What is LED backlighting? Types of lighting. LED TV

LED backlighting of displays is one of the many ways to use LEDs. It has been used on an industrial scale since 2008. Today, LEDs are installed in the vast majority of liquid crystal (LCD) screens: TVs, monitors, and mobile devices.

Since 2008, LED backlighting has been actively improved and improved. In this article we’ll talk about what LED backlighting is, what it comes in, and how justified its implementation in electronics is.

A little theory

Just 10 years ago, the main light source in LCD screens were CCFL and HCFL fluorescent lamps, which were inferior to plasma TVs in image quality. The advent of white SMD light-emitting diodes with high luminous efficiency, low power consumption and dimensions has radically changed the situation, thanks to which a new generation of monitors has appeared.

Stores began to actively offer LED TV, without explaining that only LED backlighting was used, and the screen still remained liquid crystal. Large-scale advertising campaigns and beautiful stories from consultants about the advantages of the LED option have contributed to a sharp increase in sales of LED TVs and monitors, thanks to which today they have complete superiority over other types of backlighting.

LED Backlight Types

With the invention of compact ultra-bright LEDs, manufacturers were faced with the question: “How to place them in order to simultaneously obtain an image high quality and save money? Several types have appeared in search of an answer LED backlight, among which there are two main ones:

• end (Edge), also called side or edge;
• matrix (Direct), assembled on wled or rgb led.

According to the method of controlling the glow, there are also two types of backlight: static and dynamic. In the first case, the brightness of all LEDs changes equally regardless of the image. In the second case, each LED or group individually interacts with the corresponding section of the LCD matrix.

Edge

LEDs in the side lighting are arranged in one of the following ways:

• on the sides;
• above and below;
• along the perimeter.

The choice of one or another placement method depends on the screen size and production technology. This type of backlight uses only white LEDs. The light flux they emit passes through the diffuser and the light guide system, thus illuminating the entire screen.

This method has three important advantages that made it popular. Low cost achieved due to the minimum number of LEDs used and the simplicity of the control system. The ability to create ultra-thin monitor models with a remote power supply, which, due to advertising, have become very popular among buyers. Low energy consumption, which is impossible to achieve in other variations. By light edge characteristics the backlight occupies an average position and strongly depends on the build quality and the used element base. But in general, color rendition is comparable to CCFL technology. Edge-lit TV models cannot achieve high contrast images for two reasons. All LEDs shine with the same brightness, equally illuminating dark and light areas of the screen. Light guides, despite their well-thought-out design, are not able to ensure uniform distribution of light over the entire working surface.

Direct

The back (matrix) illumination is a matrix assembled from several lines with LEDs distributed over the entire area. This method ensures uniform illumination of the entire LCD panel, and most importantly allows for dynamic control. As a result, the developers managed to achieve high image contrast and rich black color.

Direct backlighting is implemented in two ways. The first, most common, is assembled using white LEDs or WLEDs, which are basically the same thing. It can be either static or dynamic, depending on the TV model.

The second one suggests using instead of white - RGB LEDs. With their help, it is possible to adjust not only the brightness, but also set any color from the entire visible spectrum. Due to high speed switching LEDs perfectly process the supplied signal and keep up with the rapidly changing picture on the screen. RGB lighting is built only according to the dynamic principle.

Matrix-backlit displays feature excellent contrast and color rendition across the entire screen area. This is their main advantage, which is covered by several disadvantages, namely:

• high cost;
• high power consumption comparable to CCFL technology;
• The case thickness is more than one inch.

If one of the LEDs fails, the entire line goes out. This phenomenon will be reflected on the screen as a darkening of a certain area. You won’t be able to replace a burnt-out element with a similar one yourself, since you can’t find exact copy with the same lens it is almost impossible. As a result, the entire line must be replaced.

About health disadvantages

LED backlight itself, regardless of its implementation method, has several significant drawbacks that affect not the image quality, but the vision. First of all, this is a pulse-width modulation function. With its help, the user adjusts the brightness and, thereby, worsens his health. The essence of the problem is the flickering of LEDs with a frequency above 80 Hz, which manifests itself when the brightness is reduced. Such flickering is not visually detected by the human eye, but it continuously irritates the nerve endings, causing headaches and fatigue in the eyes.

While watching television this disadvantage does not cause much discomfort due to the large distance between the viewer and the screen, as well as low concentration of attention. But users of PCs and laptops with LED backlighting find themselves in a dead end situation. On the one hand, when the monitor brightness is 100%, the pulse width modulation (PWM) function is disabled, but the retina of the eye suffers greatly. On the other side, long work with documents at reduced brightness it is more comfortable for the eyes, but now PWM adds negativity.

In addition, there are other shortcomings that impair vision, the manifestation of which to one degree or another depends on the display production technology. For example, increased radiation of LEDs in the region close to the ultraviolet spectrum.

