Advantages of LED screens
The main advantage of LED screens, ensuring their ever wider distribution is a long service life (up to 100 thousand hours, or more than 10 years of continuous operation), high reliability, if necessary - extremely high brightness and all-weather conditions, which allows them to be used in street conditions when sunlight.
LED (Led) screen belongs to the class of active screens, i.e. The surface of the screen is both a modulator and a light source, unlike projectors, video cubes and other devices in which the light source is separated from the screen. With direct sunlight, the image of the LED screen does not lose contrast, especially when using gray filters that weaken the external light.
The LED screen installed indoors does not require internal cooling (fans), therefore such screens can be used in rooms with polluted air, in rooms where high demands are placed on low noise.
Light-emitting diodes. Pixel. Pitch pitch
Each LED (Fig. 1) emits a monochrome color of a certain wavelength - red, blue, green. To obtain a full-color screen, LEDs of all the specified colors are used.
Pixel. The smallest element of the image in the LED screen is the pixel. Each pixel consists of one or more LEDs (see Figure 2).
Pixel. The smallest element of the image in the LED screen is the pixel. Each pixel consists of one or more LEDs (see Figure 2).
Fig. 2. Pixel
In full-color screens, each pixel consists of red, green and blue LEDs, the total amount is usually up to 8 (but there are more). The built-in processor provides all basic colors and white with shades.
Pitch pitch. The physical distance between the centers of two adjacent pixels. The smaller the step, the higher the resolution, the higher the image quality, respectively.
Technology of manufacturing LED screens
При изготовлении светодиодных экранов используются разные методы компоновки светодиодов.
1. DIP Pixels. DIP - Eng. dualin-line package, also DIL - the name of the type of enclosure used for microchips, microassemblies and some other electronic components, including LEDs. Enclosures of this type are distinguished by their rectangular shape and the presence of two rows of pins on long sides.
In this variant, the pixels are separate groups of LEDs (most often these are three LEDs: R + G + B (red + green + blue), and you can also see other variations with 4 or more LEDs: 2R + 2G + B, 2R + 2G + 2B, etc., combined in one package.The drawbacks of this technology include insufficient color mixing and a large pixel pitch, the advantages are the possibility of using large diodes with great brightness and the use of more protected masks, so this technology is widely used in outdoor screens in increments of pixels from 10 to 50 m m.
Fig. 3. LED-screen. DIP pixels
2. Pixels of SMD. Somewhat later, than the DIP pixels, SMD technology (SMD, from the English surface mounted device) was used in LED screens. In this case, the microscope sized LEDs are placed in a single body (pixel), which is soldered directly to the printed conductors (Fig. 4).
Fig. 4. LED-screen. SMD Technology
The applied sizes of SMD pixels are currently 0.9 to 10 mm. The small size of the pixels makes it possible to achieve a very high resolution. Such screens were first used only in premises, since the LEDs were moisture-permeable and had a relatively small brightness. However, recently, due to bright LEDs and a special waterproof cloth, screens of this type have been successfully installed on the street.
3. LED clusters are radiating devices with a number of LEDs placed in a common waterproof and light-insulated housing. One cluster corresponds to one pixel of the image. The technology is used to produce large outdoor screens (Figure 5).
Fig. 5. LED-screen. LED cluster
4. LED matrix - a set of diodes on the surface of the screen. Here the pixel is not structurally formed, but each LED belongs to a strictly defined pixel, and the control is performed by the pixel as a single unit. This technology is used in the manufacture of screens for work both outdoors and indoors (Figure 6). At the moment, the technology is obsolete and is not used.
Figure 6. LED screen. LED Matrix
5. Virtual pixels. Here, the LEDs are not fixed to specific pixels, programmatically, the pixels from several neighboring LEDs are created in a timely fashion. This allows an artificial way to significantly increase the screen resolution. When you combine pixels both vertically and horizontally, the number of visible pixels doubles. It turns out a very high-quality image, as if on the screen four times more pixels (Figure 7). At the moment the technology is outdated and not used.
Figure 7. LED screen. Virtual pixels
Module. Pixels (as well as clusters) are combined into standard structural elements - modules having different sizes for different manufacturers, for example: 130x65 mm, 160x160 mm, 256x255 mm, etc. The module is a special board, which is built-in from the front side light-emitting diodes (this operation is carried out in factories by special automatic machines), and electronic components are placed on the back side (Fig. 8).
Fig. 8. Module of the LED screen
The module of the LED screen includes a certain number of pixels depending on their diameter. Modules are the basic elements which are subject to changeover in case of failure of LEDs, a certain number of modules always include in ZIP composition.
Office (panel). In most cases modules integrate in large structural elements – the offices (or panels) containing a certain number of modules (fig. 9). The size of an office is multiple to the sizes of modules. So, the office can have the size of 960х960 mm and include everyone in the composition of 36 (6х6) modules of 160х160 mm in size. Other example: the office of 1024х768 mm in size containing 12 (4х3) modules of 256х256 mm in size. The linear sizes of offices from 0,5 to 2 m, thickness are about 175 mm (sometimes less). The appearance of an office (in front and behind) is illustrated by the photo (fig. 9). As a part of offices surely there are power supplies. Offices fasten to each other without gaps that allows to create a uniform screen cloth. Room creation allows to create screens of any sizes, saving at the same time their mobility and maintainability.
Fig. 9. LED office – the screen
The casing of an office is usually executed from steel, at the same time the weight of 1 sq.m of a screen surface is 65-70 kg for Outdoor screens and about 35 kg for Indoor screens. However also aluminum casing (27 kg on 1 sq.m) and the carbonic casing is issued (20 kg on 1 sq.m). Such facilitated offices, as a rule, apply to the screens intended for rent use where it is important to reduce weight of the moved and mounted equipment.
