How does LCD TVs work?


Nowadays, LCD (liquid crystal display) and Plasma technologies are the most widely used technologies in HD TVs. In fact, LCD technology is used all around us (Laptop screens, digital clocks, CD players …). In this article, we will explain briefly the key points of that technology and we will answer the question: how does an LCD TV work?

Let’s start with “liquid crystals” physically are. We learned in school that there are three states of matter: gases, liquids, and solids (crystals). So, the name "liquid crystal" sounds a little bit like a contradiction. In fact, as shown in figure1, molecules in Solids always maintain their orientation and stay in the same position with respect to one another. In liquids, molecules can change their orientation and move anywhere in the liquid. But there are some substances that can exist in an intermediate state where their molecules tend to maintain their orientation, like the molecules in a solid, but also move around to different positions, like the molecules in a liquid. This means that liquid crystals are neither a solid nor a liquid. That's how they ended up with their seemingly contradictory name.

Ok, let’s go back to TVs now. A TV screen is formed of hundreds of thousands of pixels [elementary small dots] (2 million pixels for the new 1080p HDTVs). Each pixel consists of 3 sub-pixels, each having at his end a Red, green, or blue filter. These sub-pixels are so small and close to each others that their colors will mix in human eyes.

LCD technology
LCD technology


In LCD TVs, a white light is provided at the back of the screen. If liquid crystals were not there , the white light will go through all pixel filters and will mix again at the output in each pixel  creating a white light (white screen). The role of the liquid crystals is “surprisingly” not to create light!!! But to remove undesirable parts of the light. For example, in a specific pixel, we want a purple color; the liquid crystal will block the light in the green sup-pixel, letting the blue and red going through. At the output, red and blue will mix creating a purple pixel.

We are almost set, the only thing left is: how does liquid crystals block the light? And the answer is quite easy. One of the optical proprieties of LQ is that they let through the light when they are aligned, and block it when they are not. So suppose 2 layers of liquid crystals and that one of them is fixed. By rotating the orientation of the second layer, we control the amount of light going through the layer.

Now, we have all the ingredients of the working process, let’s summarize and assemble all the parts together:

  •  A white light is provided on the back on the screen.
  • This white light is the input of all pixels and the sub-pixels they contain.
  • A built-in processor converts the video signal to a grid of data associating to every sub-pixel the amount of light to block.
  • This numerical data is converted to an electrical signal changing the orientation of the liquid crystal layer.
  • The 3 colors of light assemble out the pixel and mix to give a colorful pixel.
  • The full image is the created. 

Related posts :


How does Plasma TVs work?


The concept of plasma technology is quite simple, however to fully understand it, some background in physics is required. But, don’t worry, in this article, I will explain how does plasma TVs operate in a very simple way that everybody can understand.
The basic idea of plasma displays consists of illuminating hundreds of thousands of tiny colored fluorescent lights in the display screen to create a full image. Each tiny dot on the display (pixel) should be able to emit all the color levels. To do so, every pixel has 3 led’s (sources of light) Red, Green, and Blue. To have an idea about the exact number of pixels in the screen, you just need to check its resolution: 854 x 480 (ED TV’s) have 409,920 pixels; 1280 x720 (720p HDTVs) have 921,600 pixels; and 1920 x 1080 (1080p HDTVs) have 2,073,600 lightened pixels.

Till now, everything seems simple, but, the whole challenge is “how to lighten all these micro-lamps? And how to mix their 3 components (RGB) with the exact proportions to create any color? “


RGB color mixing



The answer is the following: each pixel in the display consists of 3 sub-cells (one for each color) full of xenon and neon gases sandwiched between the glass plates (figure 1).under each sub-cell, a phosphoric layer of the associated color is placed (Red , Green , or blue ). When the xenon and neon are not charged (natural conditions), the number of electrons (- charges) and protons (+ charges) are equal. But, when we introduce extra electrons to the cell, the gas become “ionized” and negatively charged. This is known in physics “plasma state” (state where gases are ionized) and this is from where the plasma TVs are called so. 