Those who value their eyesight should opt for a professional series of monitors with CCFL lamps, which are still produced for working with images. They have a high color rendering index and cost less than RGB LED products.

Despite the presence of shortcomings, manufacturers of electronic equipment will not stop using LED backlighting in their devices, and large companies So-called LED TV will continue to be advertised. Because marketing goals still have a high priority. We can only hope that in the near future mass production of monitors will be equipped with higher quality backlighting, operating at a frequency that is safe for the eyes.

Read also

LED TVs have gained particular popularity among users due to their characteristics and quality. However, not everyone understands what an LED TV is, how it differs from others and how it works. this technology. Therefore, today we decided to talk about the advantages and disadvantages of this technology, as well as answer other questions.

In television equipment, LED means a liquid crystal LCD TV backlit by edge or direct light-emitting diodes. Older TV models used cold cathode lamp backlighting. Thanks to new backlight technology, image quality has improved, which means brightness, contrast, color depth and color rendition itself have improved.

To create such a monitor with edge backlighting, we use large number small individual LEDs. In this case, each of the diodes is responsible for illuminating a specific area of ​​the screen. This technology allows you to reduce the thickness of the TV. In addition, unlike fluorescent lamps, which are used in LSD TVs, LEDs, used in both direct and edge backlighting, last much longer.

Features of LED backlight

In fact, most of the parameters in ice TV depend on the quality used. It affects parameters such as:

• Contrast;
• Brightness;
• Viewing angle;
• Black Level;
• Color gamut;
• Color rendering;
• Response time;
• Update rate.

An increase in screen contrast led to the emergence of such a thing as dynamic contrast. This means that the brightness of each diode when illuminated direct type regulated separately from other areas. The static contrast does not change, since it depends on the display matrix.

In addition, in ice TV with backlighting of both direct and edge types, new technology local dimming, which provides local dimming, thanks to which groups of LEDs can be controlled. This darkening method is quite popular, however, it has some disadvantages.

1. The color is not uniform, so you can notice dark and bright spots where there is no backlight or it is turned on very brightly.
2. Fine image details disappear in dark areas.
3. At the junctions contrasting colors colored halos appear.

However, do not worry, since they are not visible in a regular picture.

Types of ice backlight

The backlight in such screens is divided into several main types:

• Direct – diodes of blue, red and green colors are located evenly from the back of the matrix, forming a screen. With direct technology, you can achieve the most optimal color coverage and ensure best quality color transfer. However, it is worth noting that displays with direct technology consume more electricity and have greater thickness.
• Edge – white LEDs along with a diffusion panel are located around the perimeter of the screen. Edge TVs more energy efficient and thinner, but achieving good local dimming is difficult. Edge backlighting is the most popular, especially in TVs with a small diagonal.

Composite LEDs

Direct backlighting on TVs differs from classic RGB LED. Composite LEDs of three colors began to be used in order to improve the color gamut. However, the required color gamut was not achieved, since there was often too little of it. Therefore, based on this technology, other light diodes were invented to achieve desired result. So, today quantum dots or diodes GB-R LED and RB-G LED are used in ice TV.

In GB-R technology, blue and green LEDs are combined into one, coated with a red phosphor, and in RB-G, red and blue are combined, which is ultimately coated with a green phosphor.

Disadvantages and advantages of LED TVs

As a result, it can be noted that such TVs have a large number of advantages, and among the disadvantages, in fact, only the “biting” price.

In this article we will look at what it is LED technology and where it is applied. I’ll say right away that not only the matrices of monitors and televisions (), but also anything from the bottom of a car to tap water are illuminated. Now let's talk about this in more detail.

Generally speaking, an LCD monitor is a device that consists of just a few basic components. This is a pixel matrix, backlight and top protective layer. In this case, the image itself is generated by a matrix of pixels, but since it does not emit light at all, it has to be illuminated from behind. You can shine a flashlight from the front, but it’s unlikely that anyone will sit and shine it into the monitor while working;) A backlight is used for this.

Previously, in older models of LCD monitors, it was electroluminescent, that is, a tube with gas, as in lamps for lighting schools, offices, and so on. It is clear that in monitors and televisions such lamps are much smaller, and the gas is different, but the main operating principle is the same. Now, most new models use LED backlighting, that is, LEDs (light-emitting diodes).

When using lamps, they are installed around the perimeter of the screen, and to distribute the light evenly from the perimeter to the center, reflectors and light-diffusing filters are used.

When using LED backlighting, two options are possible. The first is traditional, cheap and practical - the same installation around the perimeter. In this case, everything is done in the same way as with lamps - diodes are installed around the perimeter and their light is carried to the center by reflectors and various filters. But, naturally, there will be no improvement in the quality (uniformity) of illumination compared to electroluminescent lamps. But, however, there are advantages! Reducing energy consumption when using LED backlighting is reduced several times. As, in fact, the release of heat.

