LED display terminology

LED display terminology

Color matching, white balance

White is red, green and blue three colors according to the brightness ratio of mixing, when the brightness of green in the light is 60%, the brightness of red is 30%, the brightness of blue is 10%, the human eye feels pure white after color mixing, but the coordinates of LED red, green and blue can not achieve the effect of full chromatography due to the process and other reasons, and control the brightness of the primary color including the deviation of the primary color to obtain white light, called color matching, when the color matching for the full-color LED display, in order to achieve the best brightness and the lowest cost, The three primary colors should be selected as much as possible to form pixels of LED devices with a ratio of roughly 3:6:1, and the white balance requires that the three primary colors are still pure white under the same gray tone value.

Resolution

Resolution (Resolu port, station called interpretation): is the precision of the screen image, refers to the number of pixels that the display screen can display, because the dots, lines and surfaces on the screen are composed of pixels, the more pixels the display can display, the more fine the picture, the more information can be displayed in the same screen area, so the resolution is a very important performance indicator of pixels (Pixel): The minimum luminous pixel of the LED display is the same as that of ordinary computer monitors" Pixels have the same meaning.

Brightness

Brightness refers to the brightness of the picture, measured in candela per square meter (d/m2) or nit, simply put, the light intensity emitted by one square meter of display.

There are 4 commonly used physical quantities of light, which are:

1. Luminous intensity, is the luminous intensity of a light source in a given direction, the unit candela, della, referred to as kan, cd

2. Luminous flux, the amount of light emitted by the light source per unit time is called the luminous flux of the light source, unit lumens, 1m

3. Illuminance, 1m (lumens) of luminous flux evenly distributed on the surface of 1m2 produced illuminance, unit lux, 1x.

4, brightness, unit light source area in the normal direction, unit solid angle in the light flow, unit nits, n11 It should be noted that brighter products are not necessarily better products, the display screen is too bright often makes people feel uncomfortable, on the one hand, it is easy to cause visual fatigue, but also to reduce the contrast between pure black and pure white, affecting the performance of color levels and grayscales, so improve the brightness of the display screen at the same time, but also improve its contrast, otherwise the entire display screen will appear white. In addition, the uniformity of brightness is also very important for the uniform brightness of the picture, soft and sunny, and no obvious dark areas. Maximum display brightness: Under a certain ambient illumination, the brightness of the primary color of the LED display at the maximum brightness and maximum gray level.

Contrast

Contrast refers to the ratio between the brightest and darkest areas of the projected image, the larger the ratio, the more gradient from black to white, so that the richer the color performance, the impact of contrast on the visual effect is very critical, generally speaking, the greater the contrast, the clearer and more eye-catching the image, the more vivid and vivid the color: The contrast is small, it will make the whole picture gray, high contrast for the clarity, detail performance, grayscale performance of the image are of great help, the higher the contrast, the better the image effect, the color will be more saturated, Conversely, if the contrast is low, the picture will appear blurry and the colors will not be sharp.

Contrast refers to the measurement of different brightness levels between the brightest white and the darkest black in the light and dark areas of an image, the larger the difference range represents the larger the contrast, the smaller the difference range represents the smaller the contrast, a good contrast ratio of 120:1 can easily display vivid and rich colors, when the contrast ratio is as high as 300:1, it can support all levels of color but the contrast ratio suffers from the same dilemma as brightness, there is no effective and fair standard to measure the contrast ratio, so the best way to identify is to rely on the user's eyes.

Grayscale level

Grayscale is also the so-called color scale or grayscale, refers to the brightness of the degree of brightness, for digital display technology, grayscale is the determinant of the number of colors displayed, in general, the higher the grayscale, the richer the color displayed, the more delicate the picture, easier to express rich details. For example, a company's display screen adopts a 16-bit processing system, that is, 65536 levels of grayscale, and the three primary colors of RGB can constitute 655365536*65536 colors.

