What is LED backlighting on a TV? LED TV: are there any disadvantages? LED backlighting varies

LED display backlighting is one of the many ways to use LEDs. It began to be 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, resulting in the emergence of a new generation of monitors.

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? In search of an answer, several types of LED backlight have appeared, 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. In terms of light characteristics, edge lighting occupies an average position and strongly depends on the build quality and the element base used. 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 you to implement 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 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. It will not be possible to replace a burnt-out element with a similar one on your own, since it is almost impossible to find an exact copy with the same lens. 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 lies in 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 any particular discomfort due to long distance between the viewer and the screen, as well as low concentration. 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 function pulse width modulation(PWM) is disabled, but the retina suffers greatly. On the other side, long work with documents for reduced brightness It’s 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 electronic technology will not stop using LED backlighting in their devices, and large companies will continue to advertise so-called LED TV. Because marketing goals still have 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.

Disassembling the monitor

Many articles have already been written on the topic of disassembling a monitor; all monitors are very similar to each other, so in brief:
1. Unscrew the monitor delivery mount and the only bolt at the bottom that holds the back wall of the case

2. At the bottom of the case there are two grooves between the front and back of the case, insert a flat-head screwdriver into one of them and begin to remove the cover from the latches along the entire perimeter of the monitor (simply turning the screwdriver carefully around its axis and thereby lifting the case cover). There is no need to exert excessive effort, but it is difficult to remove the case from the latches only the first time (during the repair I opened it many times, so the latches became much easier to remove over time).
3. We have a view of the installation of the internal metal frame in the front of the case:

We take out the board with the buttons from the latches, take out (in my case) the speaker connector and, bending the two latches at the bottom, take out the inner metal case.
4. On the left you can see 4 wires connecting the backlight lamps. We take them out by squeezing them slightly, because... To prevent it from falling out, the connector is made in the form of a small clothespin. We also remove the wide cable going to the matrix (at the top of the monitor), squeezing its connector on the sides (since the connector has side latches, although this is not obvious at first glance at the connector):

5. Now you need to disassemble the “sandwich” containing the matrix itself and the backlight:

There are latches along the perimeter that can be opened by lightly prying with the same flat screwdriver. First, the metal frame holding the matrix is removed, after which you can unscrew three small bolts (a regular Phillips screwdriver will not work due to their miniature size, you will need a particularly small one) holding the matrix control board and the matrix can be removed (it is best to place the monitor on a hard surface, such as a table covered with the fabric facing down, unscrewing the control board, place it on the table, unfolding it through the end of the monitor, and simply lift the backlit case, lifting it vertically up, and the matrix will remain lying on the table. It can be covered with something so that it does not gather dust, and assembled exactly. reverse order- i.e. cover the matrix lying on the table with the assembled case with backlight, wrap the cable through the end to the control board and, screwing the control board, carefully lift the assembled unit).
The matrix is obtained separately:

And the backlit block separately:

The backlit block is disassembled in the same way, only instead of a metal frame, the backlight is held plastic frame, which simultaneously positions the plexiglass used to diffuse the backlight light. Most of the latches are located on the sides and are similar to those that held the metal frame of the matrix (they open by prying them off with a flat-head screwdriver), but on the sides there are several latches that open “inward” (you need to press on them with a screwdriver so that the latches go inside the case).
At first I remembered the position of all the parts to be removed, but then it turned out that it would not be possible to assemble them “wrongly” and even if the parts look absolutely symmetrical, the distances between the latches on different sides of the metal frame and the locking protrusions on the sides of the plastic frame holding the backlight will not allow them to be assembled “wrongly.” "
That's all - we disassembled the monitor.

