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LED display operations
Glossary
 
LED
Semiconductor – diode emitting light when electric current flows through it.
 
DIP
Dual In-line Package of LED, usually elliptical with two outputs. DIP LED contains a chip of one color (green, red or blue).
 
SMD 3in1 LED
Consists of three light-emitting chips - one per each color (red, green and blue). One SMD 3in1 LED makes one pixel of a screen. It is not possible to count virtual pixels for this equipment.
 
Pixel
Basic pixel consists of LEDs of basic colors - Red, Green, Blue. White color is made by composition of basic colors with the approximate ratio of R:3, G:6, B:1
 
Pixel pitch
Distance between geometric pixel centers, usually in mm. Pixel pitch is directly related to the minimum viewing distance. The smaller the pitch, the shorter the viewing distance at which we no longer see individual pixels.
 
Real pixel
Consists of a three or four LEDs of primary colors in the configuration 1R1G1B or 2R1G1B. Two red LEDs (R) have been previously used for two reasons. The first was performance of red LEDs, which was not sufficient for the required ratio of color components in white (R: 3, G: 6, B: 1), the second was voltage of the LED, which was roughly a half of the blue and green. A pair of red LEDs connected in series voltage reached a similar green and blue. This simplified the connection design. Today, the production of the red LEDs is facilitated by chips with different composition and so the voltage and brightness are suitable for use of a single LED.
 
All leading manufacturers of LED screens using high quality LEDs nowadays use pixel configuration 1R1G1B. SMD 3in1 also contain one chip of each color. Sometimes, especially for Chinese manufacturers or their distributors we find that the reason for using two red LEDs to prevent some kind of overloading and other nonsense. The reason is one and only one - the lowest price of the final product.
 
Virtual pixel
This technology is based on simple geometric principles supported by avanced technology. When LEDs are properly evenly spaced, it is possible to create another - virtual - pixel can be created between the two physical ones. With this technique the virtual resolution can be doubled.
 
 
What does a LED display consist of?
Cluster or LED module
Cluster or LED module  is basic building block of the LED module. It is a small waterproof module containing LEDs and control electronics made of durable plastic. The arrangement, where the control electronics is directly on a cluster is also called "intelligent cluster".
Module
Module or the often used term cabinet is the basic building block of an LED display. It is completely made ​​of aluminum. Basic resolution of  modules ranges from 64x64 to 192x192 pixels. Module dimensions are based on the pixel pitch. In addition to these basic sizes we are able to adjust their size in increments given by size of the cluster. Depending on the purpose of the LED screen, there are modules either for fixed installation, with wiring inside the module, or in the form for rent with external wiring and cage construction with quick-releases for fast assembly.
Supporting frame
Supporting frame is used for transferring static and dynamic powers to the place of installation. It could be a roof, facade, pillar etc.
Control PC and LEDbow software
Control PC with installed  control card is used to play streamed content, for previewing, and to send diagnostic data about the status of the LED display. The computer is connected with the screen in optical path, allowing connection even over long distances with great resistance against interference with radio communications. For shorter distance it is possible to use ordinary CAT 5 cable.  software allows for complete remote management of the control PC. You schedule an advertising campaign on your computer and you transfer and execute the campaign and the ad spots over the Internet. You can control multiple LED displays on your network at once.
 
 
What parameters of LEDs are important?
Is the brand of LED important?
Very much! Use of quality LEDs considerably affects lifetime and durability but also price of an LED display. Even though comparison of basic parameters of LEDs by various manufaturers might not necessarily yield substantial differences there are quite a few. The most important difference is speed of ageing of the LEDs ( Nejpodstatnějším rozdílem je rychlost stárnutí LED diod (loss of light intensity over time).
 
Often quoted 100 000 hours of lifespan of an LED display is really based on declared lifespan of the diodes. Usually it is claimed that with permanent current 20mA, 25°C temperature the brightness of an LED drops by 50%. It doesn't mean that after 100 000 hours the LED is dead. Nobody shows, though, what the drop in brightness is over time. Majority of customers assumes linear recession; however it is not true. Only manufacturers of hight quality LEDs (NICHIA, CREE) will reach more or less linear recession. Cheap chips and LEDs will have a high loss at the beginning, after couple of thousands of hours the brightness will dip even to 60%.
 
Another parameter is "reliability" of a chip. It mainly means the size of the chip, it's resistance against electrostatic penetration, the ability of the housing to dissipate heat, build of the housing, durability against UV, material used for the conductors (more expensive copper, cheaper steel) etc.
 
How can I determine manufacturer of LEDs on my display?
Type of used LEDs cannot be precisely verified. LEDs are not marked on the housing. The only reliable pointer is respectability of the manufacturer. The origin of LEDs can be proved only by purchase receipt but even then it is not certain that the LEDs on your screen are the ones from the receipt. In addition number of less trustworthy manufacturers claim the use of CREE LEDs but in reality these are LEDs manufactured by them only containing CREE chips.
 
 
 
What parameters of LED display should I been interested in
Minimal viewing distance
The shortest distance from which you can see an image continuously without distinct pixels. The smaller the pixel pitch, the shorter the minimum viewing distance. A simple guiding rule is that the physical pitch of pixels in millimeters corresponds to the minimum viewing distance in meters.
Maximum viewing distance
Has nothing to do with the pixel pitch. Only the physical size of LED display is crucial. In other words, LED display must be so large, that even the longest desired viewing distance will provide clearly visible display content..
Number of colors and color processing
Displayable colors are the key features of LED displays. The higher the number of colors you have, the more advanced technology must be used. This parameter is often intentionally falsified by less reputable manufacturers. Some manufacturers are deceiving you “just a little”, when their management system works in signal processing with 12 to 16 bits per color component (during gamma correction), but thanks to the LED display drivers can display only 8 or 10 bits. Less significant bits are just discarded and unused. Even then manufacturers say that the system has 16 bits per color component.
 
LED displays  not only process the full 16 bits color component, but also display. This requires a sophisticated and expensive technology, but the final image is incomparably better.
Refresh frequency
very important parameter of LED display is the number of frames displayed per second. Any value below 200Hz is basically useless. If the refresh rate is low, the image of the LED display flashes, can’t be photographed and when the camera is filming the screen, you can’t see same image on the record.
 
Many manufacturers change the refresh rate depending on the size of the LED display, so larger have a lower refresh rate. It has to do with constant speed of image data transport and that is dangerous practice. LED displays  have always fixed refresh rate 400Hz or 800Hz regardless of the size of the LED display.
 
We also use a number of mechanisms designed to improve the final image and increasing virtual refresh rate. LED displays  are perfectly readable by cameras and digital cameras with a very fast shutter.
Brightness
When using LED screens outdoors, the minimum brightness must be at least 5000cd/m2, indoors 1500cd/m2.
Viewing angles
They are the viewing angles from the perpendicular to surface of a LED screen at which decreases brightness LED screen to 50% against the value of brightness along the perpendicular (0° - directly to the screen). Angle value depends on the LEDs. Horizontal viewing angles using conventional LED diodes (DIP) are 120-140° and vertical viewing angles are 60-70°. The 3in1 SMD LED diodes have both viewing angles 120-160°.
 
 
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