LED offices – screens happen two types - to back fixing and to front fixing.
Back fixing requires use of the special construction providing easy access to back parts of offices during the mounting and service. Offices with front fixing use when approach to offices is behind difficult. Some companies release the universal offices suitable both for back, and for front fixing.
The LED screen - a grid. There are also easy screens grids, or the flexible translucent screens having a big stride and used for street illuminations as backs of theatrical scenes, etc. where high resolution is not required (see fig. 10).
Figure 10. LED screen - grid
Main technical characteristics of the LED screen
- Graphic definition: the number of pixels available on the screen. It is indicated as follows: horizontal resolution x vertical resolution. For example: 400x300.
- Brightness (Standard brightness): brightness of the light emitted by the module, measured in candelas per square meter (NIT). For outdoor screens, the brightness is between 6000 and 12000 cd / m2. For screens used indoors (Indoor), enough brightness within 1000-3000 cd / m2.
- Viewing angle: shows the actual viewing angle at which the brightness of the image falls two times relative to the brightness at a perpendicular view. The viewing angle can be in the range from 100 to 160 degrees.
- Power Consumption: the average is usually in the range 250-300 W / m2, the maximum (peak) 750-900 W / m2.
Indoor screens are designed for normal room temperature and humidity. If the screen is designed to work in conditions of high humidity (for example, in a pool, on a rink, etc.), a special protective film is used.
Outdoor screens have a degree of protection IP65 / IP46 (front / rear) and can operate at temperatures from +30 to -30ºC. When operating outdoor screens in Russia, in some cases, it is necessary to provide a ventilation or air conditioning system so that the screens can work both at high and low ambient temperatures.
Selecting the screen format
It is always preferable that the LED screen has a format corresponding to the standard format of computer and video materials, i.e. 4: 3 or 16: 9. Otherwise, the preparation of content will be very difficult. Thus, with a 4: 3 format, the recommended screen sizes will be, for example, 2x1.5 m 3x2.25 m, 4x3 m, 6x4 m, 8x6 m, etc. With a 16: 9 format, 2x1,125 m, 3x1, 68 m, 4х2,25 m, 6х3,375 m, 8х4,5 m, etc. However, in some cases screens with non-standard format are used.
Select pixel pitch
a) It is generally accepted that the LED screen providing acceptable image quality must have a graphic resolution of at least 256х192 pixels (with a 4: 3 screen format). For example, for a screen with dimensions of 6x4 m, the pixel pitch should be no more than 23.5 mm, for a screen with a size of 3x2.25 - no more than 11.75 mm. Naturally, the smaller the step, the better the image quality.
b) The second limiting parameter is the viewing distance.
The minimum viewing distance, expressed in meters, at which the image looks satisfactory, in the first approximation is equal to the pixel pitch, expressed in mm. At a shorter distance, the pixel structure of the image will be noticeable, which irritates viewers. For example, with a pixel pitch of 16 mm, the minimum distance is 16 m, with a pixel pitch of 4 mm, the minimum distance is 4 m.
The maximum distance for comfortable viewing can be estimated approximately by the formula: maximum distance (m) = 6 B, where B is the screen width in meters.
Outdoor screens usually use pixels in increments ranging from 6 to 40 mm.
Currently, the most common step for large street screens is 16 mm.
Indoor LED screen can have a step from 1.2 to 10 mm, and in the near future the step will become even smaller. The smaller the step, the more expensive the screen.
Flexible LED screen-grid can have a step of pixels from 10 mm to any value specified by the Customer.
Selecting the type of LEDs
The cost (and quality) of the LED screen depends not only on the pixel pitch, but also on the type of LEDs used. The most high-quality and, correspondingly, the most expensive LEDs are the Japanese Nichia, followed by the American Cree, then the whole group: Taiwanese Epistar, Korean Samsung, Chinese advanced (LEDs made in China, based on Taiwanese Epistar chips), and finally - the most common Chinese Silan. The difference in cost can go up to two or three times with similar technical characteristics. Quality is expressed in reliability and service life of LEDs, as well as in the identity of LEDs in terms of brightness and color gamut.
Светодиодные экраны способны воспроизводить видеоизображение с различных источников:
- Computer networks (including the Internet and Intranet)
- Videoconferencing systems
- DVD players
- Satellite and cable television receivers
- Industrial video surveillance systems
LED Display Control
The LED screen in its composition necessarily has in the necessary amount of transmitting and receiving cards (Sending Cards, Receiving Cards), providing the transmission of control signals from the computer. Between the screen and the controller (Sending Cards) it is necessary to lay a signal cable of the "twisted pair" type, at a high resolution of the LED screen it is necessary to throw several cables. This cable path between the controller and Receiving Cards in the cabinets is possible at a distance of up to 100 m, otherwise you should switch to optical communication with the help of additional equipment. The control scheme of the screen is illustrated in Fig. eleven.
Fig. 11. LED screen. Connection and management
Installation of LED screens
Street screens can be installed on the roof of buildings, fixed on the walls of buildings, installed on special structures such as "legs". Inside the rooms, screens are attached to walls, installed on special racks, suspended on cables. In all cases, a project is being developed for the installation of a screen and the manufacture, if necessary, of special metal structures. When the screen is mounted on the roof or wall of the building, the building is inspected and calculations are performed to confirm the possibility of such installation. Receiving permission to install the screen and power supply is a function of the Customer.
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