LED, video wall and projection

Pixel pitch is the distance between the centres of two adjacent pixels on an LED panel, measured in millimetres. A smaller value looks sharper close up, and costs more.

The “so many mm equals so many metres” rules circulating online are each a manufacturer’s own advice, and they differ markedly:

Source	Rule	For 1.25 mm
Christie	pitch (mm) × 8 = optimum distance (feet)	~3 m
Planar	pitch (mm) × 10 = feet	~3.8 m
Absen (as reported in 2017)	1 mm = 1 m	~1.25 m
LG (as reported in 2017)	~3.5 ft per mm	~1.3 m

That is a threefold spread. AVIXA has no standard specific to pixel pitch and viewing distance, so these are guidance, not a standard.

What actually decides it: how close the nearest viewer is, what the content is (a large-type announcement and a detailed table do not ask the same thing), and the budget. The smallest pitch is not automatically right — at six metres nobody sees the difference between 1.2 mm and 1.9 mm, while everybody sees the difference in price.

Because we work brand-independently, we measure the space and advise from the content rather than applying one manufacturer’s rule.

This is not a question to answer by eye, and there is a standard for it: AVIXA’s DISCAS standard (ANSI/INFOCOMM V202.01:2016) derives display size from the farthest viewer and the type of content.

For detailed content such as tables and drawings, the Analytical Decision Making formula is:

image height = vertical resolution × farthest viewer distance ÷ 3438

(3438 is a constant derived from 20/20 visual acuity.)

An example shows why it matters: with 1080p content and the farthest viewer at 6.7 m, the required image height is ~2.1 m — about 169 inches at 16:9. The 98-inch panel that usually gets specified for a meeting room is ~1.2 m high, and falls short in that scenario.

“Is our screen too small?” is answered by that calculation, not by estimate. Measuring the farthest seat and agreeing the content type is enough to run it.

Note: AVIXA’s current standards list now shows ANSI/AVIXA V202.01:2026. The formula above is from the 2016 edition; we have not verified what changed in the 2026 one.

These are two different effects that get confused, and they have different fixes.

Flicker and banding. This happens when the LED’s refresh timing does not match the camera’s shutter. Brompton treats genlocking the source, camera and LED processor as mandatory, and notes that LED refresh timing can be tuned to the camera settings. It is a configuration problem solvable with the right equipment.

Moiré. This is an optical effect from the clash between the camera sensor’s pixel grid and the LED’s pixel pitch — nothing is wrong with the wall; the artefact forms in the camera. Panasonic’s recommendations:

• Move the subject as far from the wall as possible
• Open the aperture to reduce depth of field (with an ND filter if needed)
• Use a longer focal length
• Choose the smallest pixel pitch the budget allows

That last point feeds the purchase decision: for a wall that will be shot, pitch is chosen with the camera in mind as well as the audience. On conference halls, TV studios, events and XR projects this has to be settled up front.

Manufacturer sources map symptoms to causes, and that mapping shortens diagnosis considerably:

Symptom	Likely cause
One cabinet entirely dark	Power supply or receiving card failure
Dark modules, missing rows or columns	Loose power connectors, faulty ribbon cable, signal cable failure or wrong connection
A colour missing on a module	Poor signal cable connection or a faulty module
Colour inconsistent along one row	Driver IC failure
The whole wall blank	Sending card communication, the source signal, or configuration errors such as brightness left at 0%

That last row matters: a share of “the whole screen is gone” calls are configuration rather than hardware. Brightness stuck at zero, or a source that has dropped, looks identical to a dead wall.

Daktronics also notes that unauthorised repair can void the warranty — worth knowing on a wall still in its warranty period, however simple a module swap looks.

What speeds the work up in practice is spares: a few modules from the same production batch and one spare card turn most faults from hours into minutes.

LEDs absorb moisture from the air when they are not used. Heat a damp LED quickly and it can be damaged, leaving a column that stays lit regardless of the content — the industry calls this the caterpillar effect.

The remedy is to warm a long-idle wall up gradually, starting at low brightness. The schedule Christie publishes for its own Core III product shows what that means in practice:

When it is needed: at first installation; in environments above 60% relative humidity; after more than 2 days unused in high humidity or 10 days in low humidity.

