Chapter 04 · Hardware and selection
The right technology
Professional display or television, candela, pixel pitch, player and bracket: what sets devices apart and which data-sheet figures actually matter.
A furniture store called us in July: the large screen in the entrance was black, for the third time in two weeks. Nothing was broken – the unit was a television from an electronics market, built for three hours of evening programming, and since March it had been running twelve hours a day in portrait next to a glass façade. It had shut itself down to save itself. Technology rarely decides whether something looks good, but whether it still runs in three years.
Professional display or television
The question comes up in almost every conversation, and it is a fair one: a television costs less and has the same diagonal. The difference is not in the picture but in everything that comes afterwards.
| Feature | Consumer television | Professional display |
|---|---|---|
| Operating hours | a few hours a day | 16/7 or 24/7 |
| Warranty in continuous use | usually excluded | for commercial use |
| Portrait format | not approved | approved, heat management suits |
| Brightness | 250 to 400 cd/m² | 350 to over 5000 cd/m² |
| Housing | plastic, stand | metal, VESA, wall mount |
| Remote management | remote control | network, RS-232, CEC, schedule |
| After a power cut | stays off or in the menu | starts back into playback |
Then there are details that only hurt in everyday use: a channel logo burning itself into the panel as image retention, advertising on the home screen, no remote shutdown for a hundred devices. For a meeting room used twice a week, a television is fine. For anything showing the same picture for hours every day, it is the more expensive route.
Brightness in candela
Brightness is given in candela per square metre, often called nits. It is the one figure on the data sheet where a wrong choice is immediately visible – to everyone, every day.
| Location | Guide figure in cd/m² |
|---|---|
| Interior with artificial light, practice, corridor | 350 to 500 |
| Bright room, window to the side, lobby | 700 to 1000 |
| Shop window behind glass | 2500 to 4000 |
| Outdoor surface in direct sun | from 4000, better 5000 |
Aim too low and you do not get a slightly weaker picture but no picture at all: the display looks grey, colours tip over, text disappears into the reflection. Turning it up does not help, the maximum is already reached.
Conversely, too bright is no goal either: a shop-window unit at full power in a waiting room dazzles and ages faster. The right choice is a device that manages the peak and can be dimmed by sensor or schedule. Check whether the figure applies to the panel or to the finished front: safety glass and film swallow brightness.
Panel, resolution and format
Four K sounds like the better choice but rarely decides anything: whether you see more resolution depends solely on the viewing distance. On a 55-inch screen from four metres the eye no longer resolves the difference from Full HD. Four K becomes worthwhile where people come close: touch totems, menu boards above the counter, diagonals from around 86 inches.
More important than the pixel count are three other properties:
- Viewing angle: an IPS panel keeps its colours from the side, cheap VA panels go flat. Anyone walking past almost always sees it at an angle.
- Anti-glare: a matte surface rescues more locations than extra brightness.
- Still images: professional panels have countermeasures against image retention, such as pixel shift.
For format, what the chapter on location says applies: the content decides – but be consistent. An installation of identically oriented devices saves every second hour of design work.
Playback device: SoC or external player
Every professional display today has a computer built in, the system on chip, SoC for short. The signage software runs directly on it – for most installations the right choice: one device, one cable, no second source of error, no signal loss, no fan.
An external player becomes necessary if one of these applies:
- Processing load: elaborate animations, several videos running at once, very large surfaces.
- Special software: an industry application or an integration that exists only for Windows.
- Touch: kiosk applications with forms or search respond noticeably more smoothly.
- Several zones on one picture, for example occupancy, weather and video at the same time.
- LED walls, which need their own signal processing anyway.
Check before buying how long the manufacturer will supply the SoC with updates. A display lasts ten years; a platform often demands a newer runtime environment after five – and then a small player is the cheaper extension.
The LED wall
An LED wall is not a large display but a component made of many modules. Its most important measure is the pixel pitch: the distance between two image points in millimetres. Rule of thumb: the minimum viewing distance in metres corresponds roughly to the pixel pitch in millimetres.
| Pixel pitch | Minimum distance | Typical use |
|---|---|---|
| 1.2 mm | from about 1.2 m | meeting room, reception |
| 2.5 mm | from about 2.5 m | sales floor, foyer |
| 3.9 mm | from about 4 m | hall, entrance area |
| 6 mm and more | from about 6 m | façade, outdoor advertising |
Indoor and outdoor modules differ in brightness and encapsulation; an indoor module outdoors will not survive a winter. Before ordering you also have to decide:
- Maintenance access from the front or the rear. Without either, every module change becomes a building site.
- Spare modules: two to three per cent of the surface in stock, from the same production run; buying later means colour deviation.
- Power draw: a wall pulls several times its average at peak, and the supply is dimensioned for that.
- Frame construction: the substructure must be level, otherwise module edges show up in the picture.
Touch, kiosk and operation
As soon as people are meant to touch a device, the requirements change: a touch display is not a display with an extra function, it is a piece of furniture.
Capacitive surfaces respond like a smartphone: precise, glass, easy to clean – but they need a bare finger and fail with gloves. Infrared touch works with a light grid in front of the panel, works with gloves and a stylus and is cheaper at large diagonals, but becomes less accurate at the edges.
Just as important is the operation itself:
- Operating height: the active area belongs between roughly 0.90 and 1.20 metres above the floor; any higher and it is out of reach for seated people.
- Accessibility: approach space for wheelchairs, large buttons, sufficient contrast. In public buildings this is not optional.
- Hygiene: in practices and restaurants a surface that tolerates disinfectant counts.
- Return to the idle state after a minute, otherwise the next person sees what the previous one typed.
And reckon with people who press rather than tap: the mount must not wobble.
Bracket, enclosure and the underrated accessories
The mount is where people most often save money, and it causes the most trouble. What counts is the VESA standard, meaning the hole pattern on the back, and the permitted load – checked against the device weight, not against the diagonal.
- Wall construction: concrete and brick carry directly, plasterboard only via studwork, insulation not at all.
- Service access: a tilt-out mount saves a second person at every intervention.
- Cable routing: power and network into the wall or into a trunking; a bundle of cables devalues any good design.
- Theft protection: security screws, a locked mounting plate, and on totems a lockable service hatch.
The accessories forgotten in quotations that wreck deadlines:
- Cable lengths: HDMI becomes unreliable beyond about ten metres; above that you need active cables, fibre HDMI or network cable.
- The socket behind the device. It is missing more often than expected, and an extension lead across the wall is not a solution.
- Switching times via the display's own schedule rather than via a mechanical timer.
- A UPS where power cuts are frequent.
- Network: cable beats wireless. Wifi is the most common reason for screens standing still.
What really saves money on hardware
In digital signage the saving is not made at purchase but over the running time. The installations that cause us the least work almost always share the same characteristics.
- Standardisation: one product line, one type of mount, one playback path. Anyone with nine device types across twelve sites needs nine sets of instructions.
- The same models across sites: a change is tested once instead of nine times.
- A spare unit in stock: a display in the cellar brings a failed site back within hours instead of weeks. The same applies to LED modules.
- Remote maintenance: devices that can be switched, restarted and monitored over the network save most of the call-outs.
- Think in service life, not purchase price: a device built for continuous operation lasts twice as long as one used against its purpose. The second purchase is the most expensive.
- Night-time dimming: an installation that is dark at night uses less power and ages more slowly.
The most honest question before buying is therefore not what a device costs, but how often somebody will have to drive out – more on that in the chapter on software and maintenance.
Key pointThe most expensive installation is the one someone has to drive out to: choose technology by how it will be run, not by the data sheet.