LED modules and pixel pitch explained: P2 to P10 LED display modules

What an LED module is

An LED module is the basic building block of an LED screen: a small circuit board, usually 320 × 160 mm or 250 × 250 mm, with a grid of LEDs on the front and driver chips on the back. Modules are fixed side by side into a cabinet or onto a frame, and a screen of any size is made by adding more of them.

The words get mixed up, so here's the hierarchy:

• LED. One light source. In a full-colour screen, each pixel has a red, a green and a blue LED, usually in one package.
• Pixel. One dot of the picture.
• Module. A board carrying a few hundred to tens of thousands of pixels. It's the part that's replaced when something fails.
• Cabinet, or panel. A metal frame holding several modules with their power supply and receiving card, typically 500 × 500 mm, 960 × 960 mm or 600 × 337.5 mm.
• Screen. Cabinets joined together and driven by a controller.

People say "LED panel" for both a module and a cabinet, and "SMD screen" for any modern LED screen. When you compare quotations, check which is meant.

What's on a module:

• The LEDs, soldered to the face in a grid.
• A mask, the black plastic grille around the LEDs that improves contrast and, outdoors, shades them.
• Driver chips on the back, which switch each LED thousands of times a second.
• Data connectors, in and out, so modules link in a chain.
• A power connector, taking 5 volts from the cabinet's power supply.
• Fixings: magnets for front service, or screw posts.
• A label with the pitch, type, batch and date, which matters more than it looks.

What pixel pitch means

Pixel pitch is the distance from the centre of one pixel to the centre of the next, in millimetres. A P10 module has pixels 10 mm apart and a P2.5 module has them 2.5 mm apart. The smaller the number, the more pixels fit in each square metre, the sharper the picture up close, and the higher the price.

The "P" in P10 just stands for pitch.

The number of pixels per square metre follows from the pitch: divide 1,000 by the pitch and square the result. One manufacturer's guide sets it out (Unit LED):

• P10: (1,000 ÷ 10)² = 10,000 pixels per m².
• P5: 40,000 pixels per m².
• P2.5: 160,000 pixels per m².
• P1.25: 640,000 pixels per m².

That squared relationship is the single most useful thing to know about pitch. Halving the pitch quadruples the number of LEDs, and LEDs are most of what a screen costs. It's why P5 is far more expensive than P10, and why choosing a pitch finer than you need is the costliest mistake in buying a screen.

Pitch decides three things:

• How close people can stand before they see dots.
• How much detail the screen can show at a given size.
• The price per square metre.

It doesn't decide brightness, weatherproofing or reliability. Those come from the type of module, covered below.

LED module comparison table: P1.25 to P16

Common LED modules run from P1.25 for boardroom walls to P16 for highway billboards. The table gives typical figures for each pitch from one manufacturer's published module specifications. Other makers' figures differ a little, but the pattern holds: finer pitches are indoor, dimmer and denser, and coarser pitches are outdoor and bright.

The figures are from Colorlit's module specification tables, with the P1.86 resolution from LED Display Factory. Brightness is the maker's stated minimum. Outdoor screens for sunlit positions in Dubai are usually specified brighter than the minimum, at 6,000 to 8,000 nits.

Things the table shows:

• 320 × 160 mm is the standard module size. One supplier lists ten pitches in it, from P1.53 to P10. A common size means cabinets and frames are interchangeable between pitches.
• 250 × 250 mm modules go with 500 × 500 mm cabinets, the format used for P2.6, P2.97, P3.91 and P4.81. Those odd-looking pitches exist because they divide evenly into 250 mm.
• The LED package shrinks with the pitch. SMD3535 means an LED 3.5 mm square. SMD1010 is 1 mm square.
• Indoor and outdoor modules of the same pitch are different products, with different LEDs and about six times the brightness outdoors.

Pixel pitch and viewing distance

The nearest comfortable viewing distance in metres is roughly the pixel pitch in millimetres. A P4 screen looks smooth from 4 metres, and a P10 screen from 10 metres. Closer than that, the eye starts to pick out individual dots. One manufacturer's guide puts the best viewing distance at about three times the pitch.

The minimum and best-distance formulas are from Linsn's viewing distance guide, which also gives a maximum of about thirty times the pitch.

