What is an LCD TV?

Liquid crystal display (Liquid Crystal Display) is an organic compound with a regular molecular arrangement between solid and liquid. It is a transparent liquid state when heated, and a turbid solid state with crystal particles after cooling. substance.

LCD TV

1888

More and more LCD TVs have added dynamic contrast and natural light adjustment technology. In addition to improving the display effect of the picture, it also effectively improves the smearing phenomenon of the dynamic picture. In addition to improving the screen display effect, smart sound effects have also been added. With the addition of this technology, users can enjoy cinema-like audiovisual effects. More LCD TVs also have the product attributes of entertainment machines and have a good performance in terms of entertainment functions. In addition to playing mainstream video files, users can also browse information online and upgrade software through network connections. It fully meets the daily use needs of users.

"Father of OLED", Professor Deng Qingyun from the Hong Kong University of Science and Technology and Rochester University pointed out that due to the self-luminous nature, OLED can eliminate the need for backlights and other accessories compared to LCD liquid crystals. , Wearable, transparent and other characteristics. ^[1]

Tip 1: Try not to let the LCD TV work for a long time or keep displaying the same picture. Because the LCD TV screen is formed by the LCD pixel display, the LCD TV works for a long time, or the same picture is always overheating the LCD light-emitting tube and cause internal burnout. Therefore, when the user does not watch the TV, You should turn off the display or reduce the brightness of the display in time. Users should try to avoid pressing the Pause button to keep the screen displayed while enjoying the CD.

Tip two: Avoid hitting the screen. Because the LCD screen is very fragile, to avoid strong shocks and vibrations, users remind children not to practice impactful activities on the TV.

Tip 3: Pay attention to keeping the TV dry. TV sets have a high level of technology. Although they can work in humid environments, they can only work as usual, not "normal work." The moisture damage to the TV is great. Therefore, even if the user does not watch the TV for a long time, it is best to turn on the power periodically to let the heat generated by the monitor work to drive out the moisture in the machine.

Tip 4: Clean the screen properly. If the screen is dirty, it is best to use a professional cleaning agent to wipe it gently with a soft cloth dampened with a little water, but the amount of water should not be too large, because the screen short-circuits after entering the LCD. If fog is found on the LCD, it should be gently wiped off with a soft cloth before turning on the power. If moisture has entered the LCD, it must be placed in a drier, warmer place to allow the water to evaporate sufficiently.

Tip 5: Never disassemble the LCD yourself even when the power is not connected. Because of the long shutdown, the CFL converter in the TV's backlight assembly may still carry high voltages of about 1,000 volts. 1000 volts can also cause serious personal injury. In addition, even if the user is not overpowered, incorrect operation can cause temporary or even permanent damage to the display.

HDMI interface

When consumers buy an LCD TV, the following key indicators are the most important:

Resolution

The resolution of LCD TVs is fixed, unlike computer LCD monitors, which can be adjusted. The fixed resolution of the LCD TV is also its best resolution, and the high resolution can be easily compatible with HDTV. For any video signal that is not the optimal resolution of the LCD screen, the LCD TV needs to convert the image resolution before displaying the conversion. For LCD TVs, resolution is one of the important parameters. The resolution supported by traditional CRT TVs is more flexible, and the pixel pitch of LCD TVs is already fixed, so the supported display modes are not as many as CRT TVs. The best resolution of an LCD TV, also called the maximum resolution, is the only resolution at which an LCD TV can show the best image. LCD TVs mainly have several common resolutions such as 800 × 600, 1280 × 768, 1366 × 768, and 1920 × 1080.

Response time

The so-called "response time" is the response speed of the LCD screen to the input signal, that is, the response time of the liquid crystal from dark to bright or bright to dark. Obviously, the smaller the "Signal Response Time" indicator, the better. The smaller the response time is, the user will not have similar afterimage or dragging feeling when looking at the moving picture. Moreover, the requirements for liquid crystal televisions are higher than liquid crystal displays at this point.

Because computer monitors are generally used for static pictures such as text and pictures, the requirements for this indicator are not obvious. As the TV mainly plays activities and changing dynamic pictures, the shorter the signal response time, the better the display effect.

