LCD

Technology LCD (stands for Liquid Crystal Displays via ABBREVIATIONFINDER) is not used only on monitors or TVs. On the market, it is possible to find portable devices – such as game consoles, cell phones, calculators and digital cameras – whose screens also make use of this technology. Laptops, for example, have used this type of screen for years.

As its name indicates, the “secret” of the LCD is in a material called liquid crystal, which receives its name because, although it is not exactly a liquid component, its characteristics make it act as such.

In their simplest constitution, liquid crystal molecules are distributed between two transparent polarized sheets called substrates. This process is oriented differently on the two blades, so that they form perpendicular polarizing axes, as if forming an angle of 90º. Roughly speaking, it is as if one blade receives horizontal polarization, and the other, vertical polarization, forming a “rows and columns” scheme.

Liquid crystal molecules are able to direct light. When an image is displayed on an LCD monitor, electrical elements present on the slides generate magnetic fields that induce the liquid crystal to “guide” the light coming from the light source to form the visual content. Whenever necessary, a different voltage can be applied, causing the liquid crystal molecules to change in order to prevent the passage of light.

In monochromatic screens (common in watches and calculators, for example), molecules assume two states: transparent (light passes) and opaque (light does not pass). For screens that display colors, different voltages and filters that work on white light are applied to the molecules.

LCD

Active and passive matrix

LCD screens are basically divided into two categories: active matrix (Active Matrix LCD) and passive matrix (Passive Matrix LCD). The first type has as main difference the application of transistors for each pixel (in a nutshell, pixel is a point that represents the smallest part of the image on a screen), whereas, in the passive matrix, transistors are applied based on the already mentioned scheme of rows and columns.

As a result, on active matrix screens, each pixel of the matrix can receive a different voltage, allowing, among others, the use of high resolutions. On the other hand, its manufacture is so complex that it is not uncommon to find new monitors that have pixels that do not work – the so-called “dead pixels”.

Passive matrix screens, in turn, have a simpler constitution. The liquid crystal is positioned between two substrates, as shown in the following illustration. Integrated circuits are in charge of controlling the loads that activate the pixels, allowing images to be formed on the screen.

Due to their simplicity, passive matrix screens are cheaper, but have considerable disadvantages, such as shorter response times (find out what this means later). Therefore, currently, its use is common only in devices that do not need as much quality, such as calculators. In this sense, more sophisticated equipment is built with an active matrix.

The simplicity of passive matrix screens lies in the fact that the application of stresses considering rows and columns does not have the same level of complexity as the manufacture of active matrix screens. The problem is that when a pixel is triggered from this scheme, applying voltage to it can cause the pixels of the neighboring rows and columns to be affected as well, causing them to work, even slightly, impairing the image generation as a whole.

In the active matrix, this problem was solved because the application of an individual voltage control for each pixel has no “side effect”, that is, it does not “contaminate” neighboring pixels. Generally, active matrix screens use a component called TFT (Thin Film Transistor – something like Transistor of Thin Film), whose main characteristic is precisely the application, through a layer, of specific transistors for each pixel.

LCD types

The search for better images combined with viable manufacturing processes has led the industry to develop several types of LCD. The following are the most popular varieties:

– TN (Twisted Nematic): this is one of the most common types, used in low-cost devices. In it, the liquid crystal particles are positioned in a twisted way. The application of electric charge is able to make the crystals rotate up to 90 degrees, according to the voltage level used, determining whether or not light passes. There is also a type called STN (Super TWisted Nematic) that is a kind of evolution of TN. Its molecules have improved movement, making it possible for the user to see the monitor image satisfactorily at angles many times greater than 160º, a characteristic that does not exist in TN panels. There are still other variations, such as Double Layer STN and Film compensated STN ;

– IPS (In-Plane Switching): this is a more sophisticated technology, applied mainly to higher quality LCD equipment. In it, the liquid crystal particles follow a horizontal rather than a vertical alignment, as usually happens with TN panels. Thanks to this, IPS screens are able to work with a higher update rate (concept discussed later), resulting in more visual comfort for the user. IPS panels also offer more sharpness and brilliance, in addition to satisfactory viewing even when the screen is viewed from a side point. There is also a variation called S-IPS (Super IPS), capable of working with more angles, higher resolutions and higher brightness rates. As they use more energy – a consequence mainly of using larger quantities of transistors – IPS screens are not often used in portable devices, such as laptops and tablets;