How to use it:

• Measure to the nearest person who needs to read the screen, and choose the pitch at or just below that distance in metres.
• Don't choose from the furthest viewer. Distance is handled by the size of the screen and of the letters, not by the pitch.
• A coarser pitch is fine if nobody comes close. A P10 screen on a rooftop looks as sharp from the road as a P4 screen would, at a fraction of the price.
• Content changes the answer. Video and large graphics forgive a coarse pitch. Small text, spreadsheets and fine logos need one step finer.
• Then check the pixel count. A small screen at a coarse pitch may not have enough pixels to show anything useful. That's covered in the screen arithmetic section below.

Each pitch in plain words

Every common pitch has a job it does well. P10 and P8 are for roads and rooftops, P6 and P5 for walls and forecourts, P4 and P3.91 for shopfronts and halls, P3 and P2.5 for indoor screens seen from a few metres, and P2 and finer for rooms where people sit close.

P10

The classic outdoor module: 32 × 16 pixels on a 320 × 160 mm board, 10,000 pixels per square metre. It's the cheapest full-colour outdoor pitch and the standard for billboards, rooftop screens and anything seen from 10 metres or more. One guide gives its usual viewing range as 10 to 50 metres (Royal Display). Single-colour P10 modules, in red, white or amber, are what scrolling message boards and pharmacy and exchange tickers are made of. See LED scrolling message boards.

Good for: roadside screens, tickers, large facades. Not for: anything viewed from a pavement.

P8

A step sharper than P10, with about 56% more pixels. A good choice for a facade screen across a road or a car park, where P10 looks a little coarse and P6 is more than the distance needs.

P6 and P5

The middle outdoor pitches. P5 has four times the pixels of P10 and suits wall-mounted screens above pavements, petrol station forecourts and site entrances, viewed from 5 to 20 metres. P6 sits between P5 and P8 on price and sharpness.

P4 and P4.81

The usual pitch for outdoor screens people walk past: shopfronts, pylons and totems. P4 gives 62,500 pixels per square metre. Indoors, P4 suits large halls and atriums. P4.81 is the same idea in a 500 × 500 mm cabinet.

P3.91

Probably the most widely used pitch of all, because it comes in the 500 × 500 mm cabinet that suits both permanent walls and stages. Available indoor and outdoor. A sound general-purpose choice for a shopfront, a mall atrium or a mosque hall viewed from 4 metres and more.

P3 and P2.97

Indoor screens for halls, retail and receptions seen from about 3 metres, and outdoor screens for totems and shop windows where people stand close. Outdoor P3 is expensive, since it packs fine LEDs into a weatherproof module.

P2.5 and P2.6

The standard indoor pitch for shops, lobbies and showrooms: 160,000 pixels per square metre, sharp from 2.5 metres. A 4.8 × 2.7 metre wall at P2.5 is full HD. Outdoor P2.5 exists for totems and shop windows viewed from very close.

P2 and P1.86

Meeting rooms, receptions and retail where people stand within 2 metres. From here down, the modules are delicate and the choice of surface, covered below, starts to matter.

Fine pitch: P1.5 and below

P1.53, P1.25 and finer are for boardrooms, control rooms and studios, viewed from a metre or two. They're sold under names like fine-pitch LED, narrow pixel pitch and direct-view LED, and the finest are made as COB. Our LED video walls page covers them.

How to read a module specification

A module specification line packs six facts into a string of codes: pitch, indoor or outdoor, LED package, module size, resolution and scan mode. "P3.91 outdoor SMD1921 250 × 250 mm 64 × 64 1/16 scan" tells you everything needed to compare two quotations or to find a matching replacement.

Scan mode

LEDs on a module aren't all lit at once. The driver lights a fraction of the rows at a time and cycles through them faster than the eye can follow. "1/4 scan" lights a quarter of the rows at any instant, and "1/16 scan" a sixteenth.

A parts supplier's guide sets out the pattern (LED Screen Parts):

• 1/2 and 1/4 scan: outdoor P8 and P10. The LEDs are on for more of the time, so the module is brighter. Fewer LEDs share each driver chip, so it needs more chips per LED.
• 1/8 scan: P5 and P6.
• 1/16 scan: P2.5 to P4.
• 1/32 scan and higher: P2 and finer.

