The Led display wall has proven to be a very effective way to transmit messages or entertainment to large groups of people. But, how?, what strengths and key advantages have Led technology against other methods of producing images of great dimensions?, what are their characteristics? In this Tribune written by Marcos Fernández, director of Christie for Spain and Portugal, for Digital AV Magazine it responds to these questions.
The operation of the Led is based on the phenomenon of electroluminescence. To move through a semiconductor, electrons shift to a State of lower quantum energy, a process in which emit photons of a specific wavelength. In general, the construction of an accurate Led a lens that allows the resulting light is issued in an efficient way in a certain direction.
For each pixel, the display wall used individual Led three colours: red, green and blue. The Led can consist of separate devices or combined in a single device for surface mounting (SMD). Each of the Led colors, known as subpixels, receives its own signal transmission based on the content of the video, allowing the generation of millions of colors.
It is normal that each tile is made up of a series of identical Led modules. Circuit modules plates are electrically connected so that each pixel receives signals transmission led RGB only and specifically to them, and to get power to the power supply of the mosaic pixels all. This modularity is an advantage during the tasks of maintenance and repair, as if an Led fails only will have to replace the module that contains it.
It is normal that all modules of a mosaic is staying in a small box which also houses the electrical supply of the mosaic, as well as the electronics necessary to control every module and permit connection of the video signal. Some mosaics are designed so that the power supply and the control electronics are located in a box, attached to a structure that contains also the Led modules.
Configuration of mosaics to suspend them from an external structure, enabling the creation of arrays with one larger number of mosaics. One or more control units separate, connected to a number of mosaics, accept video signals from a range of possible sources, typically DVI or HDMI, addressing each tile fragments of images correct.
The mechanical design of the mosaics ensures that each tile aligns precisely with the adjacent tiles. The result is a perfectly homogeneous, composed image which can be formed by thousands or millions of pixels depending on the amount of mosaics employed or the number of pixels containing each tile.
But a wall of Led display is more than a simple Led mosaics. It is normal that you required a series of external control units, each one of them in charge of a subset of the wall mosaics. Each control unit accepts signals from source devices and provides different from each subgroup of mosaics video material. Most of the solutions incorporate a video processor and Routing switches universal, as well as collaboration and content management systems.
Strengths and key advantages
As a light source, the Led present a series of advantages to consider. Firstly, the brightness. Currently, although models for interiors is not usually reach the 2,000 nits, Interior Led display walls can reach a maximum of brightness of 12,000 nits (cd/m2). And if that high gloss is absolutely essential in displays located outdoors, where they must compete against direct exposure to sunlight, is also useful in displays of interior spaces that need attention in very crowded environments.
Other methods of creating large images are incapable of reaching levels of image brightness comparable to the one of the walls of Led display or succeed only to base considerably increase the complexity of the system.
For example, LCD panels tend to achieve less than 1,500 nits brightness, with most falling below 700 nits. In the displays of projection, where the brightness of the image is almost arbitrary, depending on the size of the image with specific lamps or other light sources, it is only feasible to achieve levels of brightness comparable to the one of the walls of Led display with specific combinations of lamp and size of image by using several projectors.
The capacity of the walls of Led display to support high levels of ambient lighting is another strong point of this technology, not only the high level of brightness characteristic of the Led tiles, but also from the high contrast ratios.
The result is a remarkable level of perception of the black which has the effect of a sharp contrast in the image, no matter how elevated are the levels of ambient lighting of the interior space.
An additional strength of walls of Led display is the possibility offered to a spectrum of color of extraordinary breadth, meaning this range and chromatic purity that a display is capable of playing. The red, green and blue LEDs used in Led display walls emit a range of wavelengths much narrower than a source of white light and broad spectrum, such as a lamp. This circumstance allows the reproduction of a more deeply saturated colors and extends the range of reproducible colors.
Another strong point of the walls of Led display is the long life of the pixels themselves. The life of a source of light of a display is frequently defined as the number of elapsed hours to reach half the original brightness. Measured that way, the Led - no matter if they are used only as a source of light or directly as pixels on a Led display wall - usually last more than lamps.
All the displays consume energy and require cooling, but not all display technologies behave in that regard in the same way. On the walls of Led display, energy consumption is much more efficient than in most other technologies. That improving energy efficiency can be up to 400% or more, depending on the comparative systems.
Which translates in less heat and less perceptible noise device cooling required to dissipate the heat. Indeed, the temperature which operate some mosaics Led obviates the use of fans, always, that Yes, that the space between them is adequate and they have appropriate HVAC.
An important image in any display parameter is the size and the distance between pixels. How minors are these, closer to the image observer may be positioned before you begin to distinguish individual pixels.
A low indicator also suggests the possibility of concentrating a set number of pixels in a small area or, on the contrary, placing many more pixels in a given space. However, not all applications should be reduced between pixels away.
In the case of large displays, a distance between pixels too small can finish taking a pixel count much higher which requires a particular application. Luckily, Led tiles are available in a wide range of distances of pixel, ranging from 20 mm to just one. The distance reduced pixel is used mainly in interior spaces.
Very important is also the FILLFACTOR of the individual pixels, i.e., the relationship between the area of the generator element of light within a pixel (in this case the own Led) and the total area of the pixel. The higher the fill factor, more homogeneous will be the image and more the observer may be approaching the display unless the pixels become visible.
Another feature of this types of walls is that divisions in the images are imperceptible. A Led display wall mosaics are designed so that even if they touch, the distance between pixels does not increase to the next mosaic tile. In addition, the type of environment in which tend to place the Led of a typical mosaic makes it difficult to perceive the point from a distance of normal observation.
There are a variety of mosaics Led display on the market, which are mainly divided into indoor and outdoor models. The distance between pixels that we just show is more a point of differentiation. What all of these products have in common is their strong modularity. The small form factor characteristic mosaics Led facilitates the creation with size, appearance or configuration you want.
Led tiles tend to be also very thin, often less than 10 cm thick, which facilitates installation in the curve. Depending on the radius of curvature and mosaic model, they can adapt both concave and convex curves. The usual small size of the Led tiles offers great flexibility in considering the dimensions or shape.
One of the most important factors when purchasing a wall of Led display is the distance between pixels. The optimal distance between pixels depends on the number of pixels you want for the final image, as distance to which we hope the observer is situated.
By way of example, Figure 1 illustrates display wall sizes needed to achieve an image Full HD (1920 x 1080) with a whole range of distance in pixels. To achieve an image UHD (3840 x 2160), that sometimes we call 4 K, we can simply duplicate each linear dimension in the diagram. Of course, other aspect ratios and resolutions of final image are also possible.
There is no clear and precise rules regarding the optimum viewing distances for each distance between pixels. However, in table 1, we list some recommendations. The best distance of pixel for a given application will be that in which the vision of pixels is not annoying at a normal viewing distance, but allows the display dimension a significant portion of the field of view of the observer for the maximum impact to the proposed resolution.
Compared to other images display technologies, Led display walls have a number of advantages in terms of brightness, colour range, life, energy and form factor. In addition, they possess a unique ability to suit wide range of applications with different size, shape and distance viewing and environment requirements.
It is possible that the Led display wall between imaging technologies is a newcomer, but he managed as differentiated from all others. Their future can not be brighter.
Director of Christie for Spain and Portugal
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• Section: Control, Digital signage, Display, signs distribution, Projection, grandstands