All of the above applies to the budget - white backlight (although it is actually blue, additional yellow filters are simply used). It is installed on the sides for the same purpose - saving money. Such monitors sell out faster because they do not scare away consumers with their prices. But there is another option for installing the backlight - over the entire surface of the matrix. It is much more uniform and of better quality, and besides, it is also colored. Yes, this is the so-called RGB LED backlight. It consists of RGB LEDs in three colors: red, green and blue. Located over the entire area of ​​the matrix, such a backlight can be turned off to obtain an absolutely black color on the screen, and can be illuminated a certain color, giving the picture brightness and color saturation.

However, since the cells can be quite large, when complete shutdown parts of the backlight to obtain black color, the part of the image that should be bright may also be affected. But, most likely, this will all be solved simply by increasing the number of LED cells or even controlling individual diodes yourself, it will just take more computing power central processor at the monitor.

LED lighting throughout

In fact, backlighting can be used anywhere. For example, I have selected for you some successful, in my opinion, pictures with diodes.

LED bike lighting

Sofa with lighting

As you can see, everything depends only on imagination. LED lighting is perfect for cars, bicycles, furniture and even showers or faucets. Turn out to be enough interesting effects and your hands start to itch to do something like that, well, go ahead! Don't hold back :)

In 2016, the development of television technology brought LED-backlit TVs to the peak of popularity; they are called “ice TVs.” Also today in stores you will find television receivers with OLED-based screens.

LED TVs are television receivers in which the screen is built on a liquid crystal matrix (LCD) backlit by LEDs.

The liquid crystal matrix is ​​abbreviated in English as “LCD” (liquid crystal display). And previously, devices with such screens were called LCD TVs. But for the liquid crystal screen to work, it needs a backlight, and for the first few years a CCFL fluorescent lamp was used for backlighting. Then light-emitting diodes (LEDs) began to be used to operate the backlight. And now TVs with liquid crystal displays are called “LED TVs”, which is the same as “LCD TVs”. The differences in these names are only in the form of backlighting; all other parameters and operating principles remain the same.

In 2014, all companies stopped producing LCD TVs with illumination from a fluorescent lamp. Models are available with liquid crystal screens and LED backlighting. And today such television receivers constitute the most widespread and affordable segment of televisions. Plasma models are already leaving the market, there are only a few companies left that continue production plasma TVs and these are just a few new models in 2014, and these are not flagship models. But the devices with OLED screens(screens based on light-emitting LEDs) refer specifically to flagship models, and their price does not yet allow these TVs to become mass-produced.

Differences between LED and conventional LCD

When using lamps to backlight the matrices, it was impossible to adjust the backlight of individual areas of the screen. This led to the fact that the contrast of LCD screens was not high enough to compete with plasma or even picture tubes that were still alive at that time. Therefore, we came to the decision to use LEDs to illuminate the matrix. At the same time, it became possible to adjust the backlight by separate areas, adjusting the brightness of individual LEDs.

This is where we get advantages of LED backlight Compared to a conventional fluorescent lamp:

• improved screen brightness,
• contrast,
• color rendering,
• and energy consumption has decreased by up to 40%.

Differences in backlighting between CCFL and LED

LED lighting methods

There are two types of LED backlight: side and back. Side (Edge) lighting, in which LEDs are located around the perimeter of the TV body. Backlight (Direct) illumination, in which the LEDs are located evenly behind the matrix. Best results The image quality is provided by Direct backlighting with the ability to locally dim groups of LEDs. Edge backlighting is cheaper, so it is more used in TV production

The main problem of LCD screens was contrast, or rather its low value. Contrast is the ratio of the brightness in the brightest area of ​​the screen to the brightness in the darkest area. Screen manufacturers have tried to adjust the backlight brightness in different areas to increase contrast. That's why it appeared local dimming technology, which allows you to control groups of several LEDs at once. The local dimming system has several disadvantages. Firstly, poor color uniformity (bright and dark spots are noticeable) in areas where the backlight is brightly turned on and off. Secondly, colored halos appear at contrasting transitions. Thirdly, image details disappear in dark areas. But the increase in contrast and black level compensates for these shortcomings.

If we rank different technologies according to the indicator quality of the resulting picture, then you get the following result:

1. LED lighting using the Direct method;
2. LED lighting using the Edge method;
3. CCFL lamp backlight.

Today's models LED TVs have screen resolutions from HD Ready to Full HD, and this year there are also models with 4K Ultra HD resolution. LED models can also have functions such as 3D, Smart TV, a wide variety of connectors and other parameters. So every buyer among the models of LED TVs will be able to choose a suitable purchase for himself.