The guide's summary: "The smaller the pixel pitch, the higher the scan ratio required." For a buyer, the point is that scan mode has to match when a module is replaced. A 1/4-scan module won't work in a screen configured for 1/8 scan, even at the same pitch and size.

Refresh rate

1,920 Hz looks steady to the eye. 3,840 Hz is what a screen needs to look clean on camera, with no dark bands. Ask for it on any screen that will be filmed or photographed, which in practice means most of them.

Brightness

Indoor modules give about 600 to 1,200 nits, and outdoor modules 5,000 nits and up. Check that the figure quoted is after calibration, since a screen is usually calibrated down from its raw maximum to make every module match.

What else to ask for

• The LED maker and driver chip, which set the quality more than the pitch does.
• Grey scale, in bits. More bits mean smoother shading in dark scenes.
• Viewing angle, typically 140 to 160 degrees.
• IP rating, front and back, for outdoor modules.
• The batch, so spares match.

SMD, DIP, GOB and COB

These four terms describe how the LEDs are mounted on the module. SMD is the standard today, with the red, green and blue chips in one small package. DIP is the older type with three separate bulb-shaped LEDs per pixel. GOB is SMD with a protective coating, and COB bonds bare chips straight to the board.

• "SMD screen" has become a general name for a full-colour LED screen, since almost all are SMD now.
• DIP is brighter but dated. One guide gives DIP P10 at 7,000 to 10,000 nits against 6,500 to 7,000 for SMD (Royal Display). Modern SMD is bright enough for Dubai sun and looks better, so we specify SMD for new outdoor screens.
• GOB earns its cost wherever hands, bags or cleaning cloths reach the screen.
• COB is for fine pitch. Below about P1.5, it's the more durable choice.

Indoor and outdoor modules: the differences

Indoor and outdoor modules of the same pitch aren't interchangeable. An outdoor module is sealed against dust and water, uses LEDs about six times brighter, and has a deeper mask to shade them from the sun. An indoor module used outside fails in the first rain or dust storm, and an outdoor module used inside is far too bright.

The power figures are from the same manufacturer's tables (Colorlit).

There's a middle category, semi-outdoor, for positions under cover: brighter than indoor, with no real protection against rain. In Dubai we rarely recommend it. Wind-blown dust and humidity reach under canopies, and a full outdoor module costs little more.

For everything else an outdoor screen needs, see outdoor LED screens.

From modules to cabinets: how a screen is put together

Modules are mounted into cabinets, and cabinets are bolted together to make the screen. The cabinet holds the modules flat and in line, carries the power supply and receiving card, and gives the installer something rigid to fix to the structure. A screen is only as flat as its cabinets, and flatness is what makes the joints disappear.

Common cabinet formats:

• 960 × 960 mm, holding eighteen 320 × 160 mm modules. The standard for fixed outdoor screens, in steel or aluminium.
• 500 × 500 mm and 500 × 1,000 mm, holding 250 × 250 mm modules. Die-cast aluminium, light and accurate, used for P2.6 to P4.81 indoors and out.
• 600 × 337.5 mm, a 16:9 shape for fine-pitch indoor walls, so that the wall builds up to standard video sizes.
• 640 × 480 mm and 640 × 640 mm, for indoor walls using 320 × 160 mm modules.
• No cabinet at all. Small screens, tickers and custom shapes fix the modules straight onto a steel or aluminium frame, with power supplies behind. It's cheaper and thinner, and depends on the frame being made accurately.

What to look for in a cabinet:

• Material. Die-cast aluminium is lighter and more precise than sheet steel, sheds heat better and doesn't rust. Steel is cheaper and heavier.
• Service side. Front-service cabinets let modules, power supplies and cards come out from the face, for screens against a wall. Rear-service cabinets need access behind.
• Sealing. Outdoor cabinets have gasketed doors and should be rated for dust and water at the back as well as the front.
• Locks and alignment pins, which pull neighbouring cabinets into line.
• Weight per square metre, which the structure and the wall have to carry.