LED strip lighting

At first, it was decided to make the backlight from an LED strip with white LEDs 3528 - 120 LEDs per meter. The first thing that turned out to be is that the width of the tape is 9 mm, and the width of the backlight lamps (and the seat for the tape) is 7 mm (in fact, there are backlight lamps of two standards - 9 mm and 7 mm, but in my case they were 7 mm). Therefore, after examining the tape, it was decided to cut 1 mm from each edge of the tape, because this did not affect the conductive paths on the front part of the tape (and on the back, along the entire tape, there are two wide power cores, which will not lose their properties due to a decrease of 1 mm over a backlight length of 475 mm, since the current will be small). No sooner said than done:

Just as neat led strip trimmed along the entire length (the photo shows an example of what happened before and what happened after trimming).
We will need two strips of 475 mm tape (19 segments of 3 LEDs per strip).
I wanted the monitor backlight to work the same way as the standard one (i.e. it was turned on and off by the monitor controller), but I wanted to adjust the brightness “manually”, as on old CRT monitors, because this is a frequently used function and climb on OSD menu I got tired of pressing several keys every time (on my monitor, the right-left keys do not adjust the monitor modes, but the volume of the built-in speakers, so the modes had to be changed through the menu every time). To do this, I found a manual for my monitor online (for those who need it, it’s attached at the end of the article) and on the page with Power Board According to the diagram, +12V, On, Dim and GND are found that interest us.

On - signal from the control board to turn on the backlight (+5V)
Dim - PWM backlight brightness control
+12V turned out to be far from 12, but somewhere around 16V without backlight load and somewhere around 13.67V with load
It was also decided not to make any PWM adjustments to the backlight brightness, but to power the backlight with direct current (at the same time, the issue is resolved that on some monitors the PWM backlight operates at a not very high frequency and for some this makes their eyes a little more tired). In my monitor, the “native” PWM frequency was 240 Hz.
Further on the board we found contacts to which the On signal is supplied (marked in red) and +12V to the inverter unit (the jumper that must be removed to de-energize the inverter unit is marked in green). (photo can be enlarged to see notes):

The LM2941 linear regulator was used as the basis for the control circuit, mainly because at a current of up to 1A it had a separate On/Off control pin, which was supposed to be used to control the backlight on/off with the On signal from the monitor control board. True, in LM2941 this signal is inverted (that is, there is voltage at the output when the On/Off input is zero potential), so we had to assemble an inverter on one transistor to match the direct On signal from the control board and the inverted input of LM2941. The scheme does not contain any other excesses:

The output voltage for LM2941 is calculated using the formula:

Vout = Vref * (R1+R2)/R1

Where Vref = 1.275V, R1 in the formula corresponds to R1 in the diagram, and R2 in the formula corresponds to a pair of resistors RV1+RV2 in the diagram (two resistors were introduced for smoother brightness adjustment and reducing the range of voltages regulated by the variable resistor RV1).
I took 1kOhm as R1, and the selection of R2 is carried out according to the formula:

R2=R1*(Vout/Vref-1)

The maximum voltage we need for the tape is 13V (I took a little more than the nominal 12V so as not to lose brightness, and the tape will survive such a slight overvoltage). Those. maximum value R2 = 1000*(13/1.275-1) = 9.91 kOhm. The minimum voltage at which the tape still glows at least somehow is about 7 volts, i.e. minimum value R2 = 1000*(7/1.275-1) = 4.49 kOhm. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer resistor RV2. The resistance of RV1 is 9.91 kOhm - 4.49 kOhm = 5.42 kOhm (we select the closest value of RV1 - 5.1 kOhm), and RV2 is set to approximately 9.91-5.1 = 4.81 kOhm (in fact, it is best to first assemble the circuit, set the maximum resistance of RV1 and measure the voltage at At the output of LM2941, set the resistance RV2 so that the output has the required maximum voltage (in our case, about 13V).

Installation of LED strip

Since after cutting the tape by 1 mm, the power conductors were exposed at the ends of the tape, I pasted electrical tape (unfortunately, not blue but black) onto the body in the place where the tape will be glued. The tape is glued on top (it is good to warm the surface with a hairdryer, because the tape sticks much better to a warm surface):

Next, the back film, plexiglass and light filters that lay on top of the plexiglass are mounted. Along the edges I supported the tape with pieces of eraser (so that the edges on the tape did not come off):

After that, the backlight unit is assembled in the reverse order, the matrix is installed in place, and the backlight wires are brought out.
The circuit was assembled on a breadboard (due to simplicity, I decided not to wire the board), it was attached with bolts through holes in the rear wall metal case monitor:

Power and control signal On were supplied from the power supply board:

The estimated power allocated to the LM2941 is calculated using the formula:

Pd = (Vin-Vout)*Iout +Vin*Ignd

For my case, it is Pd = (13.6-13)*0.7 +13.6*0.006 = 0.5 Watt, so it was decided to make do with the smallest radiator for the LM2941 (placed through a dielectric pad since it is not isolated from the ground in the LM2941).
The final assembly showed that the design was fully functional:

Among the advantages:

Uses standard LED strip
Simple control board

Disadvantages:

Insufficient backlight brightness in bright daylight (the monitor is placed in front of a window)
The LEDs in the strip are not spaced closely enough, so small cones of light from each individual LED are visible near the top and bottom edges of the monitor
The white balance is a little off and goes slightly greenish (most likely this can be solved by adjusting the white balance of either the monitor itself or the video card)

Quite a good, simple and budget option for repairing the backlight. It’s quite comfortable to watch movies or use the monitor as a kitchen TV, but it’s probably not suitable for everyday work.

Adjusting brightness using PWM

For those Habro residents who, unlike me, do not remember with nostalgia the analogue brightness and contrast control knobs on the old ones CRT monitors You can make control from the standard PWM generated by the monitor control board without bringing any additional controls outside (without drilling the monitor body). To do this, it is enough to assemble an AND-NOT circuit on two transistors at the On/Off input of the regulator and remove the brightness control at the output (set the output voltage to constant 12-13V). Modified scheme:

The resistance of the trimming resistor RV2 for a voltage of 13V should be around 9.9 kOhm (but it is better to set it exactly when the regulator is on)

More dense LED backlight

To solve the problem of insufficient brightness (and at the same time uniformity) of the backlight, it was decided to install more LEDs and more often. Since it turned out that buying LEDs individually is more expensive than buying 1.5 meters of strip and desoldering them from there, a more economical option was chosen (desoldering LEDs from the strip).
The 3528 LEDs themselves are placed on 4 strips 6 mm wide and 238 mm long, 3 LEDs in series in 15 parallel assemblies on each of the 4 strips (the layout of the boards for the LEDs is included). After soldering the LEDs and wires, the following is obtained:

The strips are laid in twos at the top and bottom with wires to the edge of the monitor at the joint in the center:

The nominal voltage on the LEDs is 3.5V (range from 3.2 to 3.8 V), so an assembly of 3 series LEDs should be powered with a voltage of about 10.5V. So the controller parameters need to be recalculated:

The maximum voltage we need for the tape is 10.5V. Those. maximum value R2 = 1000*(10.5/1.275-1) = 7.23 kOhm. The minimum voltage at which the LED assembly still glows at least somehow is about 4.5 volts, i.e. minimum value R2 = 1000*(4.5/1.275-1) = 2.53 kOhm. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer resistor RV2. Resistance RV1 is 7.23 kOhm - 2.53 kOhm = 4.7 kOhm, and RV2 is set to approximately 7.23-4.7 = 2.53 kOhm and adjusted to assembled circuit to obtain 10.5V at the output of the LM2941 when maximum resistance RV1.
One and a half times more LEDs consume 1.2A of current (nominally), so the power dissipation on the LM2941 will be equal to Pd = (13.6-10.5)*1.2 +13.6*0.006 = 3.8 Watt, which already requires a more solid heatsink for heat removal:

We collect, connect, we get much better:

Advantages:

Quite high brightness (possibly comparable, and perhaps even superior to the brightness of the old CCTL backlight)
The absence of light cones at the edges of the monitor from individual LEDs (LEDs are located quite often and the backlight is uniform)
Still simple and cheap board management

Flaws:

The issue with the white balance, which goes into greenish tones, has not been resolved
LM2941, although with a large heatsink, gets hot and heats everything inside the case

Control board based on step-down regulator

To eliminate the heating problem, it was decided to assemble a brightness controller based on a Step-down voltage regulator (in my case, an LM2576 with a current of up to 3A was chosen). It also has an inverted On/Off control input, so for matching there is the same inverter on one transistor:

Coil L1 affects the efficiency of the converter and should be 100-220 µH for a load current of about 1.2-3A. The output voltage is calculated using the formula:

Vout=Vref*(1+R2/R1)

Where Vref = 1.23V. For a given R1, you can obtain R2 using the formula:

R2=R1*(Vout/Vref-1)

