Today we will talk about LED backlights in LED TVs. Let's discuss the reasons for their failure and where to buy LEDs.

Preface

The backlighting of the first LCD TVs was made using fluorescent ( CCFL) lamps This backlight has proven itself to be the best, however, it is in many ways inferior to LEDs in terms of brightness, backlight dynamics and energy consumption.

If a powerful inverter is needed to ignite CCFL lamps, then for LEDs a small driver is needed, the main function of which will be to control the current and voltage to power the LEDs.

The main causes of failures of LED TV backlights.

While they have many advantages, LEDs are not without their disadvantages. Increasingly, TVs from well-known brands such as LG or Samsung are being sent for repairs because the LED backlight burns out. Sometimes, the fault of the backlight failure is not the LEDs themselves, but also the improper operation of the TVs. For myself, I identify three reasons for the failure of LEDs.

First reason- this is a miscalculation of the manufacturers themselves. When repairing LED backlights, very often you encounter a situation where, when measuring the current flowing through the LEDs, it turns out that it is too high. For example, in backlight strips, where the maximum current should be about 250 mA, in fact we get about 400-450 mA. Naturally, with such a current, the TV produces a bright picture, but the LEDs quickly burn out. After replacing the LEDs with new ones, you have to reduce the current, thereby saving the TV from repeated repairs, and the owner of the equipment from repeated costs.

The second reason- defective LED. As with any spare parts, from time to time you can get a defective part. In my practice, I came across cases when only one LED burned out, and the rest were in perfect order. Looking through all the LEDs under a microscope for cracks and measuring the current consumption, I did not find any faults. Everything turned out to be normal. Having replaced just one LED, the TV was sent to the owner, after which it continued to serve him faithfully.

Third reason- Constantly watching TV at maximum brightness. This operating mode also affects the durability of the backlight. I recommend always watching TV at a backlight level of no more than 70-75%, as this significantly increases the service life of TVs.

Where is the best place to buy LEDs for repairs?

I used to buy LEDs at the radio market, but recently they have become prohibitively expensive there. After that, on the advice of knowledgeable craftsmen, I buy only from trusted sellers on Aliexpress. Replacing the LED backlights of TV matrices is not very difficult, you can see how I do it in.

Replacing LEDs using a stove table is described

I attach a list of LEDs that I bought below.

Photo	Name	Purchase link
	LEDs 2 W 6 volts on LG size 3535 (large anode pad (+))
	LEDs 6 volts on LG 1 W size 7030
	LEDs 3 volts on LG 0.5 W size 7020
	LEDs 3 volts on LG size 3528 (large anode pad (+))
	LEDs 3 volts on Samsung 1 W size 3537
	3 volt LEDs for Samsung size 7032
	LEDs 3 volts on Samsung 0.5 W size 5630
	LEDs 3535 2 watts 6 volts on LG (large platform cathode (-))

Television manufacturers regularly introduce users to new technologies that improve image quality. Approaches to combining TV screens and LED elements have long been mastered by major companies. Recently, the source of bright and soft glow is also moving to the displays of mobile devices. Users of traditional LED-based lighting can also appreciate the advantages of this solution, but, of course, the backlight of LED screens on TVs looks most attractive. Moreover, it is complemented by other high-tech inclusions used by the developers of this technology.

Backlight device

When creating modules to implement backlighting, LED arrays are used, which can consist of white LED elements or multi-colored ones, such as RGB. The design of the board for equipping the matrix is ​​specially designed for the purpose of integrating a specific media model into the device. As a rule, on the left side of the board there are contact connectors, one of which provides power to the LED backlight, and the others are designed to control its operating settings. A special driver is also used, the function of which is interfaced with the controller.

In its finished form, it is a row of miniature lamps that are connected in groups of 3 pieces. Of course, manufacturers do not recommend interfering with the design of such tapes, but if desired, you can physically shorten or, conversely, make the device longer. Also, the standard backlight of the LED screen provides the ability to adjust the brightness, supports soft start and is equipped with voltage protection.

Classification of lighting by installation type

There are two ways to integrate LED backlighting - direct and edge. The first configuration assumes that the array will be located behind the LCD panel. The second option allows you to create very thin screen panels and is called Edge-LED. In this case, the tapes are placed around the perimeter of the inside of the display. In this case, the uniform distribution of LEDs is carried out using a separate panel, which is located behind the liquid crystal display - usually this type of LED screen backlight is used when developing mobile devices. Adherents of direct illumination point to the high-quality result of the glow, which is achieved thanks to a larger number of LEDs, as well as local dimming to reduce color stains.