– AFFS (Advanced Fringe Field Switching): similar to IPS technology, since it also uses horizontal alignment, the AFFS specification is used in equipment that offers high image quality, having as differentials the ability to present a good visualization in different angles of observation and to offer excellent color fidelity;

– VA (Vertical Alignment): in this type, the liquid crystal particles are in a vertical position in relation to the substrates. Such screens are capable of offering good color reproduction and viewing at various angles, but generally have a response time at worse levels compared to IPS and AFFS. As with other types, VA screens also have variations, the most common being MVA (Multi-domain Vertical Alignment) and PVA (Patterned Vertical Alignment);

– ASV (Advanced Super View): this is a technology developed by Sharp that resembles VA. According to the company, its main advantage is the support for various viewing angles, which can reach 170 degrees. This is because liquid crystal molecules are able to position themselves in various directions, with movements similar to those that fireworks make when exploding;

– Super PSL (Plane-to-Line Switching): being one of the most recent and having Samsung behind its development, PSL technology is similar to the IPS standard. However, according to the company, a type screen is about 10% brighter and has a 15% lower manufacturing cost compared to the latter. Its application is intended for monitors and TV sets as well as for mobile devices.

 

What is Plasma?

LCD technology is certainly a great step forward for the display industry (displays), but did not come alone: mainly in television sets segment, screens Plasma account for a good share of the market.

In fact, it is not necessarily a new technology: the first screens of this type were introduced in the 1960s. However, the technology has only undergone significant improvements in recent years.

As you already know, the main component of the LCD is the liquid crystal present between two slides. In Plasma, the scheme is similar, but the material that remains between the layers is a type of gas that is stored in a set of millions of cells.

This gas, when electrically stimulated, releases ultraviolet light. This, in turn, causes a reaction in the phosphorus atoms that line each cell. Phosphorus is an element that generates illumination when subjected to another light.

In Plasma panels, each pixel is usually made up of three cells, each responsible for a different color: red (red), green (green) and blue (blue). The combination of these generates the colors we see on the screen. The phosphor present in each cell receives a different intensity of ultraviolet light, enabling millions of combinations that result in the color gamut.

Thanks to this, Plasma panels can have their pixels individually illuminated. The result is a screen with excellent levels of brightness and sharpness, even when viewed from positions further away from the front of the device.

 

Which is better: LCD or Plasma?

It depends. It may seem like a very elusive answer, but it is the most appropriate. It is good to know that each technology has its advantages and disadvantages, and that these can be mitigated or enhanced, depending on the product as a whole.

By default, we can say that the LCD has the following disadvantages: less brightness, does not display a “deep” black color with fidelity, possibility of one or more pixels not working correctly (the aforementioned dead pixel), there may be more limitations in the variety of available resolutions, among others.

Plasma screens, in turn, are susceptible to a problem called burn-in, which consists of marks left on the panel when certain images are displayed for a long time on the device, such as the logo of a TV station in the corner of the screen. In addition, they are more expensive and often more fragile.

But, as you saw in the topic on LCD types, the industry works tirelessly on ways to improve technologies, so it is not uncommon for problems associated with each standard to be mitigated or even eliminated.

For this reason, faced with the dilemma of choosing between an LCD product and a Plasma product, it is certainly more appropriate to observe the specifications of each device. The following topic addresses the most common features.

 

Screen features

When choosing a video monitor or even a TV, regardless of the technology, it is important to observe some aspects to make a good acquisition. Below are the main characteristics to be observed.

Response time

The response time is an important feature, especially those who want to use the monitor or TV for games or high-definition video. That’s because these are applications that require quick changes to the visual content. If the monitor or TV is not able to keep up with these changes, that is, it has a bad response time, it will cause unwanted effects, such as “ghost objects” in the image or shadow in movement.

The shorter the response time, the better the image update. For current standards, it is recommended a device that has this measurement in less than 10 ms.

Refresh rate

The refresh rate (rate refresh) indicates the number of times the screen is refreshed per second. Its measurement is made in Hertz (Hz). If a monitor works at 75 Hz, for example, it means that the image is refreshed 75 times per second on the screen.

In general terms, the higher the refresh rate, the more visual comfort the user will have, especially in very busy video sequences. The recommended minimum is 60 Hz.

It is worth noting, however, that this aspect was very important in CRT devices, since they use a beam of light that sweeps across the screen. Thus, the higher its refresh rate, the faster the beam ends one scan and begins another.