Refresh rate

The refresh rate of the display is the number of times the display screen is repeated by the display in hertz (Hz). The higher the refresh rate, the less flickering the image on the screen, the higher the stability, in other words, the better the protection of vision. Generally, people's eyes, not easy to detect the flickering sensation brought by the refresh rate above 75Hz, some companies can increase the display frequency up to 4800HZ, so that the background effect of TV recording completely gets rid of the troubles of water ripples, mosaics, etc., giving people a fresh and comfortable and transparent feeling, and can do live broadcast.

The number of colors displayed

Refers to the number of colors that the display screen can display, the more colors displayed, the more delicate and soft the image. If each of the three colors of red, green, and blue can display 65536 colors, then the three colors can display 65536*65536*65536 colors.

Temperature

Color temperature (colour temperature): indicates that the most common indicator of the spectral quality of the light source color temperature is defined by the absolute black body, the radiation of the light source in the visible area and the radiation of the absolute black body is exactly the same, at this time the temperature of the black body is called the color temperature of the light source Low color temperature light source is characterized by energy distribution, red radiation is relatively more, usually called "warm light"; After the color temperature increases, the proportion of blue radiation in the energy distribution increases, commonly known as "cold light" The color temperature of our display is adjustable at 35009000.

Uniform color

Color uniformity generally refers to the consistency of brightness and chromaticity of various parts of the display, and the quality of color uniformity has a lot to do with the display effect of the display.

The inconsistency of LED brightness and chromaticity affects the display effect of the electronic display, resulting in bad display effects such as flower screens, mosaics, etc., because the chroma of the LED will change more obviously with the change of current, PWM pulse width modulation is generally used to adjust the LED brightness. The chromaticity and brightness correction of the pixel is achieved by adjusting the red, green and blue components of the point separately, for each pixel that needs to be corrected, a 3*3 correction coefficient matrix is required to multiply it, and the LED is driven by the pulse width corresponding to the correction coefficient, so that the brightness and chromaticity of the entire display screen are highly consistent. The correction technology has developed from simple light intensity correction to light intensity + color coordinate correction The brightness and chromaticity difference between our display modules can be less than 5%.

Error detection

The error test is based on point-by-point detection on the basis of the system does not need to turn off the display screen and light each LED light when detecting, and the system can be controlled remotely, from the surface to the scene without going to the scene, the repair personnel do not need to go to the site to know the coordinate data of each dead point.

Point-by-point correction

The principle of point-by-point correction is to measure the brightness of each 1ED lamp under the same working conditions, and then calculate the correction coefficient of each lamp according to the set target value, and adjust the amplitude or duty cycle of the driving current with the coefficient, so that the brightness of each lamp reaches the set target value, and the brightness of the display screen decreases after correction, but the overall effect will be improved.

Color gamut diagram (CiE)

In order to be able to visually represent the concept of color gamut, the CIE International Illumination Association has developed a method for describing color gamut: CIE-xy chromaticity diagram.

The color gamut range that the display device can express is represented by the triangle area composed of RGB three-point lines, and the larger the area of the triangle, the larger the color gamut range of the display device.

power

The electrical power indicates the speed of the consumption of electrical energy, and the electrical power is represented by P, its unit is watts (Wat), and the abbreviated watt (Wa) symbol is W.

The maximum power of our display refers to the maximum input power required by the display when it is working, that is, the power required by the display when the white brightness value of the display is hit to the highest. Average power refers to the average power required by the display for a certain period of time during normal operation, which is related to the content played by the display. The average power is 30-60% of the maximum power.

Power meter

The power meter is an instrument used to measure the power of the display screen, which can quickly and intuitively display the voltage, current, power consumption and other values of the cabinet.

Drive mode

Constant current refers to the current value specified during the constant output design in the allowable working environment of the driver IC; Constant voltage refers to the voltage specified at the time of constant output design in the allowable operating environment of the driver IC.

1. There are two driving modes: constant current drive and constant voltage drive. Constant current drive is better and more expensive (more circuit boards and chips keep the current constant, increasing the service life and stability of the LED display).

