An LED display is composed of many small diodes that emit light individually.

These diodes can either be powered statically (all on at once) or through multiplexing — a time-division method where groups of LEDs are rapidly switched on and off in sequence.

The human eye perceives the image as stable because this switching happens faster than our visual system can detect.

Technically, the higher the multiplex ratio (e.g. 1/6), the fewer LEDs are active at any given time.

Drive Modes Explained

Full Scale (Static Drive / 1:1)
Each LED has its own dedicated current path and can remain continuously lit.
→ Maximum brightness and image stability, minimal flicker.
→ More expensive and power-hungry because every LED requires its own circuitry.

Static 1/2 Scale (1:2 Multiplex)
Two LEDs share one driver channel; only one is active at a time.
→ Lower brightness than full scale, but cheaper to produce.

Static 1/3 Scale (1:3 Multiplex)
Three LEDs share a single channel, one active at a time.
→ Brightness decreases further, but cost also drops.

Static 1/6 Scale (1:6 Multiplex)
Six LEDs share one driver channel.
→ Significantly reduced brightness, higher risk of flicker, weaker contrast — especially if refresh rate is not high enough.
→ Cheaper and consumes less power.

Advantages and Disadvantages

Full Scale (1:1)
✔ Highest brightness, quality, and image stability
✘ Most expensive, higher power consumption, more space for circuitry

Lower Ratios (1/2, 1/3, 1/6 …)
✔ Lower cost and energy use
✘ Reduced brightness and image quality — problematic for outdoor displays in bright sunlight
✘ Higher risk of visible flicker, especially noticeable when filmed with a camera

Practical Guidelines

• Outdoor LED screens: Brightness is king → the closer to full-scale drive, the better.

• Indoor screens: Lower drive ratios (e.g. 1/3 or 1/6) can be acceptable since ambient light levels are lower.

• Broadcast or camera use: Avoid high multiplex ratios (e.g. 1/6) to prevent visible flicker on video.

In short:
Full scale = quality and brightness, but more expensive.
1/6 = energy-efficient and cheaper, but less visually stable.

What is Refresh Rate?

The refresh rate measures how many times per second the screen redraws the image — expressed in Hertz (Hz).

For example:

• 1920 Hz → the image refreshes 1,920 times per second

• 3840 Hz or 7680 Hz → high-end professional standards

A high refresh rate ensures a smooth, flicker-free image for human eyes and prevents black bands or “banding” when the display is filmed with a camera.

How Drive Mode and Refresh Rate Are Linked

Multiplexing means each diode is only powered for a fraction of the total cycle.

Example:
At 1/6 drive, each diode is active only one-sixth of the time.
To maintain a stable and continuous visual output, the refresh rate must therefore be proportionally higher — the more multiplexing, the higher the required refresh rate.

Practical Impact

Full Scale Drive (1:1)
Each LED remains on continuously. Even moderate refresh rates (e.g. 1920 Hz) deliver a stable image.

1/6 Scale Drive
Each LED is only active about 16–17 % of the time. To prevent visible flicker — particularly for cameras — the refresh rate must be much higher (typically 3840 Hz or more).

In Practice

• Low refresh + high multiplex (1/6, 1920 Hz) → visible flicker, unsuitable for events, TV, or live streaming.

• High refresh + low multiplex (Full or 1/2, 3840 Hz) → crystal-clear, flicker-free image, even on camera.

• Balanced setup: 1/3 or 1/2 drive at 3840 Hz gives a good balance between price, brightness, and visual quality.

Rules of Thumb

Summary

Drive mode determines how often each LED receives current per cycle, while refresh rate determines how fast that cycle repeats. The higher the multiplexing ratio, the more critical it becomes to increase refresh rate to achieve a stable, camera-friendly image.

Bit depth is one of the less glamorous but absolutely crucial parameters for image quality in LED displays (and in any other type of display).
It defines how many steps of brightness or colour each pixel can reproduce.

Grayscale (Monochrome Bit Depth)

An LED cannot dim continuously like a traditional light source.
Instead, it uses Pulse Width Modulation (PWM) — rapidly switching on and off to simulate intermediate brightness levels.

Bit depth = number of possible brightness levels.