Application of LED backlight

The average consumer can find this technology in TV models from Sony, LG and Samsung, as well as in products from Kodak and Nokia. Of course, LEDs have become more widespread, but it is in the models of these manufacturers that qualitative shifts towards improving the consumer qualities of this solution are observed. One of the main tasks that faced the designers was to maintain the performance of the screen with optimal characteristics in conditions of direct exposure to sunlight. Also recently it has improved in terms of increasing contrast. If we talk about advances in screen design, there are noticeable reductions in panel thickness, as well as compatibility with large diagonals. But there are still unsolved problems. LEDs are not able to fully reveal their capabilities in the process of displaying information. However, this did not prevent LED technology from displacing CCFL lamps and successfully competing with the new generation of plasma screens.

Stereoscopic effects

LED-based modules have many capabilities to provide various effects. At this stage of technology development, manufacturers are actively using two stereoscopic solutions. The first provides for angular deflection of radiation fluxes with support for the diffraction effect. The user can perceive this effect while viewing with or without glasses, that is, in holography mode. The second effect involves a shift in the light flux, which is emitted by the backlight of the LED screen in the direction of a given trajectory in the liquid crystal layers. This technology can be used in combination with 2D and 3D formats after appropriate conversion or recoding. However, regarding the possibilities of combination with three-dimensional images for LED backlights, not everything is smooth.

3D Compatible

This is not to say that LED-backlit screens have serious problems interacting with the 3D format, but for optimal perception of such a “picture” by the viewer, special glasses are required. One of the most promising areas of this development is stereo glasses. For example, several years ago nVidia engineers released shutter 3D glasses with liquid crystal glass. To deflect light flows, the LED backlight of the LCD screen involves the use of polarization filters. In this case, glasses are made without a special frame, in the form of a ribbon. The built-in lens consists of a wide array of translucent ones that perceive information from the control device.

Benefits of backlighting

Compared to other backlighting options, LEDs significantly improve the consumer quality of television screens. First of all, the immediate characteristics of the image are improved - this is expressed in increased contrast and color rendition. The highest quality processing of the color spectrum is provided by the RGB matrix. In addition, the backlight of the LED screen has reduced power consumption. Moreover, in some cases, a reduction in electricity consumption of up to 40% is achieved. It is also worth noting the possibility of producing ultra-thin screens that are lightweight.

Flaws

Users of TVs with LED backlighting have criticized them for the harmful effects of blue-violet radiation on the eyes. Also, bluish tint is observed in the “picture” itself, which distorts the natural color rendition. True, in the latest versions of high-resolution TVs, the LED backlight of the screen has practically no such defects. But there are problems with brightness control, which involves pulse width modulation. During such adjustments, you may notice screen flickering.

Conclusion

Today, the segment of TV models with LED technology is in its infancy. The consumer is still assessing the capabilities and advantages that an innovative solution can provide. It should be noted that the operational disadvantages that LED backlight has do not confuse users as much as the high cost. Many experts consider this factor to be the main barrier to the widespread popularization of the technology. However, the prospects for LEDs still remain promising, since their costs will decrease as demand increases. At the same time, other lighting qualities are also being improved, which further increases the attractiveness of this proposal.

Models of LED-backlit TVs dominate the market and deservedly so. In this article we will look at the types of LED backlights on modern TVs and evaluate their effectiveness.

LED TVs

Let's start with the fact that LED TV is not a new type of HDTV . Unlike plasma and OLED TVs, which are made on the basis of emitting technologies, where each pixel is a separate light source, in liquid crystal models, each pixel of the LCD matrix requires lighting (from behind or from the side through a lens system). So LED HDTV models are the same liquid crystal (LCD or LCD) TVs, but they have a built-in light-emitting diode (LED) backlight, which replaces the standard cold cathode fluorescent lamp (abbreviated CCFL).

2 types of LED backlight according to design: matrix and side

LED backlighting with local dimming. First, televisions with LED backlight, used to illuminate the cells of the LCD matrix " full array"(full array) of LEDs, similar to standard TVs based on backlighting using CCFL lamps. But to change the thickness of TVs downward, the developers abandoned the use of a full array of LEDs behind the screen, installing lines of light sources on the side of the LCD panel. Thus, the distribution of light from LED sources over the entire screen area is carried out using specially shaped LEDs. These LCD TV models are called TV with side or regional LED backlight, which still dominate today.

LED lighting with local dimming system allows you to automatically reduce the brightness or completely turn off individual groups of backlight sources. Most modern LCD TVs with LED backlighting are equipped with a full array of LED sources placed behind the LCD panel. dynamic backlight technology also called local or local dimming. Using local dimming, specific areas of the overall backlight LED array become darker or lighter depending on the brightness and color of the corresponding part of the image on the screen.

