The brightness of an LED large screen is fixed and generally uncontrollable. However, theoretically, there are two control methods:
1. The receiver card serially transmits not the on/off signals for each LED, but an 8-bit binary brightness value. Each LED has its own pulse width modulator to control its illumination time.
Thus, within one repeated illumination cycle, each pixel requires only 4 pulses for 16 grayscale levels and only 8 pulses for 256 grayscale levels, significantly reducing the serial transmission frequency. This distributed control method of LED grayscale can easily achieve 256-level grayscale control.
One method involves changing the current flowing through the LED display screen. Generally, LED tubes can operate continuously at around 20 mA. Except for red-chip LEDs which exhibit saturation, the brightness of other LED tubes is basically proportional to the current flowing through them.
This method utilizes the visual inertia and poor visual impression of the human eye, using pulse width modulation (PWM) to achieve grayscale control. This involves periodically changing the width of the light pulse (i.e., the duty cycle). As long as this repetitive lighting cycle is short enough (i.e., the refresh rate is high enough), the human eye cannot perceive the flickering of the light-emitting pixels.
Because PWM is more suitable for digital control, almost all LED displays today use PWM to control grayscale levels, especially since microcomputers are commonly used to provide the content displayed on LED screens.
Extended Information: An LED control system typically consists of three main parts: the main control box, the scanning board, and the display control device. The main control box obtains the color brightness data of a screen's pixels from the computer's graphics card, and then redistributes it to several scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED screen, and the display control signals for each row (column) of LEDs are transmitted serially.
Currently, there are two methods for serially transmitting display control signals: one is that the scanning boards centrally control the grayscale of each pixel. The scanning boards decompose the brightness values of each row of pixels from the control box (i.e., pulse width modulation), and then transmit the LED on/off signals of each row of LEDs in pulse form (1 for lit, 0 for unlit) serially to the corresponding LEDs, controlling whether they are lit.
This method uses fewer components, but the amount of data transmitted serially is larger because, within a repetitive lighting cycle, each pixel requires 16 pulses for 16 grayscale levels and 256 pulses for 256 grayscale levels. Due to the limitations of the device's operating frequency, the LED screen can generally only achieve 16 grayscale levels.
This method uses fewer components, but transmits a large amount of data serially. This is because each pixel requires 16 pulses at 16 gray levels and 256 pulses at 256 gray levels within a single cycle of repeated illumination. Due to the limitations of the device's operating frequency, LED screens can generally only achieve 16 gray levels.
