Light emitting diodes (LEDs) are special diodes containing a specific chemical compound on a microscopic wafer that emits light when subjected to an electrical current. The emission of light depends on electrons flowing through the anode and cathode within an LED chip, and the color of the visual emission depends on the materials utilized. The most important part of a light-emitting diode (LED) is the semiconductor chip located in the center of the bulb. The chip is formed by bringing two slightly different materials together to form a PN junction. In a PN junction, the P side contains excess positive charge (“holes”, indicating the absence of electrons) while the N side contains excess negative charge (electrons). When a forward voltage is applied to the semiconductor element forming the PN junction, electrons move from the N area toward to P area and holes move toward the N area. Near the junction, the electrons and holes combine. As this occurs, energy is released in the form of light that is emitted by the LED. The junction acts as a barrier to the flow of electrons between the P and the N regions. Only when sufficient voltage is applied to the semiconductor chip, can the current flow and the electrons cross the junction into the P region.

The material used in the semiconducting elements of a LED determines its color. The two main types of LEDs presently used for display systems are aluminum gallium indium phosphide (AlGaInP, sometimes rearranged as AlInGaP) alloys for red, orange, and yellow LEDs; and indium gallium nitride (InGaN) alloys for green and blue LEDs. Slight changes in the composition of these alloys change the color of the emitted light.

Individual LEDs are low-voltage devices. Normally Single LEDs require 2.5 to 4.5 volts of direct current, which current in the range from 1 to 100 milliamperes. LEDs require a specific electrical polarity. Applying voltage in reverse polarity can destroy them. Manufacturers provide specifications about the maximum reverse voltages acceptable for LED devices; 5 volts is a typical maximum rating.

The below graph is the typical LED electrical characteristic.

There are various applications utilizing LEDs. If we are talking about the LEDs used for full color video display, the light ranges from 40mcd to 1600mcd depending on different packaging and different color.

LED displays are made of two main type of LED lamp structure: the trough-hole LED (also called conventional or lead-type LED) and the surface-mount LED (also called SMD LED).

The through-hole LED is the most common type of LED package. It is connected to the circuit board via its leads that also serve as the interface to the power source. The through-hole LED is not surface mountable.

The surface-mount LED has been designed to conform to the requirements of the surface mount circuit- board manufacturing environment. Surface mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto printed circuit boards (PCBs) surface PCBs). Electronic devices so made are called surface-mount devices or SMDs.

Through-hole LED

Surface-mount LED

Surface-mount LEDs are increasingly popular and are now found in indoor as well as indoor/outdoor LED display applications.

Around 2000, the surface-mount LED became bright enough to use for indoor display applications ons. The surface-mount, three-in-one technology permitted LEDs to be spaced closer together on a display face, allowing displays with a pixel pitch as tight as 3 millimeters to be manufactured. It also allows for wider viewing angles, gave better evenness to the display picture, and improved display color and consistency as explained in the drawing below.

In the manufacturing of semiconductor products, there is a variation in performance around the average values given in the technical data sheets. Like snowflakes, no two LEDs are alike. There are variations in color (wavelength), brightness (flux), forward voltage (Vf), and beam distribution/artifacts. These variations are due to differences in raw material sources, crystal growth, handling, storage conditions for the raw materials, and basically all of the other variables that go into a manufacturing process.

For this reason, most LED manufacturers bin (= sort by machine into bins) the LED components for flux, color, and forward voltage (Vf). Each bin has a rank or window of values that all the parts in that bin fit within. In spite of the fact that only some of the variables are binned and the bins are fairly wide there can be quite a few bins. From one extreme to another, a typical LED from the same production line can have a 300% variation in one value alone.

A major factor in the appearance of an LED display is consistency in the brightness of the LEDs across the face of the sign. The impact of variations in brightness is critical in multicolor LED signs where red, green, and blue are mixed to produce full-color displays. As the LEDs are energized at different ratios to produce the desired color, variations inherent in the sign hardware and the LEDs themselves can result in distortions of the desired hue.

