Outdoor led display as a vehicle for propaganda, we live in the frequent appearances, also will be increased demand for outdoor led display identification data with respect to maintenance. Here we how to identify brightness outdoor led display do some discussion. First, let's look at what led display brightness:
Brightness LED light tube is the luminous intensity of light emitted by the body, known as light intensity, expressed in MCD.
LED luminous screen brightness is a composite index, which means: all the LED module in the unit volume of the total luminous (luminous flux) with integrated indicators illuminance at a given distance.led display brightness: in a given direction, the luminous intensity per unit area on the brightness of the unit is cd / m2.LED brightness and the number per unit area, LED brightness proportional to itself. LED drive current is proportional to its brightness, but their life is inversely proportional to the square of the current, it is not too much in pursuit of improving the brightness of the drive current. In the same dot density, led display brightness depends upon the material of the LED chip, package and size, the larger the wafer, the higher the brightness; on the contrary, the lower the brightness.
So for ambient brightness Screen brightness which ask for?
General brightness requirements are as follows:
(1) Indoor LED Display:> 800CD / M2
(2) half indoor LED display:> 2000CD / M2
(3) Outdoor led display (northward):> 4000CD / M2
(4) Outdoor led display (facing south):> 8000CD / M2
The market sold the uneven quality of LED light tube, the brightness of the majority can not be guaranteed, the phenomenon of shoddy deceive consumers, most people do not have the ability to discriminate brightness LED light tube, therefore, merchants say how much the brightness is much brightness. And even with the naked eye is difficult to distinguish, so how to identify it?
First, how to identify brightness LED electronic display
1, make yourself an easy connection of light emitting diodes 3V DC power supply, preferably with battery production. You can use two button batteries, packed in a small plastic tube and leads to two probes as the positive and negative output, trailing by shrapnel made directly to a switch, the use of positive and negative probes corresponding to the light-emitting diodes are in contact negative pin, hold the end of the switch, the light-emitting tube was electric light.
2, followed by photosensitive resistor and a digital multimeter combined into a simple metering device, the photoresistor leads to two thin wires directly connected to a digital multimeter two tables pen multimeter on 20K gear position (depending on the light-sensitive resistors may be, try to make accurate readings), note that the measured value is actually sensitive resistor, so the smaller the value, the brighter the light.
3. Take a LED light-emitting diode, lit with more than 3V DC, is on the bald hair and live close to the connected photoresistor photosensitive surface, then, appears multimeter reading this resolution LED luminous brightness.
Second, the brightness discrimination level refers to the human eye can distinguish the image from the black to white between the brightness level.
LED electronic display of high gradation some can reach 256 or even 1024. However, due to the limited sensitivity of the human eye to brightness, and can not fully identify these gradation. That may be a lot of adjacent level gray eye looks the same. And the eyes ability to distinguish different person. For display, the human eye's natural level is better, because the displayed image after all posters. The human eye can distinguish brightness level, the greater the color space of the display means to display the rich colors of the greater potential. Brightness discrimination level can use special software to test generally able to display more than 20, even if the level is good.
Third, the brightness and viewing angle requirements:
Indoor full color LED display brightness to the 800cd / m2 or more, outdoor full color brightness to 1500cd / m2 or more, to ensure the normal operation of the display, or because the brightness is too low and can not see the displayed image. The size of the brightness of the LED die is good or bad decision. led directly determines the size of the viewing angle display the number of audience, and therefore the bigger the better. Perspective is mainly determined by the die package.
OK Brightness LED electronic display is very necessary, brightness requirements of the current city lighting led display, or the new regulations, the brightness of the LED screen is too high, it will cause problems for nearby residents. In order to avoid undesirable repercussions, which requires businesses to customize and maintain led display as needed with relevant expertise.
Two control LED brightness way:
One is to change the current flowing through the LED, the general LED tube allows continuous operating current of about 20 mA, there is in addition to the red LED saturation phenomenon, the other LED brightness is basically proportional to the current flowing through; Another method is to use the human visual inertia with a pulse width modulation method to achieve gray scale control, which is periodically changing the optical pulse width (ie duty cycle), as long as the repeated cycle of light short enough (ie, refresh rate high enough), people eye do not feel light-emitting pixels in the jitter. Since the pulse width modulation is more suitable for digital control, so in general the use of computer to provide the LED display today, almost all of the LED screen using pulse width modulation is used to control the gray level.
LED control system usually consists of three parts, the main control box, scan board and display and control device consists of:
Get a screen pixel control box from the computer graphics card in each color luminance data, and then re-allocated to a number of block scanning plate, each scan board responsible for controlling the number of rows (column) LED screen, and each row (column) on the LED display and control signals are transmitted in serial manner. There are two serial transmission of display control signals: one is the scan board centralized control of each pixel grayscale scanning plate from the control box brightness value of each pixel rows decomposition (i.e. pulse width modulation), then, each of the opening lines LED signals in pulses (1 lit, off to 0) by using serial transmission line to the corresponding LED on the control whether the light. This approach uses less components, but the larger the amount of the serial data transmission, because in a repeating cycle of light, each pixel requires 16 pulses at 16 gradation, 256 gradation in need 256 pulses, because the device operating frequency limit, generally only the LED screen to achieve 16 gray levels.
Another method is to scan the contents of each plate is not serial transmission but a switching signal LED 8 binary brightness value. Each LED has its own pulse width modulator to control the light time. Thus, in a repeating cycle of light, each pixel in the 16 gray only need four pulses, only 8 pulses at 256-level grayscale, greatly reduces the frequency of serial transmission. This method of using decentralized control LED grayscale can easily achieve 256 gray scale control.
Contact Person: Mr. Anheer Melton
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