The data shows that the response time is 30 milliseconds, and the TV can display 33 frames per second, which is enough to meet the needs of DVD playback. The response time is 25 milliseconds, and the TV can display 40 frames per second, which fully meets the needs of DVD playback and most movies or games.

When we buy a TV, we must look at the TV picture from multiple angles. For example, we choose to face the screen from an angle, and then offset it by some angles. We must stand at the same level as the TV screen to see if we can see the image; When inspecting the machine, you can also let the promoters play some screens with fast speeds to see whether the screen shows consistent actions and whether the screen has tailing.

interface

When buying, don't just look at the surface, but also look at the interfaces on the back of the TV. These interfaces directly affect your "investment protection", so it is very important. For LCD TVs, the best interface standard is HDMI. This interface can simultaneously transmit audio and video signal digital interfaces, which not only simplifies the connection and reduces the connection burden, but also provides the bandwidth required for huge digital signal transmission. , Computers, home theaters and other equipment, will actively use this interface, apply this interface to connect with these devices, you can get the best results.

Considering that LCD TVs need to be connected to peripherals such as home theaters and computers, in addition to the necessary AV, S-Video and other interfaces, DVI and D-Sub interfaces, fiber optic output, etc. should also be considered within the scope of investigation.

Bad screen

The dead pixel problem is one of the biggest problems that plagues LCD TVs. The defective pixels on the LCD panel cannot be repaired. The LCD panel can only be replaced, and the LCD panel accounts for at least 70% of the cost of the entire LCD TV. Due to the limitation of manufacturing technology, it is inevitable that there will be dead spots, also known as "dead spots". The bad point may be a black point, or it may be a green or red point. We usually find it hard to find, but sometimes it's very annoying. Of course, after all, the liquid crystal manufacturing technology has not yet achieved a qualitative leap, so even large companies cannot guarantee that their LCD products will not have a bad point. Tips for identifying bad and bright points of LCD TVs: Consumers are better to test some monochrome pictures when buying, and then pay attention to pixels with abnormal colors. The easiest way is to make the screen completely black and see if there are bright spots in a piece of pure black. Then make the screen completely white and see if black spots appear. Finally change to red, green and blue to check the integrity of the color point. If you find that there are too many dead pixels during the inspection, do not buy.

Viewing angle

When viewing LCD TVs, there is also a problem of viewing angles, that is, when the viewing angle of human eyes and the display screen is greater than a certain angle, it may cause the screen display to be unclear and the reflectivity to be too large to see the screen clearly. Therefore, the larger the viewing angle, the more advantageous it is to watch TV pictures at various angles. The industry-recognized viewing angle is 160 degrees to 170 degrees from top to bottom and left to right. At this angle, the viewing needs of most occasions can be guaranteed. Some newly launched LCD TVs can reach a viewing angle of 176 degrees.

Brightness contrast

When people look at the screen, they hope that the higher the brightness and contrast, the better. Of course, the picture is more beautiful and the details are better. Many manufacturers have grasped this mentality of consumers, with nominal values of brightness and contrast. In fact, products with a brightness of 500 lumens and a contrast ratio of 600: 1 or more can fully meet the viewing needs. The best way is to feel it for yourself. In addition, the brightness uniformity of the screen is also very important, but it is usually not marked in the LCD TV product specifications. Whether the brightness is uniform or not is closely related to the number and configuration of the backlight and the reflector. A better-quality TV has a uniform brightness and no obvious bright areas. At this point, when the screen is switched to a black screen state, it is easier to capture the uneven brightness.

There are two ways to increase the brightness: one is to increase the light transmittance of the LCD panel; the other is to increase the brightness of the backlight source.

The mainstream brightness is above 250cd / m2, but highlight products are gradually becoming popular. Generally speaking, it is a high-brightness product when it reaches 400cd / m2 or higher. The high-brightness can make the displayed picture more clear and vivid, which is especially suitable for playing DVD movies.

As for the contrast, the mainstream products are between 400: 1 and 500: 1, and the difference is small, but there are also some high-end products that reach 800: 1 or more, so you don't need to pay too much attention when purchasing. Too high contrast, for example, above 400 will not have much practical significance, and the human eye can no longer distinguish.