There are generally small differences in color among LEDs when they are first produced, and then drift in color as they are operated over the long term. Without carefully designed compensation circuits to account for the different rates of brightness and color for the video display, the appearance of the display can be fleck or dither. LED Manufacturers work to bin LEDs to provide batches of products that will have similar initial appearance. For full color LED video display, binning is not enough for true color reproduction.

Below graph shows the color area of a bin.

Because LEDs are solid-state devices that control current without heated filaments, they are very reliable when operated within design parameters. Usually, LEDs are designed to operate upwards of 100,000 hours.

The most common way for LEDs to fail is the gradual lowering of light output and loss of efficiency. In practice, the standard method used to express the life of a LED is the time it takes to reach 50% of its day one brightness. LEDs fade at a significantly faster rate after half brightness. The typical lifetime of LEDs used in artixium outdoor displays usually ranges around 100,000 hours.

The 2 following remarks are important to note:

• Red/Green/Blue LEDs have a different decay curve (see chart above) which implies that the color uniformity of a LED display cannot be guaranteed over time without human intervention;
• The degradation of LEDs is accelerated by heat, high current density, and emitted light which implies that operational actions may be taken to extend the lifetime of the display.

Next to the gradual lowering of light output, LEDs can also undergo sudden failures. Sudden failures are most often caused by thermal stresses. When the epoxy resin used in packaging reaches its glass transition temperature, it starts rapidly expanding, causing mechanical stresses on the semiconductor and the bonded contact, weakening it or even tearing it off. Conversely, very low temperatures can cause cracking of the packaging.

In general, the cooler the environment, the higher an LEDs light output will be. Higher temperatures generally reduce light output. In warmer environments and at higher currents, the temperature of the semi-conducting element increases. The light output of and LED for a constant current varies as a function of its junction temperature. The temperature dependence is much less for InGaN LEDs (e.g. blue, green, white) than for AlGaInP LEDs (e.g. red and yellow).

Most LED manufacturers publish curves similar to this graph for their product. It is interesting to see that for this 3-in-1 SMD product’s blue become brighter when the ambient temperature increased.

However, prolonged heat can significantly shorten the useful life of many LED systems. Higher ambient temperature leads to higher junction temperatures, which can increase the degradation rate of the LED junction element, possibly causing the light output of and LED to irreversibly decrease over the long term at a faster rate than at lower temperature. Controlling the temperature of an LED is, therefore, one of the most important aspects of optimum performance of LED systems.

No, the maintenance of brightness depends on several factors :

• Different bins – Each LED from the same manufacturer may have different brightness characteristics and maintain differently over time.
• Different Operating Conditions – The operating conditions such as ambient temperature or current through the LED will influence the brightness output over time. Higher ambient temperature can cause the light output of an LED to decrease over the long term at a faster rate than at a lower temperature.
• Different behavior for R/G/B LED – Different semiconductor materials will have different degradation properties; additionally, short-wavelength light will tend to cause more degradation in epoxy materials used to encapsulate the junction element.
• Different places in the system – The performance of a single LED in a system is strongly influenced by its position in the entire system. For example, LEDs near the fan might experience lower overall temperatures and therefore experience slower reductions in performance than LEDs near the power supply units.

The main reasons that LEDs are suitable for full-color video display applications are :

• Today, LED technology is the technology of choice to display a good image under any light condition, even in direct sunlight. LED is therefore widely used in outdoor environments or at auto shows where there is plenty of ambient light.
• LED display is the ideal choice for a large, seamless display wall.
• LED is more rugged and has a longer lifetime than other display technology. LED technology is by nature very stable, demonstrating a long lifetime and reliability: Even for operation 24 hours a day, the displays last for many years with little maintenance.
• LED technology provides a much wider color gamut (providing more accurate color fidelity).
• Assembling an LED display is simply a result of linking smaller modules together. This modular system makes LED displays suitable for any type of installation (walls, roofs, temporary structures for specific events, etc.), enables easy maintenance and does not set any limits in shape, size, and resolution.

At 6500oK we have ~63% RED, ~100% GREEN and 55% BLUE.

This is an important impact on the measuring of the maximum brightness of the display. To achieve maximum brightness (all LEDs 100%) one can’t show pure white anymore. That is why a color-calibrated wall at pure white is the only valid reference for brightness measurement.

