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LED Display Screen Brightness

With more and more LED large screens placing on the streets, many people reflect that this has caused a lot of light pollution. In fact, it is not correct that light pollution is due to the LED display brightness setting. Today, we will talk about some detailed analysis of relevant knowledge of LED display screen brightness, we hope that this is useful.

One or two ways to control LED brightness:

One is to change the current flowing through the LED, the general LED tube to allow continuous operating current of 20 mA or so, in addition to red LED saturation phenomenon, the other LED brightness is basically proportional to the flow of current; Another method is to use The human eye of the visual inertia, with the pulse width modulation method to achieve gray-scale control, that is cyclically changing the pulse width (ie duty cycle), as long as the cycle of repeated light enough (ie, refresh rate is high enough) The eye is not feeling the shimmering pixels in the jitter. As the pulse width modulation is more suitable for digital control, so widely used in computers to provide LED display content today, almost all of the LED screen is to use pulse width modulation to control the gray level.

LED control system is usually controlled by the main control box, scanning board and display and control device composed of three major parts:

The main control box from the computer's graphics card to get a screen pixel brightness data of each color, and then re-assigned to a number of scanning plate, each scan board is responsible for controlling the LED screen on a number of rows (columns), and each row (column) On the LED display and control signals are transmitted in a serial manner. There are two serial transmission display control signal mode: one is the centralized control of the scanning plate pixel gray, the board will come from the control box of the pixels of the brightness value decomposition (ie, pulse width modulation) And then the LED on the line of the signal in the form of pulses (light is 1, not on the 0) for the use of serial transmission line to the corresponding LED, the control of its light. This approach uses fewer devices, but the amount of data transmitted serially is larger because each pixel requires 16 pulses at 16 levels of gray in a repeating lighting cycle, requiring 256 levels of grayscale 256 pulses, due to the device operating frequency limit, the general can only make LED screen 16 gray.

Another method is to scan the board serial transfer of the content of each LED is not a switch signal but an 8-bit binary brightness value. Each LED has its own pulse width modulator to control the lighting time. Thus, in a repeated light cycle, each pixel in the 16 gray level only need 4 pulses, 256 gray level only 8 pulses, greatly reducing the serial transmission frequency. With this decentralized method of controlling the gray-scale LED can be easily achieved 256-level gray-scale control.

Second, what is the brightness of led display:

LED luminous intensity of light emitted by the luminous intensity, known as the light intensity to MCD said. LED screen brightness is a comprehensive index, it refers to: all LED modules in the unit volume of the luminous flux (luminous flux) and a certain distance under the illumination of the composite indicators.

LED display brightness: in a given direction, the luminous intensity per unit area on the brightness of the unit is cd / m2.

Brightness and the number of LED per unit area, LED itself is proportional to the brightness. LED brightness and its drive current is proportional to, but life is inversely proportional to the square of its current, it is not in order to pursue the brightness of excessive increase in drive current. At the same density, LED display brightness depends on the LED chip used in the material, package and size, the larger the chip, the higher the brightness; the other hand, the lower the brightness.

Then the brightness of the screen for the body which brightness requirements?

General brightness requirements are as follows:

(1) indoor LED display:> 800CD/sq.m

(2) semi-indoor LED display:> 2000CD/sq.m

(3) outdoor led display (North and South):> 4000CD/sq.m

(4) outdoor led display (sitting south):> 8000CD/sq.m

The quality of the LED tubes sold in the market varies, the majority of brightness can not guarantee that shoddy phenomenon to deceive consumers, most people do not identify the ability of LED light tube brightness, therefore, the number of businesses that is the number of brightness brightness. And difficult to distinguish by the naked eye alone, then how to identify it?

Third, how to identify the brightness of LED electronic display

1, to make their own hands to connect a light-emitting diode 3V DC power supply, the best use of battery production. You can use two button batteries, installed in a small plastic tube and leads to two probes as positive and negative output, the tail with a shrapnel made directly into a switch, the use of positive and negative probes corresponding to contact the LED is positive Negative pin, hold down the end of the switch, the LED was electric light.

2, followed by photosensitive resistors and digital multimeter combined into a simple metering device, the photosensitive resistance leads to two thin wires, directly connected to the digital multimeter in the two table pen, the multimeter on the gear position 20K (depending on the photosensitive resistor, Try to make the reading accurate), note that the measured value is actually the resistance of the photosensitive resistor, so the brighter the light the smaller the value.

3, take an LED light-emitting diodes, with more than 3V DC light, light-emitting head is in close contact with the photosensitive surface of the connected photoresistor, this time, multimeter readings to distinguish between LED luminous brightness.

Fourth, the brightness discrimination level, refers to the human eye can distinguish the image from the darkest to the white between the brightness level.

LED electronic display gray level of some high, you can reach 256 or even 1024 level. But because the human eye sensitivity to brightness is limited, can not fully identify the gray level. Which means that a lot of adjacent grayscale grading may look the same. And the ability to distinguish between different eyes. For the display, the human eye to identify the level of nature is the better, because the display image is, after all, to see. The more the brightness level the human eye can tell, the greater the color space of the display means, the greater the potential for rich colors. Brightness level can be used to identify special software to test, the general display can reach 20 or more even if the level is better.

Fifth, the brightness and viewing angle requirements:

Indoor full-color LED display brightness to 800cd / m2 or more, outdoor full-color screen brightness to 1500cd / m2 or more, in order to ensure the normal work of the display, or because the brightness is too low to see the displayed image. Brightness of the size of the LED die is mainly determined by the good or bad. The size of the visual angle directly determine the number of led display audience, so the bigger the better. The viewing angle is primarily determined by the die package.

Determine the brightness of LED electronic display is very necessary, the current brightness of the city led the brightness of the display requirements, or a new requirement, LED screen brightness is too high, it will cause distress to nearby residents. In order to avoid adverse reactions, which requires businesses to customize and maintain the led display when you need to have the relevant professional knowledge.

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