The Composition Of Large LED Advertising Screens

In the full-color large LED advertising screens currently on the market, each pixel unit is composed of red, green, and blue LEDs, and various colors can be generated by controlling the monochromatic gray level of the three LEDs in the pixel. The arrangement of the three LEDs in the pixel is earlier a zigzag arrangement of one red, one green, and one blue, similar to the arrangement of color TV phosphors, as shown in Figure 2.6.

Later, taking into account the luminous efficiency of the large LED advertising screen pixels, a four-light combination of two red, one green, and one blue appeared, as shown in Figure 2.7.

Full-color large LED advertising screens system, as the best large LED advertising screens system, is mainly composed of five parts: signal source, data transmission system, LED control system, LED drive system, and screen body, as shown in Figure 2.8. The signal source is from a wide range of sources, in addition to the general computer text, images, and video, but also cameras and video recorders and other filmed content. The control system is used to convert the signal obtained from the data transmission system into a control signal that can be received by the large LED advertising screens. And the drive large LED advertising screens system plays a key role in the final display, due to the large display area and the principle of cascade display, the large LED advertising screens drive system receives the signal from the control system, in addition to transmitting the data at this level to each display unit at this level, but also to transmit the signal that does not belong to this level to the next cascade of drive units.

Working Principle Of Large LED Advertising Screens

Data show that when the large LED advertising screens light source suddenly disappears, the human eye's brightness sensation does not disappear immediately, but gradually decreases according to the exponential law, which is called the visual inertia of the human eye. Therefore, when a large LED advertising screens light source is frequently connected and disconnected, the human eye can feel the brightness change when the rate of disconnection is slow, i.e., the frequency is low; and when the frequency of disconnection increases to a certain level, the human eye will not be able to feel the large LED advertising screens brightness change and will think that the scene is seen continuously. Usually will not cause a flickering feeling of the lowest repeated pass frequency is defined as the critical flicker frequency. The critical flicker frequency of the human eye is about 24Hz, so when the large LED advertising screens frame rate is 24 frames per second, the human eye sees a continuous image. Similarly, in daily life, people usually think that a fluorescent lamp is always on when it is actually turning on and off at a frequency of 50 times per second.

Visual inertia is the physiological basis for the widespread use of large LED advertising screens. Taking advantage of the visual inertia of the human eye, the design of LED drive circuits has been improved, resulting in the scanning drive method that is now widely used in large LED advertising screens. Instead of creating a separate driver for each LED, the scanning drive method combines several LEDs into a group and uses a common driver circuit. Through the dynamic scanning method, each group of LEDs is controlled to light up and down in turn. When the scanning frequency is greater than the critical flicker frequency, all LEDs are lit to the human eye. Since large LED advertising screens usually consist of thousands of LEDs, the scanning driving method is very important in terms of energy saving.

It is the combination of different light intensities of red, green, and blue LEDs that finally realized the display of color images, but the ratio of the three primary colors is not a simple superposition but needs to pay attention to the following issues.

(1) the ratio of red, green, and blue light intensity shall be close to 3:6:1.

(2) because the human eye vision is more sensitive to red, the distribution of red light sources in space should be more dispersed.

(3) taking into account the human eye's vision of red, green, and blue three different non-linear responses, in the terminal display; should be corrected for three primary color signals.