In calculations, R1 is equivalent to R4 in the circuit, and R2 is equivalent to RV1+RV2 in the circuit. In our case, to adjust the voltage in the range from 7.25V to 10.5V, we take R4 = 1.8 kOhm, variable resistor RV1 = 4.7 kOhm and the trimming resistor RV2 is 10 kOhm with an initial approximation of 8.8 kOhm (after assembling the circuit, it is best to set its exact value by measuring the voltage at the output of LM2576 at the maximum resistance of RV1).
I decided to make a board for this regulator (the dimensions did not matter, since there is enough space in the monitor to mount even a large board):

Control board assembly:

After installation in the monitor:

All assembled:

After assembly everything seems to work:

Final option:

Advantages:

Sufficient brightness
Step-down regulator does not heat up and does not warm up the monitor
There is no PWM, which means nothing blinks at any frequency
Analogue (manual) brightness control
No restrictions on minimum brightness(for those who like to work at night)

Flaws:

The white balance is slightly shifted towards green tones (but not much)
At low brightness (very low), unevenness in the glow of LEDs of different assemblies is visible due to the spread of parameters

Improvement options:

White balance is adjustable both in the monitor settings and in the settings of almost any video card
You can try installing other LEDs that will not noticeably disrupt the white balance
To eliminate the uneven glow of LEDs at low brightness, you can use: a) PWM (adjust the brightness using PWM by always supplying the rated voltage) or b) connect all the LEDs in series and power them with an adjustable current source (if you connect all 180 LEDs in series, you will need 630V and 20mA), then the same current should pass through all the LEDs, and each one will have its own voltage drop; the brightness is regulated by changing the current and not the voltage.
If you want to make a PWM-based circuit for LM2576, you can use a NAND circuit at the On/Off input of this Step-down regulator (similar to the above circuit for LM2941), but it is better to put a dimmer in the gap of the negative wire of the LEDs via a logic-level mosfet

Quite recently - in the midst of summer, a report was published on our website Samsung LED TVs: from Kaluga with love, dedicated to the opening of the Russian Samsung plant for the production of various electronics and household appliances - Samsung Electronics Rus Kaluga (SERK). Let me remind you: key point the report was a story about the launch production lines for the production of the most modern and most relevant Samsung flat-panel TVs with LED backlighting today - the so-called LED TV. Since then, the editorial mail has received more than once letters in which our readers ask us to tell them more about LED TV technology. The main questions lie in the plane technical details technology, its advantages over competing proposals, and so on. But almost always we are talking about the price factor: is it really worth paying for an LED TV an amount that is sometimes more than twice the cost of an LCD and plasma TVs with similar diagonals and screen resolution, will there be a real return on such costs? What is typical is that as time passes, the relevance of the questions asked does not decrease. Flat panel TVs are becoming fashionable, and their range is constantly expanding. You don’t have to look far for an example: there are plans Kaluga plant Samsung Electronics will release by the end of the year about 75 thousand televisions of all three LED TV series - 6000, 7000 and 8000, with diagonals of 32, 37, 40, 46 and 55 inches and with special emphasis on the most popular 32- and 40-inch models . Already now these models are present on the shelves of most Russian retail chains, along with this, the choice of “LED” TV models from other companies is growing, so the growing interest in this technology is quite understandable. In short, today we publish brief overview features of the production technology of flat panel displays with LED backlighting.

LED TV or LED LCD TV?

To begin with, it is worth deciding on the terminology that has been established by now. The term LED TV, first introduced by Samsung Electronics and used by a number of companies, and various variations of this term like LED-backlit LCD, used by other companies, in practice means that we are talking about the good old flat-panel LCD screen, but equipped with a more modern and high-quality backlight – LED. In other words, to say that LED TV is exactly LED TV from a technical point of view it would not be entirely correct. Various technologies where light-emitting diodes form the “picture” - such as OLED, OEL or AMOLED, belong to a slightly different class of displays. Real led screen– where each pixel is displayed using one LED or a group of LEDs, can be found, for example, on huge billboards, looking at which from afar we see a whole picture, and not individual LEDs. Another example is organic LED displays. Light-Emitting Diode, OLED), where certain types of organic polymer materials emit light when exposed to electric current. OLED technology is truly promising as the basis for the production of high-quality displays for televisions and monitors - such displays are lighter, do not require backlighting, have better color rendition, a larger brightness range, lower power consumption, and in some versions even flexibility. Moreover, as technology improves, it is expected that over time the production of OLED displays will become even more profitable than the production of LCD screens. However, due to a number of technological limitations - for example, the lifespan of blue polymer phosphors, which is noticeably shorter than that of red and green organic LEDs, currently OLED technology used mainly in the production of small diagonal screens for various mobile devices. Serially produced OLED TVs Currently they have a small diagonal; rather, they are rare exotics with a huge price rather than a mass product. Although, I repeat, the prospects for the technology are promising. So, let's focus on the fact that the application term LED TV in practice means: we are talking about an LCD TV equipped with modern LED(LED) backlight. In other words, it would be appropriate to label such TVs as LED LCD TV. However, in everyday life, Samsung has nevertheless adopted a shorter and, apparently, more convenient option in marketing terms - LED TV. Or LED-backlit LCD in other versions.