When any gas is ionized, it emits a certain amount of energy as a form of an electromagnetic wave in the ultraviolet spectrum (that we cannot see). When this electromagnetic wave hits the phosphoric layer, it shines with that color (R, G or B).



plasma technology
Plasma technology



To summarize, the process of creating the image in a plasma TV is as follows.


  •  Each and every gas sub-cell in the screen is charged (using electrical current ) with a specific intensity calculated by an embedded system
  •    When the cells are charged , the gas particles become ionized and emit an electromagnetic wave   in each sub-cell
  •     When this electromagnetic wave hits the phosphoric layer, the ladder shines with a specific intensity.
  •  The 3 sub-cells of each pixel are so close that a human being eye cannot discriminate the distances between them: their colors will mix to create a customizable micro-led in the screen.
  •   Combining the thousands of micro-led’s will give you a very clear picture quality.

Related posts :
  • How does a CTR TV work?
  • How does a 3D TV work?

LCD or plasma : what to choose ?


LCD or plasma
LCD Vs Plasma ;)

High definition and flat panel TV’s are taking out old fashioned tube TV’s and their poor picture quality at an amazing rate. More and more, people are replacing in their bulky TV’s for new LCD or Plasma screens. So, if you’ve made the decision to upgrade, which one should you go for: LCD or Plasma TV? This guide will walk you through all the key points and factors in determining which one to buy. First let’s talk about the similarities between the two



LCD & Plasma Similarities:

  • Thickness: both LCD’s and plasma’s are very thin monitors; each is only a few inches thick. You have the option to place them on a stand or mount them on a wall.


  •  Resolution:  they are both capable of similar picture performance, with bright, colorful, crystal-clear pictures, and high definition picture emission.


Despite these similarities, plasma and LCD display panels process the image in a completely different manner. More specifically, there is no relation what-so-ever between the LCD technology and plasma technology driving these displays. Here is a summary of the main advantages of each type

LCD advantages:

  • Screen Life: the screen life is estimated to be the number of hours before the picture starts fading. Plasma TVs have a screen life of 30,000 to 60,000 hours where as LCD TVs have more than 60,000 hours of viewing but this depends on the make and model of each TV.


  • Video gaming: if you are inclined toward video games then it is best that you choose an LCD TV as this does not have the problem of burn in and is much better for gaming.


  • Portability: LCD TVs are much lighter and thinner than Plasma TVs, so in case of portability, LCD TVs win hands down.


  • Energy Consumption: LCD monitors use very low amounts of power (1/2 ratio). This is why it is very commonly used in battery powered devices.


  • Screen burn-in: Plasma TV’s are more susceptible to screen burn-in where an image is “burnt” onto the screen when left on the screen too long such as a network logo in the bottom right corner of the screen.


  • glass cover:  Plasma TV’s require a panel of glass to cover it. This glass can reflect light and make it difficult to see the picture. If placed in a dark room, this typically isn’t an issue.


Plasma advantages:

  • Picture Quality:  where picture quality is concerned, Plasma TVs are much better than LCD screens but this doesn’t mean that LCD screen TVs are bad, in fact they are getting better every day.


  • Brightness:  Brightness levels aren’t as great as Plasma and it’s not possible to display darks quite as dark. Brightness and color are the major advantages of Plasma TV’s. They produce rich colors along with very deep blacks.


  • Viewing angle: Plasma TV’s viewing angle is also better as compared to the LCD TV, Their wide viewing angles allow more people to be able to watch TV comfortably. but the difference is not great enough to make a huge difference.


  • Price: Price is always a factor whenever you are buying any TV, but since Plasma TVs and LCD TVs are more technologically advanced the price plays a more important part in the final decision. Lets just say that price wise, an LCD TV is expensive than the Plasma TV but you can always compromise on size and fit your budget.


Summary

Some of these key points can help you in deciding which type of TV to purchase. Review your personal situation and determine which one is best for your household. Is your TV going to be in a room with lots if windows or light? If so, a LCD may be a better option due to the reduced glare. Are you looking for the best possible picture with the richest colors and darkest blacks? Then a plasma TV is probably the direction you want to go. 



Related posts :
Subscribe to: Posts (Atom)