The LED manufacturer is Nichia. All the remaining information is proprietary to artixium and is only available after the customer signs a non-disclosure agreement with artixium.

This table gives you an idea of what a potential client would be looking for. The yellow zones
remain confidential information from our side.

A frequently asked question probing into continuity, and servicing. artixium fully designs, and manufactures all elements of mechanics, electronics driver boards, processing boards, digitizers, and software enabling artixium to control and steer every link of the chain for optimal picture performance, minimum power consumption, and ultimate reliability.

This fact in addition to the worldwide support structure of artixium clearly differentiates us from 95% of the competition.

artixium’s “no compromise” product development towards image quality has led to a very dense number of LEDs/m2 compared to similar competing products. This has as result to increase the fill factor (the area of the display actually covered by LED components) for a smoother picture.

Brightness

At 6500K, measured on 1 tile we obtain the following light output:

HYDROGEN, 6500 nits

It is important to specify the color temperature at which this measurement is being done, as there are many ways to measure the brightness of an LED display and each leads to very different results:

• At full drive (all LED at 100% driven). This means no stable color is achieved as the measure is done.
• At any white point, which means taking one white point on the display we measure its output. This also has no real value for the display as a whole.
• At tile level, taking one uniform tile performing full white at 6500K we measure its output, Individual LED correction white light output. (artixium = 8000nit)
• At wall level, calibrated white light output level. (artixium = 6500 nit)

Obviously, the measure of the brightness decrease as we refine the measuring technique (from 1 to 4) to give a reference, from technique 3 to technique 4 as much as 18% brightness will be lost, if artixium makes its measurements at wall level.

Viewing Angle

The optimal viewing angle of the artixium display is inside 140o. This does not mean that no picture will be visible outside this angle coverage. Outside that range, less than 50% of the nominal brightness will be perceived by the viewer. A picture will still be seen, just less bright.

An important concept when evaluating view angles is the color shift effect. Because of a slight difference in the shape of the lenses fitted on top of the LED components, a white picture would look quite white when looked dean-on but would turn greenish or yellowish when looked at from an angle. The shader shape  will also affect the color shift under some certain conditions. artixium’s stringent selection of its LED components and special shader geometric design enables it to reduce that color shift effect to near zero.

The contrast ratio is calculated by the formula :

Contrast ratio = (maximum brightness – minimum brightness)/minimum brightness.

Artixium accumulated lots of know how to improve the contrast ratio. The latest improvement incorporates a new “light trap” shader. Its new geometric design combined with special selected dark black, matt materials essentially “trap” the light falling on the display ensuring superb black levels. When combined with the high brightness output, it could deliver vastly improved contrast levels to its predecessor.

Color processing bit or grey-scale bit is the basis for determining the overall color capability of an LED video display. We take RED as example, if the color depth is 10 bit, there will be total 1,024 shades of red.

Generally speaking, the higher the color processing bit rate, the better the picture quality is. It is known the pixel of a LED display is composed by at least 1R/1G/1B. The pixel then could display various colors by different percentages of red, green and blue.

The left picture is 4 bit and the right picture is 8 bit.

All artixium outdoor displays are equipped with shaders. These shaders have been selected for their unique specifications. These are made of carefully selected matt materials and are water repulsive (to avoid magnifying effect of water droplets on the display), non flammable (security in public spaces, sports stadium) and UV resistance (long term outdoor exposure).

The image on a large outdoor LED display is visible from a long viewing distance. However, the closer the observer gets to the display, the more unpleasant and uncomfortable the viewing of a picture will be. To best determine the pixel pitch required for a given LED display, a minimum viewing distance must be defined.