The higher the bit depth, the smoother the gradation between dark and bright tones.
Low bit depth results in visible “steps” or “banding” (not to be confused with refresh-related banding).

Colour (RGB Bit Depth)

Each pixel typically consists of three diodes — red, green, and blue.
Each channel (R/G/B) can represent a range of intensities.

If each channel has 8 bits, it can show 256 levels per colour:
→ 256 (R) × 256 (G) × 256 (B) = approximately 16.7 million colours — known as 24-bit colour.

Other common combinations:

• 10 bits per channel = 1,024 levels → 1.07 billion colours (HDR range)

• 12 bits per channel = 4,096 levels → 68.7 billion colours

Advantages and Disadvantages

Low Bit Depth (e.g. 8-bit grayscale)
✔ Lower cost, less processing and data bandwidth required
✘ Risk of “posterisation” — visible jumps in gradients and poor shadow detail

High Bit Depth (12–16-bit grayscale)
✔ Smooth transitions, no visible banding, better detail in both shadows and highlights
✔ Essential for video, HDR, or professional broadcast
✘ More expensive electronics, higher data rate between controller and panels
✘ Requires higher refresh rate to avoid flicker

Colour Bit Depth (RGB)

8-bit per channel remains the standard for most LED applications.
10-bit or higher per channel is required for HDR video, film production, and broadcast-level quality.

In LED Practice

Many LED controllers advertise “14–16 bit grayscale”.
That technically represents 16,000+ brightness levels — but the effective bit depth may be lower if refresh rate or driver chips cannot keep up.

So even when the specification says “16-bit”, the real visual output can resemble 12-bit.
You simply can’t maximise every parameter at once — there’s a balance between performance, data rate, and cost.

Recommended in Practice

• Outdoor advertising: 12–14 bit grayscale is more than sufficient, as sunlight and viewing distance limit the visible nuance range anyway.

• Indoor high-end events, broadcast, or cinema screens: 14–16 bit grayscale and 10–12 bit colour depth are essential to avoid banding and ensure accurate colour reproduction.

Summary

• Grayscale bit depth = how finely each pixel can dim from black to full brightness.

• Colour bit depth = how many colour shades can be created through RGB combinations.

• Higher bit depth = smoother, more realistic images — but with greater cost and processing demands.

What is a nit?

A nit equals one candela per square metre (cd/m²) — a measure of how much light a screen emits per surface area.
One candela roughly corresponds to the light intensity of a single candle observed from a distance of one metre.

The term nit originates from the Latin nitere, meaning to shine or glow.

How is it measured?

Brightness is measured using a luminance meter or a spectro-radiometer, recording cd/m² across the display surface.
Testing is typically done with a full white image (100% output).

Manufacturers usually specify peak brightness — the maximum measurable output value.

What is “enough” brightness in practice?

It depends entirely on the intended environment and application:

Rules of Thumb

• A high-end smartphone (e.g. iPhone, Galaxy) peaks around 800–1200 nits, just enough for sunlight readability with some strain.

• A quality outdoor LED display should deliver at least 5000 nits to remain visible in bright sunlight.

• Outdoor sports or events: 6000–8000 nits is sufficient.

• Iconic locations (Times Square, Piccadilly Circus): often exceed 10,000 nits for maximum daylight impact.

Pros and Cons

Too low nits:
→ The display appears faded or “washed out” in sunlight, even if technically functioning.

Too high nits:
→ Increases power consumption and LED wear.
→ Causes glare or visual discomfort at night (hence most systems include automatic dimming via light sensors).

Summary

Nits measure brightness in cd/m².
The higher the number, the better visibility under sunlight.
For direct-sunlight outdoor use, a minimum of 5000–6000 nits is required for clear, high-contrast images.

The importance of contrast

Good contrast can often compensate for lower absolute brightness (nits).
The human eye perceives image clarity based on the difference between light and dark areas, not just on raw brightness.

What is contrast ratio?

Contrast ratio = the ratio between the luminance of the brightest white and the darkest black the display can produce.

Example:
A 3000:1 contrast ratio means the white is 3000 times brighter than the black.

Practical Meaning

• High contrast: Makes images appear more vivid and “pop” even without extreme brightness.

• Low contrast: Results in greyish blacks and flat, lifeless images regardless of high nit levels.

