LED display common vocabulary understanding

LED screens are divided into graphic screens and video screens, both of which are composed of LED matrix blocks. Graphic screens can display Chinese characters, English text and graphics synchronously with computers; video screens are controlled by microcomputer ICs, with graphics, text and videos, and play various information in an instant, synchronous and clear information dissemination method. They can also display 2D, 3D animations, videos, TV, DVD/VCD programs and live events. Its advantages: high brightness, low operating voltage, low power consumption, miniaturization, easy matching with integrated circuits, simple driving, long life, impact resistance, and stable performance. It is widely used in stations, docks, airports, shopping malls, hospitals, hotels, banks, securities markets, construction markets, industrial enterprise management and other public places. Some other display technologies, such as LCD, electromechanical structure screens and light bulb displays, still have certain uses in certain specific occasions, but LED screens have been proven to be the most reliable, efficient, energy-saving, bright, and technically the most convenient to implement.

LED is the abbreviation of light emitting diode, or LED for short. The principle of LED luminescence technology is that certain semiconductor materials will emit light of a specific wavelength when current is passed through them. The conversion efficiency of electricity to light is very high. By performing different chemical treatments on the materials used, LEDs of various brightness and viewing angles can be obtained. It is a screen that displays various information such as text, graphics, images, animations, market conditions, videos, and video signals by controlling the display mode of semiconductor light emitting diodes.

The following are explanations of the standard terms and concepts commonly used in LED screens. I hope it will be helpful to everyone:

PIXEL

It is the smallest unit on the screen that can be controlled independently. PIXEL is the abbreviation of picture element. On the three-primary color screen, a pixel is composed of three parts: red, green, and blue. Each part is composed of one or several LEDs. In theory, by adjusting the brightness of red, green, and blue respectively, any color can be displayed.

PITCH

The center distance between adjacent pixels. The smaller the spacing, the shorter the visible distance.

Resolution

Commonly used in digital display devices to indicate the total number of pixels, usually written in the form of width x height, such as 800X600.

Viewing Angle

When an observer faces an LED, he or she can see the maximum brightness of the LED. When the observer moves to the left or right, the brightness seen will decrease. When the brightness is reduced to half of the maximum brightness, the angle at this time plus the angle obtained by moving in the opposite direction is called the horizontal viewing angle. The vertical viewing angle is measured in the same way. The viewing angle of the LED will be given by the manufacturer.

Brightness

Brightness is the most important parameter in any display device. The main unit of brightness is called candela, expressed in CD. The brightness of a single LED is usually expressed in millicandelas, MCD, which is one thousandth of a CD. Adding the brightness of a square meter of LEDs together, we get the brightness per unit area, expressed in nits (NITS). 1 NITS = 1 CD/m2

Viewing Distance

For various display devices, the optimal viewing distance should be the minimum distance at which the human eye cannot distinguish pixels, which is about 3400 times the dot pitch. The viewing distance of TVs and computers is usually less than this requirement, but the acceptable distance cannot be less than 1700 times the dot pitch.

Refresh Rate

The rate at which the screen image is updated, usually expressed in Hertz (Hz), is different from the frame rate.

Frame Rate

The number of image frames displayed on the screen per second, usually depends on the input signal (25 fps for PAL, 30 fps for NTSC)

Field

Half frame of PAL and NTSC, because PAL and NTSC are interlaced scanning, only half of the frame image is displayed each time it is refreshed.

Pure green and true green

In the past 30 years, various color LEDs have been developed one after another. First, red, yellow, yellow-green, blue LEDs and pure green LEDs were invented by Nichia engineers in the 1990s. Since then, it has become possible to manufacture full-color LED screens. LED screens that play videos must use pure green. If they are made of yellow-green, the color will definitely not be real. If there are many green tubes in a pixel, more than the number of red and blue tubes, then it must be a yellow-green tube, because the brightness of yellow-green is not enough, so multiple must be used, but yellow-green LEDs are cheap. This kind of screen is commonly known as a pseudo-color screen.

Color Temperature

The brightness of the three colors of red, green and blue must be balanced to accurately restore the true color. In other words, the white of the LED must be white, not pink. If red, green and blue are all at the highest brightness, the mixed color is usually not white. In order to obtain white (usually called 6500K color temperature), the brightness of one or two of red, green and blue must be lowered. In order to obtain the correct white, the brightness must be repeatedly measured and adjusted. This process is called white balance.

Grey Levels

The number of colors that an LED screen can display depends on the grayscale of the three colors RGB. In a standard full-color screen, there are 256 grayscales. For the full-color LED system of a stadium, 256 grayscales are not enough and cannot accurately restore the colors. Also known as color depth, it refers to the number of different brightnesses. Red, green, and blue have their own grayscales. In a full-color system, there are generally 256 grayscales, which can produce 256X256X256=16,777,216 colors. It is called 24-bit color in a PC and 8-bit system in an LED display system.

Gamma correction

This is a method of reducing the number of grayscales through a transformation function, thereby producing a color and contrast that is closer to the real environment. The colors actually displayed by the full-color screen are subject to many restrictions. At night, the screen brightness must be reduced, and the colors that can be displayed will be reduced. Therefore, the colors displayed by digital RGB must be less than 16M colors. In order to solve this problem, a higher level of grayscale is required. The 1Bill color system (1024 levels of red, green and blue each) can display more realistic colors, because the grayscale is expanded from 256 levels to 1024 levels, which greatly enriches the number of colors that can be displayed.

Virtual Resolution

Also known as shared pixels or dynamic pixels, pixels that are four times the number of physical pixels are quickly sent to the physical pixels four times according to odd-even columns and odd-even rows for display. The effect is equivalent to reducing the spacing by half. The cost is basically the same as that of traditional methods, but the resolution can be four times the original.

Uniformity

The quality of the entire picture depends largely on the consistency of LEDs. The problem of consistency is an inherent problem of LEDs when they are produced. Their brightness, viewing angle, and other characteristics are actually not uniform. These parameters are distributed in a certain range. The better the manufacturer's process control, the smaller this range. Selecting LEDs provided by high-quality manufacturers can reduce the workload of debugging. The human eye is very sensitive to color and brightness, and it is easy to detect the difference between LEDs. Especially in high-brightness display systems, this difference is even greater. Designers must use various technologies to eliminate this difference and increase consistency.

Colour Shift

LED screens use a combination of red, green and blue to produce various colors, but these three colors are made of different materials, and the viewing angles are different. The spectrum distribution of different LEDs is also different. These observable differences are called color differences. When the LED is observed at a certain angle, its color changes. The human eye is better at judging the color of real images (such as movie images) than observing images generated by computers.