If you understand one specification before buying LED, make it this one. Almost every other choice falls out of it.
Pixel pitch is the distance between the centre of one LED pixel and the next, measured in millimetres. A "P2.5" panel has 2.5 mm between pixels; a "P10" has ten. Smaller pitch means pixels packed more tightly, which means finer detail and the ability to stand closer without seeing the individual dots — and, because tighter packing needs far more diodes and far more precise manufacturing, a steeply higher price. Pitch is not a quality grade where smaller is simply better; it is a match to be made. A fine pitch on a wall nobody stands close to is money set on fire, and a coarse pitch on a wall people study is a blurry disappointment. The number is only right relative to where the viewer stands.
The useful rule of thumb is that the minimum comfortable viewing distance, in metres, is roughly the pixel pitch in millimetres — so a P3 wall looks clean from about three metres and up, a P10 from about ten. Stand closer than that and the image visibly breaks into dots; stand much farther and you are paying for resolution your eye cannot resolve, where a coarser, cheaper pitch would have looked identical. This is approximate and there are more precise formulas based on visual acuity, but the rough version is enough to catch the two expensive mistakes: specifying too fine for a far wall, and too coarse for a close one. Before anyone quotes a pitch, the honest first question is "how close will the nearest regular viewer be?" — and the answer sets the floor.
The common upsell is finer pitch than the viewing distance needs, sold on the feeling that smaller numbers are better. For a wall across a lobby or a plaza, resist it; the eye cannot tell, and the budget is better spent on brightness, reliability and spares. The upsell worth accepting is the opposite case people under-spend on: walls that will be photographed or appear on camera, where moiré and the camera's unforgiving sensor effectively demand a finer pitch than the naked eye would, and walls where viewers will sometimes approach closely even if "normally" they do not. Specify for the closest realistic viewer and the camera, not the average one. Getting pitch right is the difference between a wall that looks intentional and one that looks like a mistake at every distance.
Buyers often start from "I want 4K." On LED, resolution is simply pitch multiplied across physical size — a given pitch over a given wall yields whatever pixel count it yields, and chasing a headline resolution by going finer on a far wall is the same money mistake in different clothing. Start from viewing distance, derive the pitch, let the physical size and the resolution be the outputs. Done in that order, the wall looks right and costs what it should. Done backwards — resolution first — it usually costs more and looks no better, which is exactly the result a weak supplier is happy to sell.
03 — Indoor vs outdoor LED →