2. The difference between dynamic control and static control: Dynamic control saves the cost of the driver chip, saves electricity (brightness and small power is also small), and in the case of the same specification of the same lamp chip, static scanning is brighter than dynamic scanning.

3. Commonly used scanning methods are as follows, /16 scan, 1/8 scan, 1/4 scan, static scanning, the first three are dynamic scanning, 16 lines of one scan, 8 lines of one sweep, 4 lines of one sweep.

4. The working principle of scanning is to use the visual retention characteristics of the human eye, in a short period of time to light up each row of the LED display separately, that is, the light on the screen is not fully bright, but we look all on, and animation, slow looks like a picture effect, fast as if moving, static screen is corresponding to the scanning screen, static screen refers to the LED display in the display of text, images, video, The light points on the LED display are lit up at the same time when displayed; Instead of using the visual persistence characteristics of the human eye like the scanning screen, in a short period of time the LED display of each row respectively lit, as we all know, LED display is the use of duty cycle to drive, so, the brightness of the display and the lighting time period has a lot to do, so, in the same case of the same luminous tube brightness, the static screen is higher than the brightness of the scanning screen, so the static screen is commonly used in the case of high brightness display outdoors, and the scanning screen is commonly used in the case of low requirements for brightness indoors, In order to save driving costs, but with the continuous maturity of LED material technology, the brightness of LED light-emitting tubes continues to increase. Now there is also a way to use scanning to make LED displays outdoors to save costs. Of course, the use of the scanning screen outdoors has very high requirements for the control and driver parts, and the performance requirements for the driver chip are also extraordinary.

Constant current drive of the LED

When LEDs are used as displays or other lighting fixtures or backlights, they need to be driven by constant current, mainly because:

1. Avoid driving current exceeding the maximum rating and affecting its reliability.

2. Obtain the expected brightness requirements and ensure the consistency of each LED brightness and color.

3. It can effectively avoid lightning strikes, power grid surges, overcurrent, overvoltage protection, so that the LED life is extended. There is a problem: to deal with the heat dissipation problem, the heat dissipation problem is not handled well and affects the LED life.

MTBF

MTBF, that is, mean time between failure, the full name of the English is "Mean Time Between Failure" is to measure the reliability index of a product (especially electrical products), the unit is "hours". It reflects the quality of the time of the product and is a reflection of the ability of the product to maintain its function for a specified period of time. Specifically, it refers to the average working time between two adjacent failures, also known as the mean time between failures.

The life of a display is the working time required when the brightness of the display reaches 50% of its initial brightness.

For example, the average trouble-free time of a company's display screen is 10,000 hours, and the life of the display screen is 100,000 hours.

IP protection level

According to the International Electrotechnical Commission standard IEC529-598 and the national standard GB7000-96, according to the degree of protection against foreign objects and water intrusion is classified such as IP65, where the first digit corresponds to the level 6 in (1), indicating complete dustproof. The second digit corresponds to level 5 in (2), which means to prevent water spray from entering, and so on.

Use ambient temperature

The display ambient temperature is a physical quantity that indicates how hot or cold the environment is. The working environment temperature of our display screen: -20~50 °C, the best working temperature is room temperature 20 °C. For outdoor screens, it is generally required to install air conditioning to make the display work in a more suitable temperature range and extend the service life of the display.?

Use ambient humidity

A physical quantity that indicates the degree of dryness of the atmosphere, the less water vapor contained in a certain volume of air at a certain temperature, the drier the air; The more water vapor, the more humid the air. The degree of dryness and wetness of the air is called "humidity", in this sense, it is often expressed by physical quantities such as absolute humidity, relative humidity, comparative humidity, poor mixing ratio saturation and dew point; If the weight of liquid moisture in wet steam as a percentage of the total weight of steam is expressed, it is called the humidity of steam. The working relative degree of our display is: 10%-90%.