When a quotation says "P4 outdoor, 960 × 960 cabinet", it's telling you the building block. The screen will be a whole number of those blocks, and its size follows from that.

Working out a screen: modules, resolution and power

To work out a screen, divide its width and height by the module size to get the number of modules, multiply by the pixels per module to get the resolution, and multiply the area by the power figures to size the supply. Screens build in whole modules, so the finished size is always a multiple of 320 × 160 mm or 250 × 250 mm.

Three worked examples

What the examples show:

• The big roadside screen has the fewest pixels. Twenty square metres of P10 carries a fifth of the pixels of six square metres of P2.5. Size and resolution are different things.
• The buildable size is rarely the size asked for. A 6.5-metre screen becomes 6.4 metres. Tell the fabricator the buildable size before the opening or frame is made.
• Maximum power is several times the average. The cable and breaker are sized for the maximum, which is every LED at full white. The electricity bill follows the average.

Is the resolution enough?

• Video and photographs, as a rough guide, need about 300 pixels on the short side to look like a picture. Below that, stick to graphics and text.
• Text needs about 12 to 16 pixels of height per line of Latin letters, and a little more for Arabic. A screen 320 pixels tall holds about 20 lines at most, and far fewer at a readable size.
• Full HD is 1,920 × 1,080. Few outdoor screens reach it, and they don't need to.
• Shape. 16:9 suits video. Wide ribbons and tall totems need content made for them.

Power supplies and cards

Each cabinet has a power supply converting mains to 5 volts, and one supply feeds a handful of modules, how many depending on the pitch and the supply's rating. A receiving card in each cabinet passes the picture data to its modules. When a whole block of modules goes dark together, the power supply or the card is the usual cause, and the modules are fine.

What LED modules and screens cost by pitch

Price per square metre rises steeply as the pitch gets finer, because the number of LEDs rises with the square. A Dubai supplier's published guide puts outdoor P10 screens at about AED 3,000 to 7,500 per square metre, indoor P2.5 to P3.9 at AED 2,900 to 5,500, fine pitch P1.5 to P2.0 at AED 5,500 to 9,000, and COB P0.9 to P1.2 at AED 9,000 to 18,000.

Those ranges are from UP2's price guide and are for the screen, before structure, installation and permits.

Two things in that table surprise people:

• Outdoor P10 costs as much per square metre as indoor P3, despite having a tenth of the pixels. Outdoor modules carry bigger, brighter, sealed LEDs, heavier cabinets and bigger power supplies. Weatherproofing and brightness cost as much as resolution.
• Price doesn't rise as fast as the LED count. Small LEDs are cheaper each, and the cabinet, power and control costs are shared.

Our own guide prices per square metre, supplied and installed:

What else moves the price at a given pitch: the LED and driver chip maker, brightness, refresh rate, the cabinet material, whether it's front service, and how many spares are included. Two quotations for "P4 outdoor" can differ by a third and both be fair, because they aren't the same product. See our LED screen price guide for whole-project costs.

Comparing two quotations at the same pitch

Two quotations for the same pitch and size can differ by a third or more and both be fair, because pitch says nothing about the quality of the LEDs, the driver chips, the cabinet or the power supplies. Compare the lines below before comparing the totals.

1. LED maker and package. The LED is the part that fades. Ask who makes it, and whether it's a gold-wire or copper-wire type. Gold-wire LEDs cost more and cope better with heat and humidity.
2. Driver chip. It sets the refresh rate and how well the screen shows dark shades. Ask for the model and the refresh rate in hertz.
3. Brightness after calibration, in nits, and for outdoor screens whether that's enough for the direction the screen faces.
4. Scan mode. At the same pitch, a lower scan ratio is generally brighter and costs more.
5. Power supply maker and whether there's a spare circuit. Power supplies fail more often than modules.
6. Cabinet material and service side.
7. IP rating, front and back, for outdoor screens.
8. Control system: the sending box or processor, and the software.
9. Spares included, as a number of modules, power supplies and cards, from the same batch.
10. Warranty, and what it covers: parts only, or parts and labour on site.
11. What's left out. Structure, electrical supply, permit, crane and content are the usual gaps between a low price and a full one.

