Analysis of the principle of full-color LED advertising screen luminescence

The full-color LED advertising screen produces images and videos of different colors by emitting different colors of light. Its core component is the LED lamp bead. The full-color LED advertising screen is composed of several small particles. The overall brightness of a full-color LED advertising screen. Full-color LED advertising screens are divided into two types: outdoor and indoor. The brightness of outdoor full-color LED advertising screens must be greater than the light outside the human eye to see clearly. Indoor full-color LED advertising screens do not have such high brightness requirements. Color consistency is fine. There are two ways to increase the brightness of LED lamp beads. One is to increase the luminous amount of the chip itself; the other is to effectively use the light generated by the chip to increase the amount of light irradiated in the expected direction.

The former is to try to improve the luminous efficiency of the active layer of the chip, and to improve the shape of the chip to increase the efficiency of external light extraction, or to enlarge the chip and use high-density current to increase the amount of luminescence; the latter is to use light wave control technology, that is, to use packaging resin to form a special The optical structure allows the light generated by the chip to shine in the expected direction. If the full-color LED advertising screen finds that the brightness cannot reach the expected value after use, you can also try to increase the brightness with the following methods. 1. Change the current flowing through the LED. Generally, the LED tube allows a continuous working current of about 20 mA. Except for the saturation phenomenon of the red LED, the brightness of other LEDs is basically proportional to the current flowing.

2. The serial transmission content of the scanning board is not the switching signal of each LED but an 8-bit binary brightness value. Each LED has its own PWM to control when it is lit. In this way, in a cycle of repeated lighting, each pixel only needs 4 pulses at 16 gray levels, and only 8 pulses at 256 gray levels, which greatly reduces the serial transmission frequency.

With this method of decentralized control of LED gray scale, 256-level gray scale control can be easily realized. 3. Utilize the visual inertia of the human eye and use the pulse width modulation method to achieve grayscale control, that is, to periodically change the light pulse width (that is, the duty cycle), as long as the cycle of repeated lighting is short enough (that is, the refresh rate is high enough) ), the human eye does not feel that the luminous pixels are shaking. Since pulse width modulation is more suitable for digital control, today when microcomputers are commonly used to provide full-color LED advertising screen content, almost all LED control systems are usually composed of three parts: the main control box, the scanning board and the display and control device.

The main control box obtains the brightness data of each color of a screen pixel from the display card of the computer, and then redistributes it to several scanning boards. Each scanning board is responsible for controlling several rows (columns) on the full-color LED advertising screen, and each row The display and control signals of the LEDs on the (column) are transmitted in series. At present, there are two ways to serially transmit display control signals: one is to centrally control the gray level of each pixel on the scanning board, and the scanning board decomposes the brightness value of each row of pixels from the control box (that is, pulse width modulation). Then, the turn-on signal of each row of LEDs is transmitted to the corresponding LED in a row-by-row series in the form of pulses (1 when it is lit, 0 when it is not lit) to control whether it is lit. This method uses fewer devices, but the amount of data transmitted in series is larger, because in a cycle of repeated lighting, each pixel needs 16 pulses at 16 gray levels, and 256 gray levels. 256 pulses, due to the limitation of the working frequency of the device, generally can only make the outdoor LED advertising screen achieve 16 gray levels.

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