How is contrast measured?

Typically measured with a luminance meter or a camera-based measurement system:

1. Measure brightness on a full white image (cd/m²)

2. Measure on a full black image (cd/m²)

3. Divide the two values

Testing should take place in a dark environment to avoid influence from ambient light.

For LED screens, contrast depends heavily on construction details:

• Black masks or shader fins between diodes reduce stray light

• Surface coatings improve black levels and visual depth

Good and Poor Contrast

Good contrast:
→ Deep colours, excellent legibility, enhanced 3D perception

Poor contrast:
→ Even 6000 nits looks “milky” if the black level is too high

Be cautious with spec-sheet contrast ratios — some use dynamic measurements that exaggerate the numbers beyond what’s visible in real use.

What Is “Enough” Contrast?

Interaction Between Contrast and Nits

High contrast can partly offset lower brightness levels.
For example, a 4000-nit screen with 5000:1 contrast may look better than a 6000-nit screen with only 1000:1 contrast.

However, under direct sunlight, contrast cannot replace brightness — absolute luminance remains critical.

Performance Matrix

Summary

Contrast enhances perceived depth and clarity.
High contrast reduces the need for extreme brightness indoors,
but in direct sunlight, brightness (nits) still dominates visual performance.

Banding is a temporal issue — related to timing between the LED refresh rate and a camera’s shutter.
Moiré is a geometric issue — interference between two grid patterns.

If you see horizontal dark lines, think banding/refresh problem.
If you see strange zig-zag or rainbow-like patterns, think moiré.

Banding

Banding appears as dark horizontal stripes or “rolling bars”.
It occurs when the camera’s capture frequency does not synchronise with the LED display’s refresh rate.
This mismatch causes parts of the image to be captured during the off-cycle of the PWM sequence.

Moiré

Moiré patterns are interference effects caused when two grid structures — the pixel matrix of the LED display and the pixel grid of a camera sensor — overlap at certain angles or distances.
They create visible wave-like or rainbow-coloured distortions, especially when filming fine-pitch LED displays.

Key Differences

How to Avoid It

• Banding: Choose LED systems with high refresh rates (3840 Hz or higher). These are “camera-safe” and eliminate flicker during filming or livestreaming.

• Moiré: Slightly change the camera’s position or focal distance. Alternatively, use diffusion filters or adjust the pixel pitch to avoid alignment with the camera’s sensor grid.

Summary

• Banding = refresh-related issue between screen and camera timing.

• Moiré = optical interference between two pixel grids.
  Both can distort images, but only moiré is purely visual — banding is electrical/temporal.
  High refresh and correct camera setup effectively prevent both.

This is one of the classic and most important distinctions in LED display technology, because both DIP and SMD technologies are still in use today.

What Are DIP and SMD?

DIP (Dual In-line Package)
The traditional LED design — small cylindrical diodes with two leads (anode/cathode) soldered through the circuit board.
Each pixel usually consists of three separate diodes (red, green, blue) placed side by side.

SMD (Surface Mounted Device)
Modern LEDs — where red, green, and blue chips are combined into a single small package mounted directly onto the surface of the circuit board.
Each pixel is thus a compact, integrated unit.

Advantages and Disadvantages

DIP – Advantages

• Very high brightness (up to 8,000–10,000 nits or more).

• Extremely robust for outdoor environments (heat, humidity, UV exposure).

• Lower price per nit in large-scale production.

• Long lifespan (often exceeding 100,000 hours).

DIP – Disadvantages

• Lower resolution: difficult to achieve fine pixel pitches (rare below 10 mm).

• Larger pixels = visible “dot pattern” at short viewing distances.

• Narrower viewing angle — light is projected more directly forward.

• Colour blending less precise due to physically separated R/G/B diodes.

SMD – Advantages

• Enables very small pixel pitches (down to P0.9 or less).

• Excellent colour blending because R/G/B are housed together.

• Wide viewing angle — consistent appearance from the sides.

• Ideal for indoor, semi-outdoor, and high-end applications.

SMD – Disadvantages

• Lower maximum brightness (typically up to 6,000–7,000 nits).

• More sensitive to moisture, UV, and mechanical shock — requires proper sealing outdoors.

• Higher cost per square metre at comparable brightness levels.