Minimum viewing distance based on the theory of visual acuity :

This minimum estimated viewing distance is based on the visual acuity that is normally taken to be approximately 1 minute of arc (1/60th of a degree) for a typical viewer with 20/20 vision. Technically speaking, visual acuity is a measure of the eye’s spatial resolving power and indicates the angular size of the smallest detail that the human visual system can resolve. For example, if two thin, bright parallel lines are viewed on a dark background, the visual acuity of the eye will define how close together the lines can be before the eye sees them as a single bright line rather than two separate lines. This is defined in terms of angle rather than distance because the distance between the lines in inches (or millimeters) will depend on how far away they are: if they are 1 mm apart, the lines can easily be separated at a distance of 15 cm, but probably not at a distance of 10 m. This is relevant to LED displays because if the separation between pixels exceeds this angle, the observer will be able to make out the individual pixels as pixels rather than simply seeing a smooth image. If the pixel separation is significantly smaller than this angle, the typical eye cannot actually resolve any more detail, so the extra resolution is wasted. Based on this 1 minute of arc angle, a list of minimum viewing distances for various pixel pitches can be easily compiled by multiplying the pitch by approximately 3400. For example, a 10-mm pitch results in a minimal viewing distance of 34 m.

Other way of calculating viewing distances :

In reality, this minimum calculated viewing distance, based on the theory of visual acuity, is a very (very) conservative estimation of a “minimum viewing distance.” It could, in fact, be divided by 3 or 4 while still being acceptable as viewing distance. As the observer comes closer to the display, the pixelisation will not be bothersome – personal preference plays a big role in defining what each viewer perceives as being the minimum viewing distance. Below, a chart calculating a minimum viewing distance being the point at which the fully illuminated red, green, and blue components appear to the eye to blend into white. While the maximum Distance is the point at which the smallest characters the display can generate begin to be illegible (This point varies greatly with the content of the display). In this case, you will notice that the viewing distance and much less conservative than the ones expressed by the theory of visual acuity.

As a rule of thumb you can use

• 4mm equals with 4m viewing distance
• 6mm equals with 6m viewing distance
• 10mm equals with 10m viewing distance
• 20mm equals with 20m viewing distance

In order to have the visual impression of a computer display at 1/2 meter, a display of 7.2mx5.5m is required at 100 m – and a display of 6mx4.5m is required at a distance of 60 meters.

To make sure that the display we are placing will not look like a stamp at the end of a stadium. Take a picture of the location, measure its scale, draw a mock-up of the display to scale, evaluate visual impact.

Regarding the recommendation of the pitch, we need to consider the following items:

1. Viewing distance
2. Display size
3. Desired content (video or text)
4. Traffic speed

The 2 first points has been discussed previously. Below a chart to illustrate point (3) and (4).

The pixel pitch is a defining factor of a large LED display because the closer the pixels, the closer the minimum viewing distance can be in order for the image to appear smooth. Accordingly, as the distance between pixels decreases, the cost of the screen per square area increases. Therefore, the pitch determines both the image definition and cost of the screen. A small pixel pitch results in higher resolution and cost; a large pixel pitch results in lower resolution and cost.

Clients who intend to purchase LED displays tend to opt for a smaller pixel pitch and, therefore, a higher image quality. However, this must be carefully investigated. The visible area of a LED screen has two dimensions, which mean that the cost increase will follow a square law when reducing the pixel pitch.

For example, reducing the pitch by 30% increases the number of pixels by 100%, and cost follows.

For example, if the pixel pitch is reduced by 20%, from 20 to 16 mm, the pixel count will increase by more than 50%, from 2500 pixels (50 × 50 = 2500) for 20 mm to 3844 pixels (62 × 62 = 3844) for 16 mm.

It is therefore important to balance the cost factor with the required display resolution for good perceived image quality. In fact, the human eye is not able to recognize small details from long distances. So, the designer should always question the need for a higher resolution LED screen if the observers will not be able to appreciate its superior visual performance.

The artixium displays are adjustable in steps such as 3200K, 5400K, 6500K, 7000K, 9500K.

The color temperature of a light source is determined by comparing its hue with a theoretical, heated black-body radiator. It is marked as a line in above CIE (1931) xy chromaticity diagram. 6500K is widely used to simulate the midday sun in Western/Northern Europe.

The color uniformity is approximately 99% (+/- 1%).

