Tech

LCD vs LED: which technology is better?

Display technology continues its advance towards screens that are ever thinner, lighter and with realistic images. In this sense, LCD and LED systems have become the most popular, which is why when buying a 50-inch TV or any size we want to know which technology is better.

We currently live surrounded by screens: computer, tablet, mobile phone, 2 DIN radio  and television are some of the devices that consist of a screen to display text, still images and videos, however, the screens were not always as fine and practical as we know them today, which is why it is worth making a brief historical analysis of this technology.

Evolution of display technology

It all began at the end of the 19th century with the work carried out by the English chemist William Crookes, who laid the foundations for what is now called the cathode ray tube (CRT). However, it was the German scientist Carl Ferdinand Braun who consolidated the invention, creating the first oscilloscope. Later, this technology began to be used for the manufacture of televisions and monitors, first only in monochrome screens, but later also in color.

However, the cathode ray tube had three fundamental disadvantages; the devices were large and heavy, consumed a lot of energy and worked analogically, which is why in 1964 professors Donald Bitzer and H. Gene Slottow created the first plasma screen at the University of Illinois, which allowed students to work during long periods of time in front of the computer. Also, plasma screens were flat, thin, and flicker-free, so they quickly became an option for making televisions.

We can say that among the types of screens, plasma technology revolutionized the market, since both monitors and televisions stopped being big and heavy to become thin, elegant and lighter devices. This made it possible to manufacture large screens of up to 80 inches, very suitable for watching movies at home.

A plasma screen is made up of two crystals, one rear and one front. In the middle of them there are cells with neon and xenon gases, which are converted into plasma by applying electric current. This is how they begin to generate light in each pixel, creating a better contrast with more intense blacks. In addition, this technology is not affected by image refreshment, so you can reproduce action scenes without the typical trails that movements leave on other types of screens.

The arrival of the liquid crystal display (LCD)

Approximately 10 years after the appearance of the first plasma device, scientists at the David Sarnoff Research Center in New Jersey, in the United States, developed the technology called Liquid Crystal Display (LCD), known in Spanish as liquid crystal screen. It is an even thinner screen, made up of a reflective light and a large number of pixels placed in front of the light source.

To understand how an LCD screen works, it is necessary to think of it as a kind of sandwich, where the first slice is a light source made up of cold cathode fluorescent lamps, followed by a vertically polarized plate, a light diffuser, a TFT plate containing the transistors or pixels, a common transparent electrode, a color filter, another diffusing glass plate, and a horizontally polarized plate. 

By analyzing a pixel separately, we can see that this point of light is made up of 3 sub-pixels; one red, one green and one blue (RGB). If we get closer to one of them, we can see that the light comes from the fluorescent lamps, passes through the first polarizing filter and passes through the first glass plate that works as an electrode. Next, the light meets the liquid crystal molecules, which have a helical shape and thanks to the electric field, they rotate the light to take it to the second electrode and make it pass through the second polarizer, which is perpendicular to the first. This is a system known as normally white mode. If the electric field between the electrodes is not strong enough, the liquid crystal molecules will not have a helical shape, so the light will not be able to rotate, remaining dammed without being able to leave by the second polarizer. In this case, the subpixel looks black and is known as the normally black mode.

In other words, the liquid crystal molecules are found in each sub-pixel and thanks to the magnetic field between the electrodes they work as switches to turn the sub-pixels on and off, creating areas of different colors on the screen. But that’s not all, since the screens of the latest LCD TVs include a TFT plate, that is, an additional slice in the sandwich, which works with thin film transistors, in this way, it is possible to better control the amount of light passing through each subpixel. The result is an image that impresses with the detail created by millions of colors. 

LED: Improved LCD technology

When buying a television, it is common to have doubts about whether LCD or LED is better. However, the difference between LED and LCD is basically the lighting source. Thanks to the research of the North American engineer Nick Holonyak, the appearance of LED technology allowed a great improvement to be made to LCD screens, but in this case the explanation is very simple, it is exactly the same screen but with LED lamps instead of fluorescent lamps, therefore, it is not only kinder to the environment but also offers better image quality in terms of contrast and sharpness. 

OLED: The future of screens 

We cannot finish without mentioning this new way of manufacturing screens. Unlike the LED backlight that an LCD panel needs, OLED technology does not use any additional light source, since it works with a special type of diode with an electroluminescent layer, that is, it reacts to electrical stimulation by generating light itself. same. As if that were not enough, this allows making screens even thinner and even foldable.

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