Where Each Is Used

DIP:
Still common in large outdoor billboards, stadium advertising, roadside screens — anywhere brightness, robustness, and cost efficiency are key, and viewing distance is long.

SMD:
Dominates indoor LED displays, semi-outdoor use, and high-end outdoor installations where resolution, colour quality, and viewing angle matter most.

Rules of Thumb

DIP = the workhorse — strong, bright, and reliable, but visually coarse.
SMD = the design choice — refined, precise, and flexible, but more delicate and costly.

“Black” – the new black?

This detail may sound small, but it’s essential: LED pixels are not only about how bright they can shine, but also about how dark they appear when turned off. The area between the bright points defines how deep and rich the image looks.

What Does “Black LED” Mean?

When manufacturers talk about black LEDs or black packages, they refer to the encapsulation material surrounding the LED chip and lens.

• Standard (white/grey package): The surface reflects more ambient light, so when the screen is off or viewed in sunlight, it can appear greyish or washed out.

• Black package: The diode casing itself is dark. This reduces reflections and increases perceived contrast — blacks appear deeper, whites seem brighter by comparison.

Advantages of Black LEDs

• Higher perceived contrast and improved depth.

• More vivid colour reproduction, especially in dim or indoor environments.

• Visually superior image quality for premium installations or event use.

Disadvantages

• Slightly lower absolute brightness: the darker casing absorbs light instead of reflecting it outward (typically 10–20 % loss).

• Higher production cost.

• The dark surface can absorb more heat from sunlight, posing thermal challenges in outdoor setups.

When Are Black Packages Worth It?

• Indoor high-end installations: excellent choice where contrast and colour richness matter more than maximum brightness.

• Outdoor billboards in strong sunlight: usually less beneficial — brightness (nits) matters far more than fine contrast.

3535 vs 2727 Packages

The numbers describe package size in millimetres:

3535: larger LED, used mainly for outdoor screens where maximum brightness and robustness are required.
2727: smaller LED, used for closer-pitch displays (P3.9, P4.8, etc.), providing better contrast and finer image detail.

Summary

• Black LEDs = better contrast, richer colour, slightly lower brightness.

• 3535 = bright, tough, outdoor-oriented.

• 2727 = smaller, higher resolution, ideal for indoor / semi-outdoor use.

• Combine 2727 + black package for stunning image quality and contrast — but not the brightest output.

Rule of thumb:

• Direct sunlight outdoor → 3535 white package (max nits, robustness wins).

• Indoor events / premium displays → 2727 black package (superior contrast, fine detail).

• Semi-outdoor / urban spaces → 2727 white (balanced brightness + contrast).

Now we’re getting down to the LED chip level — how diodes are physically designed and electrically connected.

“Negative cathode technology” (often called common cathode or common anode, depending on circuit direction) describes how the three colour chips in each LED share electrical connections.

How It Works

Each RGB LED contains three chips — red, green, and blue — each with its own anode (positive) and cathode (negative).

• Common Cathode (shared negative):
  All three colour chips share a single cathode connection (–), while each colour has its own individual anode (+).
  → Current flows into each colour line and out through the shared negative.

• Common Anode (shared positive):
  All three chips share one anode (+), while each has a separate cathode (–).
  → Current flows in through the same point and exits individually.

Advantages of Common Cathode

• Lower heat generation – each colour channel can be powered with precisely the voltage it needs (red, green, and blue require different forward voltages).

• Reduced energy loss – less unnecessary voltage across chips means less wasted power.
  → Typically 10–20 % lower power consumption compared with common anode.

• Improved colour stability – lower heat reduces “thermal drift” (e.g. blue diodes shifting towards green under stress).

• Longer lifespan – less heat stress on the LED package and materials.

Disadvantages

• More complex driver electronics – each colour needs separate voltage control, increasing circuit complexity.

• Higher design cost – requires advanced driver ICs and more precise power distribution.

• Compatibility issues – not all LED controllers or modules support common cathode layouts, as common anode remains widespread.

• Smaller benefit in high-brightness outdoor setups – when all colours run at near-max voltage, the efficiency gain is limited.

When It’s Useful

Common cathode is ideal for:

• Indoor or semi-outdoor displays where colour quality, low heat, and long life are priorities.