Each individual LED within each pixel has its color characteristics and brightness measured at the artixium factory once it is installed on a module. The information obtained in this process is stored on an EEPROM. At that time, each LED has individual color and brightness corrections to ensure you have a uniform image.

artixium display always has the best color reproduction which results in the best picture quality. These are the know-how’s that artixium accumulated over many years.

There are generally small differences in color among LEDs when they are first produced, and then drift in color as they are operated over the long term. Without carefully designed compensation circuits to account for the different rates of brightness and color for the video display, the appearance of the display can be fleck or dither.

LED Manufacturers work to bin LEDs to provide batches of products that will have similar initial appearance. For full color LED video display, binning is not enough for true color reproduction. artixium does a color calibration to calibrate the display pixel by pixel.

Below graph shows the color area of a bin.

There are lots of components in a LED display system. We have explained the life-time of a LED in chapter “What’s the lifetime of LEDs”.

The display system’s other components such as power supply units, fans, CCDs also have the possibilities to fail. It is more practical to adopt MTBF (mean time before fail) for those components. Normally we use LED’s lifetime as the display’s lifetime because it is the most important components of a LED display system.

We have the following recommendations to extend LEDs life time :

1. Degradation of LEDs is accelerated by emitted light. You will extend the lifetime of your LEDs by dimming the display at the minimum brightness required for the application; or even switch off the display if its operation is not required. Additionally, AEC is also an option to control the light output of the display according to environmental condition.
2. Degradation of LEDs is accelerated by heat. Do not “Drive” an LED “hard” in high ambient temperatures as it may result in overheating of the LED package, eventually leading to device failure. You may decide to switch off your display when the operating temperature is above its recommended operational range.
3. Red/Blue/Green LEDs have a different decay curve which implies that color uniformity of a LED display cannot be guaranteed over time without human intervention. Recalibration of old display may be required to improve perceived uniformity of your display.
4. Enhance the contrast of your display by washing your shaders or replacing the shaders.

It is tested under full white (@6.500°K). It is the only comparable figure of power consumption because it is clearly defined with the restrictions.

Power consumption with video or static content – To specify the power consumption with video or static content, we need know how much area of white and black of a video/static content. This is flexible for different sources. It is always estimated that the power consumption of video content is 25% of full white. It is also defined as the average power consumption. For static picture, it is estimated to 40% of full white.

Daily power consumption – To specify the daily power consumption, we need know its working conditions. Running hours, brightness settings, environment controllers are the factors to determine the daily power consumption. By utilizing the ambient environment controller, the display’s light output is optimized and changed time by time to its best suitable output.

50% brightness of the initial value.  

The LED components are the main limitation in the lifetime a display, as they are the only consumable parts of the display. The lifetime of these LEDs (time after which they will reach half brightness) is 50,000 hours if showing constant full white. However, temperature is an important parameter in the lifetime expectation. This is why extensive temperature monitoring features have been included in the tile itself, and the control software.

The MTBF figure is measured according to the MIL handbook 217E specification and has been
confirmed by extensive testing and laboratory reliability analysis.

The outdoor viewing audience is mostly mobile. Mobility limits the potential viewing time of an outdoor message to only a few seconds. There are principles for designer to create good content:

Be simple!

Too many elements may confuse a viewer or make them work to hard to understand the meaning of the message.

Be colorful!

Choose colors with high contrast in both hue and value. Avoid using a white background. Below 11 color combinations are ideal for outdoor LED content design.

Be bold!

Use large and legible typefaces. Choose fonts that are easily read at long distances. Fonts with thin strokes or ornate script will be difficult to read.

Pixel to pixel

Create the files at double pixel resolution of your display.

Compression : try to avoid it. It is a tradeoff between quality and file size.

NB: do not forget to use a high quality signal (e.g. DVI) instead of a low quality one (e.g. VGA)

The minimum screen refresh rate is 800Hz, to obtain an ultimate flicker free image.

Special displays even enhance its refresh rate > 3000Hz, to obtain an ultimate flicker free image under professional camera. It is optimal as an ideal solution for broadcast application.

On signal input side, as of today, artiXium can offer compatibility to HDTV standards through their standard display controller and usage of an external video scaler. As learned the best picture quality is obtained addressing each pixel by pixel, means the pixel resolution of the whole LED display should have HDTV resolution.

