Two control the brightness of LED

One is to change the current flowing through the led, the general LED tube to allow continuous current 20 mA or so, there is saturation in addition to the red LED, the other LED brightness is essentially proportional to the current flow.
Another method is to use the human visual inertia with a pulse width modulation method to achieve gray scale control, that is, periodic changes in pulse width (ie duty cycle), as long as the repeated cycle of light short enough (ie, refresh frequency is high enough), the human eye can not feel light-emitting pixels in the jitter. As the pulse width modulation is more suitable for digital control, so widely used computer to provide the RGB LED light today, almost all of the LED.
LED control system usually consists of the main control box, scan control board and display device has three major components. Main control box from the computer's graphics card to get a colored screen pixel luminance data, then re-assigned to the scan plate number blocks, each scan LED screen on the control board is responsible for a number of rows (columns), and each row (column) on the LED display control signal is transmitted with a serial manner. There are two serial transmission of display control signals: one is the centralized control panel scan grayscale pixels, scanning from the control panel box of the line pixel brightness value decomposition (ie, pulse width modulation), Then the opening of the line LED signals in pulses (light 1, off 0) by using serial transmission line to the corresponding LED on the control whether light. Devices used in this way less, but the serial transmission of data volume, because in a repeat cycle of light, each pixel in the 16 gray scale requires 16 pulses, required under the 256-level grayscale 256 pulses, the device operating frequency restrictions, can only do 16-level grayscale LED screen.
Another method is to scan the contents of the board is not a serial transmission switching signal for each LED but the brightness of an 8-bit binary value. Each LED has its own pulse width modulator to control the on time. Thus, in a repeating cycle of light, each pixel in the 16 gray scale only four pulses, 256 gray scale only 8 pulses, greatly reducing the frequency of serial transmission. In this method of decentralized control LED gray can be easily controlled with 256 levels of gray.