• High-end events, broadcast, control rooms, or applications demanding consistent colour performance.

Less relevant for:

• Large outdoor billboards prioritising maximum brightness and lowest cost.

Simple Analogy (The “Garden Hose” Example)

• Common Anode: One shared water tap (+) feeds all hoses; each hose drains separately (–).

• Common Cathode: Each hose (colour) has its own tap (+) but drains into one shared outlet (–).

Common cathode gives better control and efficiency — but requires more taps (electronics).

Summary

• Common cathode = lower heat, lower power use, improved colour stability, longer lifespan.

• Disadvantages: higher component cost, more complex control, less standardised.

• Best suited for high-end indoor or semi-outdoor LED systems where image precision outweighs raw brightness.

LEDs don’t usually “die” suddenly. Instead, they gradually lose brightness over time — a natural ageing process.
Lifespan is typically expressed as L70 or L50:

• L70 = when light output has dropped to 70% of its original value

• L50 = when it has dropped to 50%

For modern LEDs, L70 is often between 50,000–100,000 hours of operation, assuming correct thermal management and drive current.

Load and Brightness

When an LED runs at 100% drive current, it generates significant heat.
Excess heat accelerates chemical degradation in the chip, phosphor, and encapsulation materials.

If you instead run LEDs at 80–90% drive current, several things happen:

• Heat generation drops sharply

• Material breakdown slows down, extending service life dramatically

• Brightness loss over time is reduced, and colour stability improves

Typical Results from Manufacturers

• An LED wall running at 100% output might reach L70 at ~50,000 hours.

• The same wall, driven at 90%, can often achieve 70,000–80,000 hours before L70.

• In practice, a 10% brightness reduction can extend lifetime by 30–60%, while the perceived visual difference is minimal.

Other Benefits of Running Below Maximum Power

• Reduced colour drift – less thermal stress means colours remain consistent over years.

• Lower power consumption – direct energy savings and less load on power supplies.

• Improved uniformity – slower degradation keeps pixel brightness more consistent across panels.

Practical Conclusion

For outdoor displays in direct sunlight, it’s tempting to run LEDs at full power all the time.
But by designing systems with extra headroom (e.g. 7,000–10,000 nits capability) and operating them at 5,000–6,000 nits daily,
you achieve the same visual effect while greatly extending lifespan and reducing maintenance cost.

This is why premium LED suppliers overspecify their brightness capacity but limit actual operation to about 80–90%.

Summary

• LEDs degrade gradually; not through failure but through reduced luminance.

• Running at 80–90% greatly increases lifespan and colour stability.

• Smart operation = less heat, longer life, better image consistency.

In practice, power supplies (PSUs) are often the weakest link in an LED display system.
While the LEDs themselves can last 50,000–100,000 hours if driven properly, the PSUs typically have a shorter lifespan.

Why PSUs Wear Out Faster

1. Heat

   • Capacitors — especially electrolytic types — age rapidly when exposed to high temperature.

   • Rule of thumb: for every 10°C increase above design temperature, lifespan is halved.

2. High load operation

   • Many PSUs run close to 80–100% of their rated capacity inside LED cabinets.

   • Continuous high load accelerates wear and heat buildup.

3. Environmental stress

   • Outdoor enclosures experience large temperature and humidity fluctuations.

   • Condensation and corrosion can occur even with ventilation or air-conditioning systems.

4. Power quality

   • Voltage spikes and unstable mains power increase component stress and shorten lifespan.

What to Consider When Designing a System

1. Proper Dimensioning

• Always include headroom:
  If the display requires 800 W, choose PSUs rated for 1,200 W total.

2. Temperature Management

• Ensure good ventilation and thermal design.

• Monitor internal temperatures — not just LED panel temp, but also inside the PSU compartment.

3. Quality Components

• Cheap, unbranded PSUs may last only 10,000–20,000 hours.

• Reputable brands such as Mean Well, Delta, or TDK-Lambda can achieve >100,000 hours at 50% load.

4. Modular Service Design

• Displays should allow quick PSU replacement.

• Planned maintenance cycles (typically every 5–7 years) reduce unplanned downtime.

5. Monitoring and Predictive Maintenance

• Smart PSUs or controllers can report voltage, current, and temperature.