Ask each supplier for the module's specification sheet. If two sheets show the same pitch but different LED packages, scan modes or brightness, you're comparing different products, and the cheaper one may be the right choice or the wrong one depending on where the screen is going. A screen in a mall doesn't need the LEDs a west-facing facade does.

How long modules last, and what wears them out

Manufacturers quote LED lifespans of about 100,000 hours to half brightness. In Dubai, heat is what shortens that. An outdoor module run hard in direct summer sun ages far faster than the same module indoors, and the first sign is uneven brightness across the screen, well before anything stops working.

What wears modules out:

• Heat. The hotter an LED runs, the faster it dims, and red, green and blue fade at different rates, so colours drift. The top of a screen, where warm air collects, usually goes first.
• Running at full brightness. A screen with headroom, run at 60 to 70% of its maximum, lasts much longer than one run flat out.
• Humidity and salt. Moisture gets into LED packages and corrodes them from inside, which shows as dead pixels in clusters. Near the coast, sealed modules with coated boards matter.
• Dust. It blocks ventilation and holds heat.
• Static images. LEDs that show the same bright logo all day age ahead of their neighbours, leaving a ghost of the image.
• Physical damage. On fine-pitch indoor screens, knocks from ladders, bags and cleaning are the main cause of dead pixels.
• Power quality. Surges and unstable supply kill driver chips and power supplies. Surge protection is cheap.

What keeps them going: good ventilation or cooling, automatic dimming at night, regular cleaning, running below maximum, and replacing failed power supplies and fans promptly so that neighbouring parts aren't overloaded.

A realistic expectation for a well-specified outdoor screen in Dubai is many years of service with a small number of module and power supply replacements along the way, and a recalibration every year or two to keep it even. An indoor screen in air-conditioning has a much easier life.

Replacing modules on an existing screen

A failed module can be replaced on site in minutes, but only with one that matches the original in pitch, size, LED type, scan mode and hole positions, and ideally from the same production batch. A module that fits but comes from a different batch will show as a patch of slightly different colour or brightness.

We replace modules, power supplies and receiving cards on site, and repair modules at the bench, on screens we installed and on screens installed by others.

Why new modules don't match old ones

• Batches differ. LEDs are sorted at the factory by colour and brightness. Two batches of the "same" module can be visibly different side by side.
• LEDs age. After a few years in the sun, the modules on your screen are dimmer than new ones.
• Models change. A module made three years ago may no longer be produced, and its successor may have a different driver chip or scan mode.

This is why spare modules should be bought with the screen, from the same batch, and kept. It's the cheapest insurance in the whole project.

What we can do when there are no spares

• Recalibrate. Adjust the new module's brightness and colour to sit closer to its neighbours.
• Move modules. Shift old modules from the edge into the middle and put the new ones at the edge or bottom, where a difference is least noticed.
• Repair the original. Many faults are a single failed LED, a driver chip or a connector, which can be replaced at the bench so the original module goes back in.
• Replace a section, when a screen is old enough that a patch can't be hidden.

What to send us

Before we visit, a few photographs save a wasted trip:

1. The label on the back of a module, showing pitch, model, batch and date.
2. The back of the module, showing the connectors and driver chips.
3. The fault, with the screen on. A dead block, a line, wrong colours or a single dark pixel each point to a different cause.
4. The whole screen, so we can see its size and how it's reached.
5. The controller or sending box, and its brand if you know it.

Reading the fault

Mistakes to avoid

Most pitch mistakes come from buying on the P number alone.

1. Choosing a finer pitch than the nearest viewer needs.
2. Choosing a coarse pitch for a small screen, leaving too few pixels to show anything.
3. Comparing quotations by pitch only, ignoring LED type, brightness and refresh rate.
4. Using indoor or semi-outdoor modules outside.
5. Fixing the opening size before the buildable size is known.
6. Sizing the power supply from the average figure.
7. Buying no spare modules.
8. Ordering a replacement by pitch and size only, without the scan mode and model.
9. Mixing batches across the middle of a screen.
10. Exposed fine-pitch SMD modules within reach of the public.
11. Assuming a dark block means dead modules, when it's a power supply.
12. A low refresh rate on a screen that will be filmed.