FAQ For LED display

 FAQ For LED display
LED screen, LED signs, LED billboard, LED floor

•  Q: What is the Maximum. Inter space (gap) between cabinets?
• A:  Inter space (gap) between cabinets within 1.5 mm for outdoor and 0.5mm for indoor.
• 2 Q: How to make the installation structure ?
• A: We offer the installation structure design drawings for customers, and the design can well fit your installation conditions.
• 3 Q: Do we need to follow some sequence in installation and keep every cabinet in its right position?
• A: All the cabinets are modular and every cabinet can be in any position, so there is no need to follow any sequence in installation since the sequence can be setup by software after installation.
• 4 Q: What is the cooling system of the display? Does the display need air conditioner?
• A: Every cabinet has fans for ventilation. We suggest customer to equip several industrial fans inside installation structure for ventilation instead of air conditioner.
• 5 Q: How to wire the cords and cables?
• A: Every cabinet one pair of power cords (output/input), and one pair of data cable (output/input), we make wiring instruction drawing for every order, customers only need to follow the instruction drawing.
• 6 Q: Which wiring is better, concealed wiring or exposed wiring?
• A: Concealed wiring is more stable since less connectors in wiring. Exposed wiring is more convenient for operation, and easier and faster for replace any cords or cables. For permanent installation, we recommend concealed wiring, for rental displays, we recommend exposed wiring.
• 7 Q: Can we do maintenance from front if the rear space of installation is very limited?
• A: Yes, some of our displays support front access, you can take out modules and other accessories from front side. The displays support front access are: outdoor P25, P20, P16, indoor P12, P10, P8 etc.
• 8 Q: What is the minimum resolution to play a video?
• A: W 256 x H 192 pixels = 49152 pixels
• 9 Q: What is pixel by pixel correction technology?
• A:
  Luminance and color uniformity are most important characters for led display. The root cause of luminance and color uniformity problems in LED screens is the LEDs themselves. First, the brightness of each LED varies widely even though they are driven by the same voltage and current. Second, the colors of the LEDs are also quite variable. Third, the LEDs get slightly dimmer as they are used. The blue LEDs dim the most and the red LEDs dim the least, but the biggest problem is that individual LEDs dim differently over time. So, even if an LED screen were perfectly uniform when it left the factory, it would loses its uniformity as the LEDs dim, and after about 2 years of usage it would begin to look quite non-uniform. When you add these three problems together you can see why achieving uniformity in a LED screen is so difficult.
  What’s an LED display Manufacturer to do to keep the uniformity? There are several methods can use to handle non-uniformity issues. The first method is to buy the LEDs from manufacturers in highly binned lots. Secondly, they can adjust the current to try to achieve luminance uniformity and thirdly, they can use PWM (Pulse Width Modulation) correction coefficients to achieve a high degree of both luminance and color uniformity. The second and third methods are what we called PIXEL BY PIXEL CORRECTION technology.
  The brightness of LEDs is determined by the amount of DC current that flows through the P/N junction. More current produces a brighter LED. Unfortunately, however, adjusting the current will also change the color of the LEDs. LED manufacturers can adjust the current applied to each pixel by adjusting a variable resistor for each leds on the module. This method can be used to make sure that the modules all have the same brightness, but it cannot be used to adjust the color differences. What’s more, if two modules were the same color before adjusting the current, they would not be the same color after the adjustment. This method is taking too much time by taking record to the brightness of each leds and adjusting the current individually.
  Pulse Width Modulation (PWM) is a widely used technique to control the brightness of LEDs. It can be used to process the video signal and also to perform uniformity correction. PWM is used instead of varying the current because changing the current of the LEDs would also change the colors as explained above. PWM works by flashing the LEDs either full on or full off at a very high rate. The flashes are so fast that the human eye cannot notice them and the duration of the individual flashes (pulse width) determines the perceived brightness. PWM uniformity correction works by modifying the pulse widths to compensate for LEDs that are naturally brighter or dimmer or display a different color. In a non-corrected system, the video signal is turned into pulse widths by the video controller and then sent to the LED drivers to flash the LEDs. In a corrected system, the pulse widths are multiplied by correction coefficients before being sent to the LED drivers. The actual process is a bit more complicated. Each pixel not only needs green correction, but red and blue correction as well. This means that a little bit of green and blue need to be added to red and a little bit of red and green need to be added to blue.
  However, pixel by pixel correction has high requirement on the accuracy of the equipment. Too much tolerance will also lead to the non-uniformity of led display.
• 10 Q: How to improve the brightness of LED display?
• A:
  LED brightness can be improved through the following two methods:
  1. To increase the light output of the chip itself: light output can be increased through improving the luminescence efficiency of the chip’s active layer or improving the external light extraction efficiency by optimizing chips’ shape or making larger scale chips that run high density current.
  2. To use the light effectively. In other words, to increase the amount of light that irradiate towards the needed direction. In this method, light wave control SHENZHEN LAMP TECHNOLOGY CO.,LTD FAQ-1.0V(2009) technology is used. Through a better design of the optical structure shaped by the packaged epoxy resin, the light can be controlled to shine towards expected direction, thereby improving the brightness of LED.
  The above are the methods to improve LED brightness, if the brightness of LED display runs under expectation, methods listed below can be adopted:
  1. To alter the current magnitude that runs through the LED. Generally, LEDs allow a 20mAmp operating current continuously. Only red LED has saturation phenomenon, other LEDs’ brightness are in direct ratio with the current amount that runs through them.
  2．To realize grey scale control through adopting PWM (Pulse-Width Modulation) method. That is to change the width of the light pulse (duty cycle) periodically. If the time for the relighting cycle is short enough (in other words, the refresh rate is high enough), the dithering of the luminescence pixel can not be felt by eyes thanks to the visual persistence trait. As it is more adaptive to adopt digital control to realize PWM, meanwhile, as microcomputer is widely used to provide the content to display in LED screens, nearly all of the LED control systems are composed by main controller, scanning board and display control device. Main controller firstly captures data of all colors’ brightness in one particular screen image from the display adapter, then to distribute the data to the scanning boards. Each scanning board takes charge of certain rows of the LED display and the LED display control signal in each row can be transmitted in serial mode. Currently, there are two serial modes to transmit display control signal. One way is to make centralized control of each pixel’s grey scale in the scanning board. More detailed steps: the scanning board analyzes the data of each row of pixel received from the controller (PWM process), then the board will transmit the open signal of each row to corresponding LED light, controlling each LED to be lit on or to keep off state. The signal is transmitted in serial mode and in the form of pulse (the pulse signal will be 1 if it indicates LED to turn on, contrary, the signal will be 0). The device used in this method is less, but the data amount being  transmitted is comparatively larger. In every relighting cycle, the grey scale level is in direct ratio with its pulse amount for each pixel, that is to say, 16 grey scale levels need 16 pulses and 256 grey scale levels need 256 pulses. As in LED display, the working frequency for the devices is limited, only 16 grey scale levels is achieved generally.
  3. The serial transmitting content for the scanning board is not the on or off signals of each LED, but an eight-bit binary brightness value. If every LED has its distinct PWM to control its lighting time, a pixel under 16 grey scale levels need only 4 pulses and 256 grey scale levels need only 8 pulses in one relighting cycle, reducing serial transmission frequency greatly. Through this grey scale decentralized control method, 256 grey scale levels control can be achieved easily.
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