TV Purchase Guide – Display Technology


TV Purchase Guide – Display Technology

In the previous articles we have considered the factors that affect the distance of the television position to the viewers such as resolution. These are the fundamental points that should be considered before purchasing a TV.

After the previous step, now it is time to know more about the technologies used in televisions, their comparison and their pros and cons. The main display technologies having been used are as follows:

  • CRT
  • LCD (LED is a derivative of LCDs as LED backlit LCD)
  • Plasma
  • OLED

In this article, we will explain more about CRT technology.

CRT stands for Cathode Ray Tube and these types of displays work as follows:

There is a vacuum tube that contains a phosphorescent surface and the images can be produced, when an electron beam hit the phosphorescent surface.

In this process the electron gun is responsible to produce the electron beams and the beams then will be accelerated to hit the screen.

Many devices and gadgets are now using the produced pictures with this method such as oscilloscope (in waveforms), pictures ( in televisions or monitors) and radars.

There is an important short form written as RGB that is being used in most of displays. RGB stands for Red, Green and Blue. And it means that every picture that is being shown on displays are created with these 3 colors.

But the question is that, how does it work and how 3 colors can create many colors and pictures?

In order to know better how CRT works, imagine that you want to paint a wall in purple color. The only colors that you have are green and blue. We know that if we mix green and blue together we can make a purple color and its final color depends on the proportion that we mix from green and blue. This is exactly how different colors and pictures are made in different displays.

Another thing that we should explain is that each electron gun generates one color. Therefore, in order to have RGB colors, we need 3 electron guns. That is, we need one electron gun for the red color, one for blue and one for green.

In this step, we have 3 main colors produced by electron gun to be emitted to the screen. The question is that how each of these individual beams can be guided to its correct position on the screen. Moreover, how they can be accelerated to hit the screen.

In order to achieve the two above task, we need other components in the vacuum tube.

First, we need Anodes to accelerate the electron beams.  Then, we need some coils called deflecting coins creating a low frequency magnetic field to guide and adjust the electron beam.

Since for adjustment of the beam we need to have access to change its direction horizontally and also vertically, therefore, we need two sets of deflecting coils. In this stage a small light spot can be seen on the screen when the electron beam hit the screen.

Now in order to produce a complete picture, a set of signals are applied to the system and the electron guns starts emitting electron beams constantly to the screen and by the guidance of deflecting coils, these beams hit the screens and they create spots from right to left and top to bottom.  The process of scanning systemically in sequence of horizontal linesis also called the raster.

The question is that how the human eyes see pictures instead of these light spots?

The answer is that these processes take place in such a fast way that the human eyes can not distinguish the time difference between each process and it sees in total a complete picture. If you want to understand it better, you can remember the game that we have played when we were younger. We draw multiple pictures in papers and each of the new picture with a tiny difference. When we start turn the pages rapidly, we see a moving animation. This is the example of how most of the displays show us images.

In the next articles we will explain about other display technologies and at the end we will compare these technologies with each other.

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