which operators are positioned a bit further from the wall, is ideal for RPCs.

Direct view LED video walls are also at their best in slightly larger rooms. They are very shallow, so take up very little real estate space, but require a bit more viewing distance, depending on the pixel pitch, for the best effect. A 1.2 mm pixel pitch model, for example, is best viewed from about 3 meter / 9.6 feet. By the way, the optical performance of LCD video walls does not restrict them for use in small walls: they are suited for use in larger rooms as well!

In the past, control rooms were typically dark and gloomy places, with little ambient light that could interfere with the content displayed on the video wall. Improved brightness of the video wall however changed this mindset. Especially direct view LED video walls can produce a lot of brightness and are effective in even the brightest lighting conditions. Furthermore, this technology also suffers minimally from so-called ‘specular reflection’ (in other words, it does not reflect light coming from lamps or windows like a mirror would).

Traditionally, the light output of LCD and (especially) rear-projection cubes is lower than that of LED. Typically, LED rear-projection modules have a brightness of about 400 nit, whereas LCD video walls produce 500 nit. However, the RGB Laser ODL series (RPC) and Barco UniSee (LCD) have successfully countered this disadvantage and boost the highest brightness in the markets, to 720 and 800 nits for their respective technologies. In other words, these products are also suited to be used in challenging lighting conditions. Be aware that LCD tends to reflect light most of the technologies, so this is something to take into consideration when positioning the lamps in the control room.

Next to the overall ambient lighting conditions, also the positioning of the light sources is important. There is a big difference between LCD, RPC and LED video walls when it comes to reflections.

First of all, there are two dominant types of reflection: specular and diffuse (Lambertian). The first is the one we know from a mirror: the light comes in and is reflected for 100% into one direction. Diffuse reflection is exactly opposite: the light is reflected equally into ALL directions. A piece of white paper is an example of a diffuse reflector.

For video walls, reflection can be an important parameter, and can hinder the viewing experience of the operators. That’s why it needs the proper attention.

LCD video walls act most like a specular reflector. This means that a clever way of positioning the lamp points is needed. In most cases, this is not a big issue: just make sure the lamps are not directed towards the video wall, and most interference will be blocked. Direct view LED, on the other hand, acts like a diffuser. For these video walls, the rule is: the darker the room, the better the contrast.

RPCs act both a little like a diffuser and as a reflector, but the reflected amount of light is limited. This makes them a good solution for rooms with fixed lamp points and windows, where the lighting conditions cannot be adjusted to the video wall.

The previous chapters primarily discussed the physical features of the control room. But the content you want to use on the video wall is of course extremely important as well. In this area, the inter-screen gap or bezel width is a significant parameter. These create black lines around all individual displays, making the video wall look rasterized. If the content consists of multiple windows that are ‘boxed’ inside the individual displays, then this is no problem whatsoever, and the black lines will be barely visible. However, in some markets, like utilities and process control, typically a single (SCADA) application is spread across the entire video wall. This means that the black lines will run across the content, interrupting the seamless viewing experience. If the background is black – which is often the case – these lines will not be visible. However, the content will still be interrupted, which is especially an issue when running through alphanumeric data.

Of the three different technologies, LED is the only one that is completely seamless. Whenever an ensured interrupted viewing experience is needed, this is the preferred technology. Traditionally, LCD video walls have the most pronounced interruption between screens and are most commonly used with ‘boxed content’ applications, e.g. to monitor video-centric security and surveillance footage. Note however that Barco UniSee is the LCD video all with the smallest inter-screen gap in the market today, which opens many more possibilities for LCD panels. Rear-projection cubes have a small inter-screen gap, which is barely noticeable and is therefore suited for any application. The fact that this technology does not suffer from burn-in effects (which LCD video walls do), makes it very suited for very static SCADA-like content (used in the Utilities market), with dominantly dark backgrounds.

Even though Barco video walls are designed for the long haul, there will come a time that replacement becomes necessary. You then have 2 options: replace the complete video wall structure or look for ways to re-use parts of the existing wall. Mind you, we are not talking about replacing one tile of the wall, but the whole shebang.

If you are interested in recuperating part of your existing installation, then rear-projection is likely the best option. This technology consists of a projection module, and a structure with screen. The structure is very solid and not likely to wear out. That is why Barco offers upgrade kits, consisting of the projection module (and the necessary inputs). This makes upgrading much faster, cheaper, and more ecological. Because no large construction works need to be conducted, an upgrade will hardly interrupt the day-to-day operations.

For LCD and LED, the upgrade possibilities are more limited. When compatible, the mounting structure can sometimes be recuperated.