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LED Dome Display Introduction

The appearance of the LED dome display is one of the products in response to people’s demand for novelty. Some years ago, if a large flat LED screen appeared in the square, people would be surprised: such a big TV set! Now, these „big televisions“ can no longer satisfy people’s curiosity. If one day an outdoor LED dome display with a diameter of 10 meters appears in the square, it will be a very popular product. Therefore, it is an unconventional and popular product. All defects caused by using a flat video source to play on a three-dimensional spherical surface will be tolerated, just as distorted photos taken by using a wide-angle mirror or a fish-eye camera will be accepted by people.

It is only in recent years that the LED dome display screen came into the market. A famous one is the LED dome display of Taiwan Pavilion of the 2010 World Expo. Up to now, three kinds of LED dome displays have appeared in the market. The manufacturing technologies of these LED dome displays have all been patented, and some have even applied for PCT international patents.

Today, let’s talk something in detail about it.

  1. How Many Types of LED Dome Display?
  2. “Watermelon Rind” LED Dome Display

The earliest dome display on the market, commonly known as the “Watermelon Rind” dome display, is composed of “Watermelon Rind” shape PCB. Its advantages are intuitive structure and fewer types of PCB, but its fatal disadvantage is that the north and south poles (i.e. north of 45 north latitude and south of 45 south latitude) cannot play images normally, so the picture utilization rate is too low, or the image deformation is serious. The reason is that the pixel arrangement of all image sources is in rows and columns at present, while the pixel arrangement of the north and south poles of the “Watermelon Rind” LED dome display is not in rows and columns, but in circles, so it is difficult to display.

 

  1. “Football” LED Dome Display

It composed of planar triangular shape PCB, commonly known as football screen, overcomes the defect that the south and north poles of “Watermelon Rind” LED dome display cannot play images, thus greatly improving the utilization rate of images. Its disadvantages are that there are many kinds of PCB, which is limited by the honeycomb arrangement of pixel points and cannot be too small, and software writing is also troublesome.

 

  1. Six-sided Panoramic LED Dome Display

It is a recently emerged LED dome display composed of quadrilateral PCB and is called a six-sided Panoramic LED dome display.  Its manufacturing method is also very simple. Take the manufacturing of a 1.5m diameter dome display as an example: divide the entire spherical surface into 6 surfaces with exactly the same shape and size, and then divide each surface into 4-unit boxes with exactly the same shape and size, summing up to 24 boxes in 6 surfaces. Each unit box consists of 16 flexible PCB with LED lights welded on the surface, and finally they are installed into a six-sided panoramic LED dome display.

 

There are fewer types of PCB boards for six-sided panoramic LED dome displays than football screens. Pixel layout is closer to the normal plane LED display screen, and the minimum dot spacing is also similar to that of the plane LED display screen. Therefore, the image sources that can be used for playing on the ordinary plane LED display screen can be directly played on the six-sided panoramic LED dome display, and the effect is much better than that of the dome display composed of watermelon-shaped PCB and triangular PCB. In terms of physical size, since the entire dome screen consists of 6 faces with identical shapes and sizes, each face consists of 4 unit boxes with identical shapes and sizes. They can be put into the air box, which is very convenient to disassemble and assemble and is convenient for the renter to use. In terms of software playing function, it can also play on the whole sphere with one video source, such as globe, like “Watermelon Rind” LED dome display. It can also play 6 different video sources or the same video source on 6 planes with the same size (i.e. upper, lower, left, right, front and rear 6 planes). Of course, different video sources can also be played individually or jointly through software. This is especially important for dome screens larger than 2 meters in diameter. Because a person’s height is less than 2 meters, his effective viewing angle is only about 1/6 of the surface of the dome.

 

  1. How is LED Dome Display Playing?

The playing principle of the LED display screen is that the control system of the LED display screen (controller+computer) transmits the image source played on the computer screen to the flat LED display screen for display.

 

Almost all the image sources in the world are planar. It is almost impossible to send the planar image sources to a three-dimensional LED dome display for display without processing. Fortunately, the dome is round. It is impossible for any individual spectator to see every corner of the LED screen at the same time. He can only see a small part of the surface of the dome. This is also related to the diameter of the dome screen. If the diameter of the dome screen is sufficiently large, the effective attention of the dome screen is only about one sixth of the surface area of the dome (due to the angle of view), of which five-sixths are invisible or not, because these five-sixths are respectively on the front and back of the dome, on the left and right sides, above and below. In this way, the following methods can be used: 1. Play six different image sources in six different areas of the sphere. 2. Play 3 different image sources in 3 areas of the sphere (e.g. left back, top right, front down). 3. Play 2 image sources in 2 areas (rear right front, top left bottom). Of course, it is also possible to play a plane image source on the whole sphere like a “Watermelon Rind” LED dome display.

 

The resolution design of the LED dome display is the same as that of the flat LED display screen, i.e. it is closely related to the viewing distance of the LED display screen. The general experience is P2.5, viewing beyond 2.5m, viewing beyond 6m of P6, if viewing is P20 outdoor screen, then viewing beyond 20m is also the same in actual use. This is a relatively vague choice and is qualitative rather than quantitative. Its basis is as follows:

 

The LED display screen is the same as the computer display screen. The images they display are all composed of image points, and each pixel point is composed of red, green, and blue color elements. There is a certain distance between pixels, which we call the dot spacing PH. The resolution of the computer display screen is 1024×768, with 1024 pixels in the horizontal direction and 768 pixels in the vertical direction. It is enough to display a fine enough image.

 

If the physical dimension of the computer display screen is 300mm in the vertical direction, then the pixel pitch on the computer display screen is PH =300/768 = 0.39 mm (as shown in Fig. 11).

 

PH is an important parameter of any digital display screen.

 

We have measured that the distance between human eyes and the computer display screen is D=450mm, then the included angle between two adjacent pixels and human eyes is θ.

 

Then there is equation θ = Arctg 0.39/450 (1)

If we place the computer display 30,000 000mm away from the operator and replace the computer display with an LED display or LED dome display, the distance from the human eye to the LED display or LED dome display is 30,000mm. Therefore, in order to ensure that the perceived amount of image pixels is constant (or the resolution is constant), the included angle of θ should also be constant. The only thing that needs to be changed is PH change.

 

According to equation (1), there is an equation: θ = Arctg 0.39/450 = ArctgPH/30,000+450, thus obtaining PH= 26 mm or so, i.e. we will design the pixel spacing of the LED dome display to be 15-20 mm, at which time the clarity of the dome display is sufficient and reasonable. At this time, the clarity of the LED screen image we saw from 30 meters away is the same as that we saw in front of the computer. If the distance between the person and the LED dome display is other, the PH value can be calculated by referring to the above method.

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