The ability to darken a specific area of ​​the screen can reduce the amount of light that passes through the closed pixels of the LCD panel, which has a positive effect on the rendering of blacks, which become darker and more realistic. Because black levels are critical to contrast, the perception of depth on black surfaces, full-color images become more vibrant and clear. Local dimming technology has the only drawback - the effect of local dimming, which is formed when part of the light from brighter zones leaks into neighboring darker ones, which subsequently lightens the dark color at the border. It is quite difficult to notice the clouding effect on most models, since the disadvantage is directly related to the number of local dimming zones behind the screen, and manufacturers do not always provide such information.

When using standard backlighting using CCFL lamps and in most LCD TVs with edge LED backlighting, all backlight sources brighten or dim at the same time (the so-called " global dimming"), but among TV models from Samsung and LG there are rarely displays with side LED backlighting, which can also work on the principle of local dimming (“precision dimming” for Samsung and “LED Plus” for LG). To put it simply, this is a local dimming sham.

Thin models with side LED backlight Of course, they suffer from uneven screen illumination, but not everyone. Main feature of TVs with side LED backlighting– a thin body, therefore it is difficult to ensure uniform distribution of the light flux over the entire plane of the screen. When purchasing a TV, play an image of the white surface on the edge-lit LED display screen to check that there are no brighter areas around the edges of the screen. Likewise, when the screen is filled with a black field, the edges should not appear lighter (gray).

It is also worth noting that LED backlighting, regardless of the type, does not improve the viewing angles of the LCD panel. The black level drops when using LED backlighting and possibly shifting the viewing angle by 1-2 meters to the left or right.

We must not forget about the energy efficiency of LED backlighting. Of course, the consumption of any model is significantly affected by the size of the screen and the brightness of the backlight sources. LCD TV models of both types of LED backlighting are much more energy efficient compared to plasma models.

LED backlights for LCD displays are divided into categories according to the following criteria:

• glow color: white or RGB;
• lighting uniformity: static or dynamic;
• design: matrix or side (this is described in more detail above)

RGB backlighting is used to fine-tune the light spectrum. In addition, additional compensation for changes in the emission spectrum of LEDs over time is often applied. LED TVs with RGB LED backlighting light up different areas of the screen depending on the color of the image. Colored backlighting provides enhanced contrast and deep blacks, as demonstrated by many Sony LED TVs.

Edge LED: Better Color Rendering

Sony in its new flagship TV models - for example, the W905 line - uses Triluminos technology. The LED backlight (Edge LED) built into the frame of the TV on all sides of the screen is complemented by so-called quantum dots - fragments of a semiconductor several hundred atoms in size that emit light in a strictly specified range. Triluminos technology is designed to minimize color distortion and provide enhanced red and green tones. This will allow you to achieve an extremely uniform and natural image with a significantly wider color gamut. Tests of the first devices with Triluminos support did not disappoint us: the color gamut of the Sony KDL-46W905A model is comparable to that of organic light-emitting diode (OLED) solutions and is unattainable for LED-backlit LCD TVs. The W805 and W605 series devices, which also went on sale this year, do not use Triluminos, making their cost significantly lower. In the future, manufacturers will be able to completely abandon LED backlighting in favor of quantum dots.

OLED TVs: brightness and color at their best

TVs with OLED screens have already reached stores, and developers have rushed to release new models with concave displays. Last year, LG planned to introduce a 55-inch OLED TV to the market, but it only went on sale this summer. In Russia, model 55EM9600 and its improved analogue 55EM9700 will cost the buyer 500,000 rubles. In addition, the device is sold in Europe, the USA and some other countries.

Advantages of OLED TVs: it is not a type of backlight, but a different technology

• accurate color reproduction
• greater brightness margin compared to other technologies
• high contrast compared to LCD models (another imaging technology).
• absence of an LCD matrix and LED backlight - their place was taken by a matrix made of light-emitting organic diodes.

Samsung and LG independently developed OLED TVs with concave screens (Curved OLED). This design is designed to minimize distortion at the edges of the image and increase detail. New items are still available in limited quantities in South Korea, the USA and some European countries. The 55-inch model Samsung KN55S9C is priced by the manufacturer at $9,000 (300,000 rubles).

Of particular interest is also Multi-View technology, implemented in many models of OLED TVs with both flat and concave screens. Due to their extremely fast response time, such devices allow you to simultaneously show two or four programs in high definition (Full HD) or two different films in 3D format. Shutter glasses are used to separate the image. Each viewer can use the controls located on the glasses to select an individual program for viewing. At the same time, thanks to the built-in headphones, playback of the soundtrack corresponding to the film is ensured.

LED backlighting in modern TVs with liquid crystal screens today has several technological solutions. In an effort to increase the color gamut to better display colors, TV display manufacturers have developed new backlighting methods that differ from conventional LEDs.

RGB LED

To obtain a wide spectrum of white light, they began to use triads of LEDs consisting of blue, green and red colors in the backlight.