• Replace proactively before total failure — e.g. when 5% or more of PSUs show degraded performance.

Example: Cost and Lifetime Calculation

Scenario:
Outdoor screen with 12 PSUs, operating 24/7 for 5 years.
Unit cost: 900 DKK per PSU, labour cost: 600 DKK per replacement.

Conclusion:
Operating PSUs at 70–85% load can reduce PSU-related costs by 30–50% over a 5-year period – and significantly reduce system downtime.

Summary

• PSUs typically wear out before the LEDs.

• Use quality units with load headroom and thermal control.

• Plan for periodic replacement every 5–7 years.

• Heat is the primary enemy — small reductions in load or temperature dramatically extend lifespan.

What is the difference between COB and GOB LED technology?

COB (Chip On Board) and GOB (Glue On Board) are often mentioned together, but they serve very different purposes.

What is COB?

COB is a chip packaging technology where LED chips are mounted directly onto a shared PCB or ceramic substrate and covered with a phosphor and protective layer.

COB advantages

• Very dense pixel pitch (typically 0.6–1.2 mm)

• Homogeneous, matte surface

• Excellent heat dissipation

• High brightness and strong contrast

• Reduced moiré and better camera performance

COB is primarily used in high-end indoor displays, such as broadcast studios, control rooms, and premium corporate environments.

COB itself is not waterproof, but it is more resistant to dust, touch, and ESD than traditional SMD.

What is GOB?

GOB is a protective coating, not a display technology.
A transparent epoxy or silicone gel is applied over the LED surface (SMD or COB).

GOB advantages

• Water-resistant and shock-resistant surface

• Easy to clean

• Ideal for public spaces and rental use

GOB is commonly used in outdoor, semi-outdoor, and high-traffic environments, where durability and IP rating are critical.

With GOB, front-side IP ratings of IP65 or higher can be achieved.

Does GOB improve image quality?

No.
GOB improves robustness and protection, not image quality.

In fact, all protective layers absorb and scatter light:

• COB typically reduces light output by ~5–10%

• GOB can reduce light output by ~8–20%

This is why GOB displays often require higher brightness and power consumption to compensate.

Can COB and GOB be combined?

Yes.

A fine-pitch COB display with a thin, matte GOB coating combines:

• Excellent image quality

• High durability

• Improved IP protection

This results in a very robust but heavier and more expensive system, often used where both visual performance and physical protection are required.

Quick rule of thumb

• Broadcast, control rooms, near-field viewing → COB

• Public spaces, rental, outdoor → GOB

• One solution for everything → COB + thin matte GOB

Black Striping – White Striping

This term describes visible lines that appear when LED cabinets are not perfectly aligned during installation.

• If there is a small physical gap between cabinets — even as little as 0.1 mm — you may see black stripes where no LEDs are emitting light.

• If cabinets are slightly pushed together or bent inward, the adjoining rows of LEDs can overlap visually, producing brighter white lines (white striping).

In short:
Precision alignment and mechanical tolerance are crucial to avoid visible seams or brightness inconsistencies across panels.

Redundancy

In LED systems, redundancy means dual signal or power cabling.
If one line fails, the secondary line automatically takes over.

The audience will not notice the change, but if the system is monitored, the service technician receives a fault alert and can fix it at the next scheduled maintenance.

Purpose:
To increase system reliability and reduce downtime in mission-critical applications such as events, airports, and digital signage networks.

ABC – Automatic Brightness Control

ABC (Automatic Brightness Control) refers to the light-sensor system that adjusts screen brightness according to ambient light.

• During daylight, it raises the brightness for visibility.

• At night, it automatically dims to as low as 0.1% of full output.

A well-designed ABC system ensures:

• Comfortable viewing at all times,

• Reduced power consumption, and

• Extended LED lifespan through lower night-time operation.

Note: even 1% brightness can be excessive in certain dark conditions —
top-tier systems adjust smoothly across an ultra-wide dynamic range.

Summary

• Black/White Striping: Caused by mechanical misalignment between LED cabinets.

• Redundancy: Dual-line power or signal backup to prevent visible failures.

• ABC: Automatic brightness adjustment for efficiency and comfort — vital for modern outdoor LED screens.