Yes! artixium offers as an Ambient Environment Controller option for fixed installations to achieve optimal brightness/contrast in all weather conditions.

All artixium products are designed for optimal flexibility and easy serviceability. The modules are small in size, light, and easy to carry. The very restricted depth of the display enables installation in the most demanding location. The built-in intelligence enables “Plug & Play” installation, and “Hot Swap” maintenance procedure, without interrupting the performance of the display.

Most of artixium outdoor cabinets are self-contained and fully IP65 compliant. No additional actions need to be taken to handle extreme moisture or dust conditions. This particularly enables quick and reliable installation of the display outdoor, without requiring extra housing.

The CE Marking is a symbol that indicates a product complies with the "essential requirements" of the European laws or directives (directives are the mechanism by which European-wide legislation is enacted). It indicates conformity to the legal requirements of the European Union (EU) Directive with respect to safety, health, environment, and consumer protection. The CE Markings Directive (93/68EEC) was adopted on 07-22-1993. The CE-Directive gives a detailed description of the initials "CE" and the ways that conformity may be acquired. All products offered for sale within the entire EU must have the mark or they cannot be sold. The CE mark provides a visible declaration by the manufacturer that the product complies with all applicable Directives (there may be more than one applicable Directive). The conformity of the product may be proven by the following testing and/or certification procedure as outlined in the directive technical requirements The mark is affixed to the product/packaging/manuals by the manufacturer after demonstrating compliance.

Artixium "low cost" competitors (= Asian/Chinese manufacturers or US/EU manufacturers
sourcing in China) are achieving lower prices by using (by order of importance):
1. Low-quality LED lamps
2. Low-quality Power Supply
3. Low quality of other components (fans, electronic components..)
4. Lack of certifications (CE, UL)
On the artixium side, we believe that lower-quality components are not the right way forward. We
look at a Total Cost of Ownership (TCO) and target an acceptable purchase price but
with higher quality in mind. Artixium entirely designs, manufactures all elements of mechanics,
electronics driver boards, processing boards, digitizer, software enabling artixium to control
and steer every link of the chain for optimal picture performance, minimum power
consumption and ultimate reliability.
On top of the intrinsic quality of its equipment, artixium has the following added value:
• Chinese company with European management = reliability for the customer
• Artixium has a strong balance-sheet = long-term partner
• Artixium has worldwide support

Contrary to what some may think, making a "specific" product for static images does not result in huge cost savings. The explanation is simple. Around 40 to 70% (this % depends on the pitch) of a LED billboard price is coming from the small "LED lamps" (i.e. the actual lamps you see on the billboard). If you want to do static, you will in fact use the same "LED lamps" as for "video" (there is in fact no difference in the LED lamp between static / video as in both cases, the LED lamp is simply required to emit the right amount of light when subjected to an electrical current). Having said that, some cost savings could be made on the driving electronics (electronics behind the LEDs) but this will be rather minimal. As cost saving is rather minimal it will need to be balanced against customer requirements (does the customer want to take away this feature for a small saving) and other factors.

Evaluating the performance of a LED display can only be down after effectively seeing the display in action. The critical criteria to be tested comprise:

• Show pure white

• Show pure black

• Show pure Red/Green/Blue

• Evaluate different color temperatures

• Show grayscales

• Test brightness on a calibrated wall and not just at full power

• Test brightness adjustment levels

• Look at a uniform white picture form various angles, evaluate color shift 

• Perform a smooth dimming of the display, and evaluate effects on the quality of the picture in the process

• Monitor grayscale evolution in the previous dimming test

• Evaluate uniformity of picture (uniform primary colors for example, look for patches)

• Seamless picture performance (physical visibility of the tiles)

• Subjectively evaluate video performance

• Evaluate pixelisation effect from various viewing distances

• Show dark scenes

• Ask for gamma correction adjustment (both in video and data sources)

• Detect green noise in low black levels

• Detect black clipping and disappearance of details in black

• Detect solarisation effects in what should normally be smooth grayscales

• Measure power consumption

• Simulate breakdown and maintenance procedure