LED TV vs CCFL LCD TV

Everything is learned by comparison. Until recently, we used LCD TVs and monitors, most of them equipped with traditional backlighting based on so-called cold cathode fluorescent lamps (CCFL), in other words, fluorescent lamps. The production of screens using CCFL LCD technology has been “tested” on many generations of such devices and is currently relatively inexpensive, and the convenience compared to the previous generation of displays is cathode ray tubes, mainly such as lower weight and lower energy consumption, have led to the widespread (although not complete) displacement of the latter from everyday use. And everything would be fine, but illumination using fluorescent lamps has a number of disadvantages that can be considered fundamental. For example, with CCFL backlighting it is quite difficult to realize really deep black tones - constantly switched on lamps still create a certain “leakage” of light even in those parts of the image that, according to the idea, should be dark at the moment. This also logically implies a subjectively perceived decrease in picture clarity. In addition, backlighting using fluorescent lamps makes it difficult to reproduce many shades of color, resulting in good results. color saturation turns out to be very difficult. Among other problems of CCFL LCD technology, one cannot fail to note the difficulty in achieving high frequencies sweeps, limited period service life of lamps, relatively high energy consumption, and, finally, an environmental nuance - the need to use mercury in lamps. In a word, one way or another, the need to replace fluorescent lamps with something more efficient has matured a long time ago, and as a result of numerous experiments, the choice fell on LED backlighting. It can improve at least four key factors of image quality: brightness, contrast, image clarity and color scheme. Not to mention the more uniform nature of such illumination, which is important when viewing dimly lit scenes with initially low contrast. In addition to this, it is also worth mentioning that the efficiency of LEDs and longer time operation without loss of characteristics can significantly reduce the power consumption of LED TV compared to conventional LCD TVs with CCFL LCD technology.

LED backlighting varies

To date, a number of various technologies backlighting LCD screens using LEDs. As a rule, to create backlight modules (Back Light Unit, BLU), LED arrays composed of white or multi-colored RGB (Red, Green, Blue) LEDs are used. The backlight principle is also represented by two main options: direct (Direct) and edge (Edge). In the first case, it is an array of LEDs located behind the LCD panel. Another method that allows you to create ultra-thin displays is called Edge-LED and involves placing backlight LEDs around the perimeter of the inner frame of the panel, and uniform distribution of the backlight is carried out using a special diffuser panel located behind the LCD screen - as is done in mobile devices. Proponents of direct LED backlighting promise better results due to more LEDs and local dimming technology to reduce color casting. Reverse side direct illumination - more LEDs and a concomitant increase in energy consumption and price. In addition, you will have to forget about the ultra-thin design of the TV. Proponents of edge lighting, in addition to saving energy, promise no worse quality with a thinner design. Today, many global companies are engaged in the production of LCD TVs with LED backlighting, including including Samsung Electronics, Toshiba, Philips, LG Electronics, Sony and others. Each company uses variations of the above technologies in its LCD TVs and LED-backlit monitors. For example, Sony TVs use technology Edge LED, which made it possible to significantly reduce the thickness of fairly large TVs.

However, further we will look at LED TV technology using the example of Samsung Electronics TVs - for the reason that currently in Russia Samsung’s share of the LED TV market reaches 98%.

