LED pixel pitch and viewing distance for a shop window sign

The rule: one millimetre of pitch buys one metre of distance

Pixel pitch is the centre-to-centre spacing of the LEDs, quoted in millimetres: P4 means 4 mm. Finer pitch packs more LEDs into the same area and pulls the safe viewing distance in with it. Read the pitch as metres and you have the closest distance at which the picture holds together; for images that should look smooth, budget two to three times that distance.

Across the same wall area, here the 1.54 x 0.77 m wall the example below builds, the pixel count climbs with the square of the pitch ratio:

Finer-pitch modules are physically smaller. A 64 x 64 module measures 256 mm square at P4 and 160 mm square at P2.5, so the same wall area takes more modules, more wiring and more controller capacity.

Worked example: a 6 x 3 P4 wall facing a pedestrian street

Inputs:

• 18 LED modules, each 64 x 64 pixels at P4 pitch (4 mm), laid out 6 across and 3 high.
• Readers: pedestrians at the glass about 2 m away, usual viewing 15 m, and the message must stay readable to 30 m.
• Legibility planning figure: 30 ft of viewing distance per inch of capital height (FHWA), with 20 ft per inch as the fast-reading figure.
• Content: a product photo with a name and a price.

Rules in words: wall size comes from module size times count, pixel count from module pixels times count, minimum viewing distance from the pitch, and letter height from the viewing distance.

The arithmetic:

1. Module size: 64 x 4 mm = 256 mm square.
2. Wall size: 6 x 256 mm = 1,536 mm wide, 3 x 256 mm = 768 mm high. The diagonal is the square root of (1,536² + 768²) = the square root of 2,949,120, about 1,717 mm, or 68 in.
3. Pixels: 6 x 64 = 384 across and 3 x 64 = 192 high, so 384 x 192 = 73,728 px. A 1080p screen has 2,073,600 px, 28 times more; a 4K screen has 8,294,400, 112 times more. The wall's 192 lines put it in old arcade-game territory.
4. Minimum viewing distance: pitch 4 mm, so 4 m. A reader at 2 m stands well inside it.
5. Letter height: at 30 ft per inch, 1 m of distance buys 25.4 ÷ 9.1 = 2.8 mm of capital height. At the usual viewing distance that is 42 mm; at 30 m it is 84 mm.
6. In pixels on this wall: 42 ÷ 4 = 10.5 px capitals at that nearer distance, and 84 ÷ 4 = 21 px at 30 m. A 5 x 7 dot matrix character is the legibility floor; 10 to 12 px capitals read quickly. The fast-reading size, 63 mm, is about 16 px.

Result: at both far distances the wall carries a product name and a price in big block type at daylight brightness. Under 4 m, including everyone at the glass, it is a dot matrix, and a photo breaks up on it.

Decision: if the closest reader stands nearer than the pitch number in metres, that pitch is wrong for pictures. The glass here is at 2 m against a 4 m pitch, so this wall is a text sign. Pictures at the glass need P2 or finer, or an LCD.

Four ways to fill the window, side by side

The TV wall row: four 55 in 16:9 screens make about 2.44 x 1.37 m, 110 in on the diagonal, and 3,840 pixels across 2.44 m is a 0.63 mm pitch. The splicing controller takes one HDMI or DVI input and drives the four screens from it.

Where each option wins

• The P4 wall wins for a message read from across the street: capitals land at 10 to 21 px on it, legible block type in full daylight.
• P2.5 wins when readers stand at the window and you want LED brightness anyway: 2.56 times the pixels of P4 in the same frame, clean from 2.5 m.
• The TV wall wins indoors, out of direct sun, when pixel count matters more than seams: 4K from four consumer panels and one controller.
• One commercial LCD wins at 60 to 65 in with photos and video: 4K in a single sheet, 112 times the pixels of the P4 wall. The consumer TV or commercial display comparison covers the build differences, and shop window brightness in nits gives the number a window actually needs.

What to ask for when you buy LED modules

• The pitch in millimetres and the module pixel count. Multiply modules across by pixels across on paper before you pay, so the finished wall resolution is no surprise.
• The controller type. A PC-fed controller takes a video feed over HDMI or DVI and maps a region of it onto the panels, so your slideshow runs on the feeding computer. A standalone controller plays the scrolling text you load through its own software and little else. Either way, set the feeding device to the exact pixel resolution the controller expects, or the wall crops the wrong corner of the picture, the failure you see on crashed billboards.
• The brightness in nits, matched to your glass and the direction the window faces.
• Modules, controller and power supply as one matched set from one vendor, with the DC wiring and the wall frame done to your local electrical code. A window wall carries weight and current, and both belong in the install plan.
• For the PC-fed route, any player with an HDMI output can feed the controller, the way an LED video wall is driven from a signage player.

The decision

• Text and prices, read from that far pavement distance and beyond: the P4 wall passes. Size capitals at 42 mm for the usual viewing distance and 84 mm for 30 m, use whole words, and accept the dot look up close.
• Photos or video, with readers at the glass: pick the pitch from that closest distance, 2 m means P2 and 2.5 m means P2.5, or switch to one high-brightness LCD.
• The biggest picture indoors, away from daylight: four 55 in TVs and a splicing controller, accepting the bezel cross.

Recommendation: For a pedestrian street where people stop 1 to 3 m from the glass and the content is a product photo with a price, use one high-brightness commercial LCD around 60 inches, or an LED wall at P2 or finer when daylight brightness outweighs pixel count. Keep the P4 wall for text read from 15 m and beyond. The displays section covers wall, counter and hanging signage displays, with larger wall models quoted per project.

Questions