In current screens, whether they are LCD, Plasma or OLED, the refresh rate is not that important, since the pixels remain active until a change in image causes them to change their condition.

Screen size and resolution

When LCD monitors started to become popular, it was common to find screens with sizes of 14, 15 and 17 inches. Today, the most common minimum size for monitors is 19 inches, and it is not uncommon for monitors with screens of 20, 21, 23 or even more inches. The most common TVs vary between 20 and 50 inches, with Plasma screens generally being applied more commonly on larger models.

It is also interesting to note that, today, virtually all monitors and televisions are of the widescreen type . This indicates that your screens are wider, making them an excellent option for viewing movies or for displaying more information on the screen.

As a rule, a monitor can be considered widescreen when it has an aspect ratio greater than 4: 3. This means that the aspect ratio of the screen is one unit of measure greater in width for every three units of measure in height. For comparative purposes, a screen with an aspect ratio of 4: 4 (or 1: 1) would be sufficient to be considered square.

It is worth noting that if a screen has, for example, a 19-inch size and a widescreen format, this does not mean that the device is necessarily larger than a “normal” 19-inch monitor. What happens on widescreen screens is that, roughly speaking, their sides are further apart, but the distance between the upper and lower ends does not increase in the same proportion.

Regarding the resolution, monitors and televisions currently work with satisfactory rates. When we talk about this aspect, we are referring to the set of pixels that form horizontal and vertical lines on the screen. Let’s take a resolution of 1600×900 as an example.

Still on resolution, you can find terms like 720p and 1080p. As this article on HDMI explains, these nomenclatures indicate the number of pixels supported by the device, in addition to the use of progressive scan or interlaced scan . In progressive scan, all pixel lines on the screen are updated simultaneously. In turn, in interlaced scan mode, first the even lines are updated and then the odd lines, that is, it is a “line yes, no line” scheme. In general, progressive scan mode offers better image quality.

Therefore, the letter ‘p’ in 720p, 1080p and other resolutions indicates that the mode used is progressive scan. If interlaced scan is used, the letter applied is ‘i’ (for example, 1080i). The number, in turn, indicates the number of vertical pixel lines. This means that 1080p resolution, for example, has 1080 vertical lines and works with progressive scan. Here are some common resolutions:

  • 480i = 640×480 pixels with interlaced scan;
  • 480p = 640×480 pixels with progressive scan;
  • 720i = 1280×720 pixels with interlaced scan;
  • 720p = 1280×720 pixels with progressive scan;
  • 1080i = 1920×1080 pixels with interlaced scan;
  • 1080p = 1920×1080 pixels with progressive scan.

You may have heard of the term Full HD (High Definition) . This expression, whose interpretation would be something like “Maximum High Definition”, indicates that the screen works at the maximum resolution, which is 1080p. This means that the device will be able to play videos in maximum quality – from a Blu-ray disc, for example – prepared for this level of resolution.

More sophisticated televisions capable of working with 4K are appearing on the market, a resolution so high that its use is not uncommon in cinemas. This measure indicates that the device is capable of providing images up to 4096×2160 pixels. Incredible, isn’t it? To get an idea of ​​the “power” of 4K resolution, a video of a few seconds may require several gigabytes in size to take advantage of its full potential.

It is also possible to find equipment that works with resolutions of 2K (2048×1080 pixels) and 8K (7680×4320 pixels).

Contrast and brightness

The contrast is another important feature when choosing monitors and televisions. This is a measurement of the difference in brightness between the strongest white and the darkest black. The higher this value, the more faithful the image colors display. This is because this rate, when in greater numbers, indicates that the screen is capable of representing more differences between colors. For minimum fidelity, it is recommended to use screens with a contrast of at least 500: 1 or, if the manufacturer reports this measurement as being “dynamic contrast”, 10,000: 1.

Regarding brightness, the ideal is to use screens that have this rate at least 250 cd / m² (candela per square meter).

Viewing angle

The easiest way to view the content displayed on the screen is to be right in front of it. But, in the living room of a house with several people, for example, someone will always be in a lateral position in relation to the TV. That is why it is important to choose a monitor or a TV with support for more “generous” viewing angles .

Ideally, choose a device that offers the maximum viewing angle as close as possible to 180 degrees. Note that some manufacturers may advertise this measure as, for example, 170H / 150V. The letter ‘H’ indicates the angle horizontally, while ‘V’ does so considering the vertical, that is, the view from so many degrees up and down.