Samsung LED backlighting: how it works

At its core, an LCD screen is a multilayer “pie” made up of color filters, liquid crystal arrays, backlight lamps, etc. The liquid crystal cells themselves do not glow, but, depending on the voltage level applied to them, they open to allow light to pass through fully, partially open, or simply closed when a dark area of the picture is displayed.

The role of the backlight lamps in this whole story is to illuminate the slightly opened LCD cells so that the final picture appears on the screen. Despite such a simplified retelling of the operating principle of the LCD display, this is quite enough to understand the purpose of its main components. The thickness of the layers of the “pie” of different LCD screens is different. When using traditional fluorescent lamps, the backlight layer is so thick that it occupies more volume than all other layers combined.

Let's replace the fluorescent lamps backlighting the LCD cells with LEDs. The first obvious effect of such a replacement is a significant reduction in the overall thickness of the LCD panel. Moreover, in Samsung LED TVs, the LEDs are placed not behind the matrix, but along its edges, due to which the presence of such an end layer has practically no effect on the overall thickness, but the overall weight is significantly reduced.

The LED BLU light-directing layer ensures uniform illumination in all areas of the screen. Thanks to a special reflective grille, the light transmission efficiency of Samsung LED TVs is stated to be 20% higher than that of models with direct RGB LED backlighting. In addition, instead of the usual 10 or more centimeters in thickness, it turns out to be less than 3 cm - if you want, put such a TV on a shelf, or if you want, hang it like a picture on the wall using a specially designed lightweight mounting system. The thickness of Samsung LED TVs 8000 series in the thinnest part of the body is 11 mm, in the thickest part - 29.9 mm. In advertising, Samsung always indicates the value obtained by measuring the thickest part of the case.

For reference: Samsung 8000 series LED TVs use 324 LEDs for backlighting. Thanks to the complete elimination of fluorescent lamps, LED TVs do not contain a single gram of mercury. IN Samsung technology in addition to this, it was also possible to completely get rid of soldering using lead compounds, and to practically reduce emissions of volatile organics and other harmful by-products by eliminating the use of sprayed powder paints - the thin, durable and attractive body of the new TVs is made using special technology Casting Crystal Design. Another significant advantage of LED TVs is high level image contrast, significantly overlapping best performance traditional LCD matrices. The brightness of LEDs is so high that, for example, in LED TVs Samsung series 6000, 7000 and 8000 the contrast ratio reaches 1,000,000:1. In addition, digital signal processing with Mega Dynamic Contrast technology provides detailed image in low-contrast “twilight” areas of the picture.

Maximum possibilities new system The backlight is squeezed out using a multi-layer Ultra Clear Panel filter, which transmits light from inside the screen and does not reflect it from the outside, so it is possible to achieve better brightness and contrast with a minimum of glare, regardless of how the screen is lit from the outside - sunlight or artificial electric lighting. LED backlight allows you to achieve white illumination of LCD cells, as a result of which it is possible to display a wider and more natural range of color shades. Color palette LED TVs produce richer and richer greens and blues of bright areas compared to conventional models no longer look faded and pale. In Samsung LED TVs, color saturation is also additionally monitored by the Wide Color Enhancer Pro hardware technology. Often, the weak point of LCD screens is the blurred image with a long response time, which reduces the sharpness of the image and reduces the smooth movement of objects in dynamic scenes. In the new Samsung LED TVs, this is monitored by the Motion Plus interpolation system: models of the 6000 and 7000 series have double the 100-Hz scan, and the flagship 8000 series have quadruple the 200 Hz scan.

An important factor is electricity consumption. Traditional LCD TVs are, of course, more economical than previous models with cathode ray picture tubes, but don’t forget that the diagonals are no longer the same, so with large LCD TVs, electricity meters still spin quite quickly. As for the new LED models, LED backlight allows you to significantly reduce energy consumption without compromising image brightness.

In addition to significant energy savings - up to 40% compared to traditional LCD models with the same diagonal, Samsung LED TVs can also boast certification to one of the most stringent environmental standards, Energy Star 3.0.

LED TV Samsung: it's not just a TV...

Everything on a TV should be perfect - both characteristics and appearance, and a set of functions. Since we are talking today about specific Samsung LED TVs produced today in Kaluga, it would be an omission not to mention their main characteristics. This is only indirectly related to the topic of today’s article; however, I believe a few lines of details about the potential item of purchase will not be superfluous.

