How to improve the brightness of LED display
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 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 20 milliampere 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.
TAG:  LED Display