An LED wall is not a screen. It’s a few hundred small modules of LEDs with no idea what to display until something tells each one which pixels to light. The controller is that something, and it’s the part of a quotation most buyers skip past.
Skip it and you get a wall that can’t show the laptop input, can’t run at its native resolution, or drops to a black panel on the left whenever the content switches. Every one of those is a processing problem, not a panel problem.
The three parts of an LED control chain
The video processor
This is the box your sources plug into: HDMI from a laptop, SDI from a camera, DisplayPort from a media player, a network stream from a signage system. It scales each input to the wall’s pixel count, lets you crop, split the wall into windows, switch between sources and apply colour correction. On a boardroom wall the processor is what lets you show the video call on the left and the spreadsheet on the right.
The sending card
The sending card takes the processor’s output, one big picture at the wall’s resolution, and chops it into the data streams the panels need. It sends those streams down Cat6 or fibre to the wall. Each sending card has a maximum number of pixels it can drive, and that number decides how many cards a wall needs.
Many modern units combine processor and sending card in one chassis. NovaStar’s VX series and Colorlight’s X series are examples. On a small wall that’s usually the right choice.
The receiving cards
Inside every cabinet on the wall is a receiving card. It takes the data stream for its section of the wall and drives the LED modules in front of it. Receiving cards are daisy-chained from cabinet to cabinet, and the chain is where most wiring faults live.
Processor to sending card to receiving cards to modules. That’s the chain, and each link has a capacity.
Why the pixel count decides everything
A sending card is rated in pixels. A common figure is 650,000 pixels per card at 60 Hz; larger cards carry 2.3 million or more. The wall’s resolution is width in pixels times height in pixels, and that number is set by the physical size and the pitch. The pixel pitch guide explains how to work it out.
Example. A 5 m by 2.8 m wall at P1.86 is about 2,688 by 1,505 pixels, a little over 4 million. A single 650,000-pixel sending card can’t drive it. Either you need several cards, or one large-capacity processor that carries 4 million or more. Under-specify and the wall will only run at reduced resolution or part of it will be dark.
The same count matters for the source. If the wall is 2,688 by 1,505, a 1080p laptop output gets scaled up and looks soft. A 4K source fills it properly. This is why we ask what will be connected to the wall before we quote the processor.
Refresh rate and bit depth
Two numbers on the receiving card side matter for picture quality.
Refresh rate is how many times per second the LEDs are redrawn. At 1,920 Hz a phone camera will catch flicker and rolling bars. At 3,840 Hz it won’t. For any wall that will be filmed or photographed, which includes every stage, showroom and press backdrop, specify 3,840 Hz.
Grey-scale bit depth is how many brightness steps each LED can show. Cheaper cards do 12 bit or 14 bit. Better ones do 16 bit, which is what stops dark scenes from looking blotchy at low brightness. Control rooms running at 20 percent brightness all day need this.
Both are properties of the receiving card and the driver ICs on the module. They’re fixed at purchase and can’t be upgraded later.
What the processor does that a sending card can’t
Scaling. The wall’s pixel count almost never matches the source’s. The processor handles the conversion.
Multi-window. One source full screen, or four sources in quadrants, or a picture inside a picture. A control room running camera feeds alongside a map needs this.
Input switching. HDMI, SDI, DVI, DisplayPort, USB-C and IP streams in one box, selectable from a panel or a tablet.
Colour and brightness control. Lowering a wall from full brightness to 15 percent for an evening function without losing colour accuracy is processor work.
Redundancy. Two processors in hot standby, or dual-link cabling so a cut cable doesn’t black out half the wall. Control rooms and broadcast walls specify this. Showrooms rarely need it.
Sizing the control chain for a project
We work through the same five questions on every wall.
What’s the pixel count of the wall? That sets the sending capacity needed.
What sources, and at what resolution? That sets the processor inputs and whether 4K scaling is needed.
Will it be filmed? That sets the refresh rate.
What’s the lowest brightness it will run at? That sets the bit depth.
Does a failure matter? That sets whether to specify redundancy.
A reception wall showing a looping video from a media player needs an all-in-one processor with a couple of HDMI inputs and enough pixel capacity. A control room wall showing 30 camera feeds and a SCADA screen needs a multi-window processor with redundant outputs and a higher grade of receiving card. Same panels in both cases. Very different control chains.
Control room walls
A control room is the one place where the processor is the most important item in the room. Operators watch it for eight hours, the content is dense, the brightness is low and nothing can go dark during a shift.
Specify a multi-window processor with an operator interface, 16-bit receiving cards, dual power on the processor and redundant data paths to the wall. The control room video wall page covers the room-level requirements.
Conference rooms and boardrooms
Here the processor’s job is simplicity. Someone walks in with a laptop, plugs in USB-C and the wall shows it at the right size. For video conferencing, two windows side by side: the far end and the shared content. An all-in-one processor with auto-switching inputs does this; a separate sending card setup doesn’t.
The conference room LED screen page describes the room setup.
Cabling and the chain of cabinets
Data runs from the sending card to the first cabinet on Cat6, then cabinet to cabinet. Each output port on the sending card carries a fixed number of pixels, so a wall is wired as several chains, each within its port’s capacity.
Three things cause faults here. A chain that exceeds its pixel limit, which shows as the last cabinets in the chain going black. A damaged link cable, which blacks out everything downstream of it. And a receiving card that lost its configuration after a power event, which shows as one cabinet displaying the wrong section of the image.
Specifying loop redundancy, where the last cabinet also connects back to the sending card, means a single cable fault doesn’t take out the chain. It costs one extra cable per chain and we include it on every wall over a few square metres.
Planning an LED wall in Oman
Elite Infotech supplies and installs LED video walls across Muscat, Sohar and Salalah, and sizes the processor and sending capacity to the wall and your sources before anything is ordered.
Call +968 9690 9419 or see the LED video wall page.