Schedule: over 24 hours, at two-hour intervals, brightness at 5, 8, 10, 15, 20, 25, 35, 45, 60, 70, 80, 100%.

Daily use: at least 4 hours. Where there is no daily use and humidity is below 60%, at least three 4-hour runs a week; above 60%, standby at low brightness.

Storage: indoors and dry, between -10 and 50 °C, in moisture-proof antistatic bags with fresh desiccant.

These figures are Christie’s, for their own product. Always follow the manufacturer’s manual for the screen you have.

For seasonal halls, hotels and exhibition screens this is an operations matter rather than an installation one — and it gets missed because nobody mentions it.

There are two different causes, depending on the technology.

On an LCD video wall: panel edges can read darker than the centre, and brightness and colour temperature vary between panels. NEC addresses this with sensor-based calibration software — it is a difference software can correct.

On LED: different production batches differ in colour and calibration. Spare modules should therefore come from the same production batch, or be colour-matched after fitting. A module of “the same model” bought a year later can produce a visibly different white.

The practical consequence is a purchasing one: buying the spare modules at the same time and from the same batch as the wall settles the problem before it happens. We recommend it as standard on our projects.

Calibration is not a one-off either: panels drift over time, so periodic calibration is part of keeping a large wall looking like one surface.

Specifications usually quote life in hours — 100,000 for Planar’s DirectLight Pro HD 137, for example. But the figure does not mean what it is usually taken to mean: it is “to half brightness”. The wall does not fail at that point; its brightness has fallen to half of what it started at.

The same specification gives operating conditions of -20 to 40 °C and 10-80% relative humidity, non-condensing. Run a wall outside those and the quoted figure stops being relevant.

Christie’s note is directly operational: running the screen at lower power and brightness extends its life. Most indoor walls run brighter than they need to — which tires the eye, shortens the life and wastes electricity at the same time.

What protects the investment, then, is not buying a more expensive wall but setting the brightness properly and maintaining it. A brightness set to the ambient light at commissioning pays for itself over the years.

There are cases where each of the three is right. The question is not which is “best” but which suits this job.

LCD video wall. Christie puts the initial cost markedly lower, and notes that sub-millimetre bezels become negligible at viewing distances of 3 m and beyond. Against that, the operational life is shorter. It suits projects that do not run 24/7 and where image quality is not the first priority.

LED. A seamless surface, high brightness and contrast — no bezels. Against that, it generally draws more power and needs more cooling than LCD, and both belong in the budget from the start.

Projection. Commercial Integrator’s assessment is that above 98 inches, budget permitting, projection or dvLED deserve consideration. There is a limit to how large a single panel goes, and beyond it the argument is between those two.

Because we work independently of brand and technology, we take this decision from the space: ceiling height, ambient light, viewing distance, hours of use and budget. Without all five on the table at once the answer does not come out right.

You can — as long as you know what you are buying. Samsung’s comparison puts the difference plainly: consumer TVs are designed for a few hours a day, while professional displays are built for 16/7 or 24/7 operation and add remote management and protection against tampering.

A screen in a hotel lobby or a shop window, switched on in the morning and off at night, runs far beyond the duty profile a consumer TV was designed for. The difference usually shows up not in the first six months but in the second year.

Remote management is not a minor point either. Across ten screens, walking to each one to switch it on and fix its input becomes the real cost over time.

One point to check on the warranty side. LG Türkiye’s extended warranty terms exclude “faults arising from the use in commercial businesses of a product designed and manufactured for home use”. We could not verify whether standard manufacturer warranties carry a similar clause, so it is worth reading the warranty text for the specific product before buying.

On a projector that shuts itself down, Epson’s troubleshooting points first at the vents and the air filter. A blocked filter stops the unit cooling and it shuts down to protect itself. The filter needs cleaning or replacing — and it is one of the jobs nobody puts in a calendar after handover.

“Laser projectors need no maintenance” is half true. Epson quotes 20,000 hours for the laser light source (to 50% brightness) and states that no maintenance is required for the light source over that period. In the same place it adds that parts other than the light source may need replacing sooner.

So lamp replacement goes away; maintenance does not. Filters, optical surfaces and cooling still need periodic attention.

Whether to keep an older lamp-based projector running or move to LED is a decision taken from the hours of use and the ambient light — we work the two out together.