The resolution will affect the sharpness of the picture. The LCD TV with high resolution is clear and delicate, and the edges of the picture are sharp and sharp. If the resolution is too low, the picture will be rough, and it will have a grainy texture in close view. Generally has the characteristics of high-definition television at a resolution of 1024 × 768 or above.

Screen type

LCD screens are divided into PC screens and dedicated AV screens due to different technologies and processes. The cost of ordinary PC screens is more than 1,000 yuan cheaper than the dedicated AV screens of the same size, and the performance is inferior. For reasons such as cost or difficulty in purchasing, there are individual manufacturers who charge inferiorly, which requires consumers to be extra vigilant, and to be especially careful about some particularly cheap LCD TVs.

Screen format

The ratio of the screen width to the height is called the screen ratio. LCD TV screen ratios are generally 4: 3 and 16: 9. 16: 9 is the most suitable format for human viewing angles and has a stronger visual impact. At the same time, the display format of digital television in the future will also adopt the 16: 9 format. 4: 3 is a suitable display format for analog TV signals, so if you mainly use it to watch TV, there are still certain advantages. It should be pointed out that many 16: 9 and 4: 3 format TVs can adjust the display format of the picture through the menu, but this is at the cost of wasting a certain area of the screen. If it is mainly used to watch TV, it is recommended to choose a 4: 3 product, otherwise the stretched picture will make you unbearable; and if it is mainly used to watch DVD movies, it is recommended to buy a 16: 9 product, because 16 : 9 will bring a visual enjoyment that 4: 3 will never reach.

Dot pitch

Point pitch generally refers to the distance between two adjacent pixels. Dot pitch is calculated by dividing panel size by resolution, but LCD TV dot pitch is far less important than CRT.

Reaction time

The so-called response time is the speed at which each pixel of the LCD TV responds to the input signal, that is, the time required for the pixel to change from dark to bright or from bright to dark? The principle is to apply a voltage to the liquid crystal molecules to twist and recover the liquid crystal molecules. 25ms and 16ms are often referred to as this reaction time. The shorter the reaction time, the less the user will feel the tail drag when watching the dynamic picture.

According to the data:

Response time 30ms = 1 / 0.030 = TV can display 33 frames per second, which can meet the needs of DVD playback;

Response time 25ms = 1 / 0.025 = TV can display 40 frames per second, which fully meets the needs of DVD playback and most movies or games.

Backlight life

The liquid crystal panel itself cannot emit light, and it belongs to a backlight-type display device. There is a backlight on the back of the LCD screen. The LCD TV relies on the LCD unit on the panel to "block" and "turn on" the light from the backlight to restore the picture.

It can be found that as long as the LCD monitor is powered on, the backlight starts to work. Even if the displayed picture is a completely black picture, the backlight will also remain in working state.

Since the light transmittance of the liquid crystal panel is extremely low, it is necessary to make the brightness of the liquid crystal television reach the level of restoring the picture. The brightness of the backlight should be at least 6000cd / m2. The life of the backlight is the life of the LCD TV. Generally, the backlight life of the LCD TV is more than 50,000 hours. In other words, if you use an LCD TV for an average of 5 hours a day, the lifespan of 50,000 hours is equivalent to 27 years of use of the LCD TV.

Receiving system

There are three main types of color televisions in the world, namely NTSC, PAL and SECAM. The three systems cannot be unified. China uses the PAL-D system, so the LCD TVs used in China must be at least compatible with the PAL-D system. Generally, LCD TVs are compatible with the above TV standards, but it is best to confirm before buying.

Sound output power

In order to make sound normally, LCD TVs have at least two built-in speakers, and its power determines the maximum sound intensity that the speakers can emit.

Since the main function of LCD TV is not to enjoy music, the power of sound is not very important. In contrast, the quality of sound may be more important. LCD TV speakers typically have a power of 2 to 10W.

Of course, if you need to connect an LCD TV to a home theater, then you will not bypass the power amplifier unit, so the sound output power of the LCD TV can be ignored.