First of all, Samsung LED TVs of the 6000, 7000 and 8000 series, along with receiving traditional analogue channels, are ready to work with digital TV thanks to the presence of built-in DVB-T/C tuners. Whenever the era of ubiquity arrives digital television in Russia, you are already ready for this. In addition, the LNA plus tuner used in these models was created specifically taking into account Russian specifics - interference, vast open spaces and not the first freshness of television repeaters. In addition to this, thanks to the presence of two ports USB new TVs can be used as a photo frame for viewing photos from a flash drive, watching multimedia videos in DivX/Xvid formats, for example, from an external USB hard drive, but it won’t be enough - there is a built-in 2 GB of flash memory with pre-loaded content. The TV can be “registered” in the home network with access to laptops, desktops and external data storage, and the TV remote control turns into wireless keyboard to navigate through folders, display content from different places networks. For Internet access there is LAN connector and support for Internet@TV with access to YouTube. The sound system in ultra-thin LED TVs is on par with the best Samsung models. A unique flat subwoofer was created especially for ultra-thin LED TVs, plus well-proven hidden speakers are used.

Finally, connection with consumer electronics DVD player, Blu-ray player, AV receiver, cinema, HD video camera, game console, can be done using an HDMI connection, of which four are provided in the design of Samsung LED models.

LED TV: are there any disadvantages?

Yes, but what about: this is the price. So far, LED TVs are much more expensive than their traditionally backlit counterparts. However, the way out of such a price situation will be traditional: lower prices as demand grows and mass production increases. So far, the size of the LED TV market is small, but the interest in such models due to their outstanding characteristics is enormous all over the world. According to Display Search analysts, next year every fifth TV sold will be made using LED TV technology, and in a couple of years – every second. By this time, we can expect prices to decline.

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 this technology works. 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 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 individual LEDs small size. In this case, each of the diodes is responsible for illuminating a certain 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 with direct backlighting is adjusted separately from other areas. Static Contrast it 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.

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.
Fine image details disappear in dark areas.
Colored halos appear where contrasting colors meet.

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. Using direct technology, you can achieve the most optimal color coverage and ensure the best quality of color reproduction. However, it is worth noting that displays with direct technology consume more electricity and are thicker.
Edge – white LEDs along with a diffusion panel are located around the perimeter of the screen. Edge TVs are more energy efficient and thinner, but good local dimming is difficult to achieve. 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 make color gamut better. However, the required color gamut was not achieved, since there was often too little of it. Therefore, based on this technology, other light diodes, allowing to achieve desired result. So, today ice TVs are used quantum dots or GB-R LED and RB-G LED diodes.

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

*Advantages*	*Flaws*
High contrast video	High cost
High clarity and realism achieved with high response speed	A small number of TV models with a small diagonal
Environmental friendliness associated with low energy consumption, as well as the absence of mercury and harmful aerosols in edge-type lighting
Stylish TV appearance
LED durability
A large number of additional functions
Availability of 3D and Smart TV functions in some models

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.

LED backlighting is another characteristic of TVs and monitors, which has recently complicated the buyer’s choice, requiring him to think twice and make a responsible decision... The fact is that LCD TVs are becoming more and more numerous, and their types are increasing time multiply.

Indeed, when purchasing a TV, you want not to make a mistake, not to buy something that represents yesterday or the day before yesterday, which you will soon no longer be able to use...

Fortunately, there are no big difficulties in this issue; its importance is greatly exaggerated - more on this below on the page...

There is a good rule: when buying a TV, it is recommended to pay less attention to the names of the technologies used, and be more guided by your impressions of its appearance and image quality.

At the same time, of course, a more modern (and expensive) TV will in most cases be of better quality.

The best results in image quality today, perhaps, are provided by the type of backlight - Direct (Full) LED. Moreover, it is being improved all the time - now this technology can use a very large number of LEDs, which, naturally, has a very positive effect.

Edge LED or its derivatives also show increasingly better characteristics, also making it possible to make TVs very thin.

In both cases, the best TV models also use the “Local Dimming” method - Local Dimming. In LG TVs, the backlight using it is called LED plus.