It was an alternative to WLED with a white LED and a smaller color gamut. The lighting system with three different LEDs is called RGB LED. The color gamut of RGB-backlit screens was greater than those using only white LEDs or using a CCFL fluorescent lamp. But there were also disadvantages: price, size, weight, different aging times for LEDs of different colors, which over time led to image color detuning. Therefore, we abandoned RGB LED backlighting in favor of WLED.

RGB LED

WLED

Given the shortcomings of RGB backlighting, TV manufacturers have settled on using “white” LEDs. They are located either on the sides of the case or in one array behind the LCD matrix. With the help of special diffusers, the light from the diodes is evenly distributed across the entire screen.

Although we call these LEDs “white,” they actually emit blue light, which passes through a yellow filter and is converted to white. Therefore, the use of white LEDs in screens back in 2010 gave a bluish tint to the image.

Over time, manufacturers have improved the components, and the WLED backlight has become quite functional, but as far as the light spectrum is concerned, some imbalances in the display of colors are noticeable.

Light spectrum from WLED

This peak in blue is due to the blue LED. Using a filter you can get white light. And this filtered light hits the red, blue and green subpixels to form the entire spectrum of the limited color gamut. Passing through filters, part of the spectrum is lost, and the flux intensity at the frequency corresponding to blue will be greater than at red and green. Screen calibration can help you get the correct colors, but these reasons allow the WLED-backlit screen to display colors in only sRGB space.

sRGB color space

If a WLED display displays colors in the picture that are close to blue (shades of blue), then the advantage in the spectrum of the blue color may put pressure on other colors that will be mixed to create a tint. Therefore, shades close to blue may not be displayed correctly.

There was a similar problem when using a CCFL lamp, but there the problem was with the green color. It was in green that the peak intensity was visible.

Light spectrum from CCFL backlight

Increased color gamut

To expand the color gamut beyond sRGB and move to the next color standard, changes were made to the WLED backlight.

And after the changes they began to use the name GB-R LED or GB-r LED. Now, instead of a white LED, a combined blue and green LED coated with a red phosphor is used.

This technology allows you to get peaks in the spectrum in red, green and blue.

Light spectrum from GB-r LED

This technology is used today in LG on AH-IPS matrices and in Samsung on PLS. Using GB-r LED technology, you can achieve 99% Adobe RGB coverage.

Some manufacturers use a different method to increase the color gamut in their screens. They take a mixture of blue and red LEDs and use a green phosphor for the filter. This technology is called RB-LED or RB-G LED.

LCD backlight

LCD backlight- a set of components that illuminate the matrix in LCD displays. Used to improve low-light readability in small displays, as well as computer monitors and LCD TVs.

The LCD displays of many portable devices are not backlit, so they require illumination from external light sources. However, most modern displays contain built-in backlighting.

The backlight itself consists of the following components:

• directly the light source (for example, a fluorescent lamp);
• a diffuser that provides uniform illumination of the entire display;
• inverter, which converts voltages and also controls brightness;

Types of light sources

• Miniature incandescent lamps;
• Cold cathode fluorescent lamp (CCFL);
• Hot cathode fluorescent lamp (HCFL);
• External electrode fluorescent lamp (EEFL);
• Single LEDs;
• LED matrix;

Monochrome displays usually have a yellow, green, blue or white backlight, while color displays usually have a white backlight.

Application

Small, cheap LCD panels typically use color LED backlighting, although recently white LED backlighting has become increasingly common. Large-area displays often use backlighting on electroluminescent panels, either colored or white. Most computer displays use cold cathode fluorescent lamps (CCFLs).

LED lights

LED backlights for LCD displays are divided into categories according to the following criteria:

• glow color: white or RGB;
• lighting uniformity: static or dynamic;
• design: matrix or side.

RGB backlighting is used, as a rule, to fine-tune the light spectrum. In addition, additional compensation for changes in the emission spectrum of LEDs over time is often applied.

If the brightness of the matrix backlight is adjusted equally over the entire area, the backlight is called static. If it is possible to control the illumination of individual parts of the matrix (usually depending on the scene), the illumination is called dynamic.

Depending on the design, the LED backlight can be side-mounted, that is, installed on the sides of the panel instead of conventional backlights, thus requiring a diffuser, or behind the LCD matrix. In the latter case, the LEDs are organized into a matrix of one resolution or another, possibly with individual control.

Screen flickering

If the backlight brightness is controlled by pulse width modulation, the screen flickers subtly. This can be checked by shaking a pen or pencil against the background of the screen. If the frequency is too low, the silhouette of the handle will split into several (stroboscopic effect). People who are sensitive to flicker experience tired eyes and may experience migraines.

Links

Notes

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See what “LCD display backlighting” is in other dictionaries:

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A transflective liquid crystal display (monitor) is a liquid crystal display that both reflects light and emits it (glows on its own). The term is derived from the English words “pass” and “reflect” (transflective ... Wikipedia