The LCD elements that make up LCD TV panels will not produce images on their own unless they are backlit. Therefore, one or another type of backlighting is necessarily present in modern TVs. It should be borne in mind that technologies are constantly improving, and the type of illumination with the same or similar name next year may be very different in execution from last year. For example, Full LED screens are now produced almost as thin as Edge LED.

Among the types of TV backlights used or used by SONY are the following:

CCFL (Cold Cathode Fluorescent Lamp).

WCG-CCFL (Wide Color Gamut Cold Cathode Fluorescent Lighting).

RGB LED, or dynamic rgb led (Provides color illumination of individual fragments of the monitor or TV screen. Potentially a very promising technology, since in theory it makes it possible to illuminate desired area screen in a certain color. In practice, its theoretical advantages compared to other types cannot always be realized. See details below on the page).

Full LED. Other name Direct LED(backlight diodes are located behind the screen evenly over its entire area. This simplifies control and improves quality. But it negatively affects the thickness of the screen.) - Edge LED (The liquid crystal screen is illuminated by white LEDs installed at the top and bottom or on the sides. Allows you to make very thin Slim TVs).

Dynamic Edge LED (In addition, Local Dimming technology is used, which controls the amount of illumination of individual groups of LEDs depending on the displayed image).

Intelligent Dynamic LED. Another name is Full LED or Direct LED (Compared to previous technologies, many more white illuminating LEDs are used, located directly behind the TV screen evenly across its entire area and illuminating the image. By controlling the glow of individual blocks of LEDs, the system can illuminate specific areas of the image, leaving others dark. This technology simplifies operation and improves quality, but has a negative impact on screen thickness.)

Other TV manufacturers, Samsung, Sharp, LG or Toshiba use different technologies to varying degrees. Accordingly, the TV backlight options may also have a different name (you can get a lot of information about technologies on the Internet, but from the point of view of choosing an option for purchase, this information will not give much. It is more important, as we have already said, to evaluate the TV picture visually).

By the way, Full LED (Intelligent Dynamic LED) from Sony is not the same as full LED backlighting in the original sense at the beginning of technology development, when the fluorescent lamp backlight of the LCD matrix of TVs was simply replaced by thousands of individual light-emitting diodes (LEDs).

Compared to previously used technologies, LED There are quite a lot of advantages to backlighting LCD (LCD) TVs, but there are also disadvantages (inherent to the technology itself):

Disadvantages of LED technology

Initially, this type of backlight does not improve the viewing angles of the LCD (LCD) display
- Thinner models with edge LED backlighting may suffer from uneven screen illumination
- LED backlighting can lead to local unwanted darkening of the image.

Of course, in most cases these shortcomings are successfully overcome in specific models of TVs and monitors, since the technology itself is constantly being improved. In addition, not only the backlight affects the quality of the picture on the screen.

Advantages of LED TVs

All LED types backlights are more economical
- Technologies Edge type LED allows you to create TVs with very thin screens
- LEDs does not contain mercury (although their manufacturing technology uses gallium and arsenic)

Of course, miracles do not happen. As a rule, a more expensive model will have a higher-quality image and what is considered the most promising type of screen backlight at the moment. But the image will be good not only and not necessarily because of the backlight. All other TV devices, including the video processor, can be very good quality. The TV can be very well tuned (what used to be called "calibrated"). In the end, adjustments can be made correctly and appropriately for the given lighting...

From all this, in our opinion, we can conclude:

When choosing a TV, you should not pay much attention to the type of backlight. It will be better if you personally compare the image quality of several models and choose the one whose picture seems nicer.

And choosing which type of backlight is better is the task of manufacturers. While they themselves cannot come to an established opinion (which is natural, because technology is moving forward very quickly).

Take for example RGB LED backlight It is believed to provide a much richer color gamut, extremely sharp and contrasting images on the screen, but it has not become widespread over time. On the contrary, it seems that manufacturers are abandoning it. Firstly, it is much more expensive than other types. It also has technical limitations: the number of backlight elements is limited, since controlling every part of the monitor is too difficult and expensive. As a result, some of the scene illumination that should be bright may be reduced.

Addition:

Lately There is information about successful improvements to this technology by Mitsubishi. Moreover, they are developing a completely new type of backlighting, RGB Backlit, using a three-color laser. Perhaps soon about RGB backlight they will speak in full voice again.

Sergey Filinov