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LED lights

LED lights

Computer technologies replace one another, if some ten years ago LCD displays were new, today they are the ones that dictate fashion. The new LED lighting technology that has entered this niche will finally conquer it in the coming years. And there are good reasons for this - starting with the notorious environmental friendliness, ending with novelty, fashion, and in the end - economic realities.

But, like any technology, this one has its own advantages and disadvantages, which we will understand. Usually, any user familiar with the realities of IT will gladly exchange their LCD monitor for a similar one with LED backlighting, but it is unlikely that a person will be able to clearly and in detail describe the benefits of the new technology. The answer will be complicated by many myths, some of which we will consider.

The LED backlight technology itself is quite simple to understand, the halo of its mystery can easily be dispelled until users are finally confused by the stream of marketing slogans and research.

LCD monitors are, in principle, worse than LED displays. This myth appeared due to the fact that confusion arose already at the level of fundamental concepts. The fact is that some manufacturers are trying to separate their devices into a special class, calling them LED displays. Well, this approach is understandable from a marketing point of view, but illiterate in terms of technical terms. LED displays, or LED displays, refer to a highly specialized class of visualization devices that have nothing to do with desktop computer monitors at all. These include advertising and information displays, which are located on the streets of large cities. In such displays, a pixel is formed using one or more LEDs, which is why the name LED monitors was formed. These devices have high brightness but low resolution. Those devices that we are considering, which are computer LCD displays with LED backlight, have nothing to do with them. Indeed, in them, the pixel is still formed with the help of a matrix, in the cells of which the liquid crystals change the plane. With the arrival of LEDs in these devices, the light source has changed, the transmission of which is controlled by the matrix. Conventional LCD displays use cold cathode fluorescent lamps (CCFLs). In their structure, they resemble tubular fluorescent lamps, only much smaller. For them to work steadily, a high voltage source is required, but modern bright LEDs can glow in almost the same way, only they do not require high current and a lot of energy for this. Once the technology became mature and economically viable, it naturally took on an industrial scale, appearing in computer displays as well. Returning to the myth, we can say that real LED displays cannot be perceived as worse or better than LCDs, since these are completely different classes of devices. The LCD monitors we are considering with different types of backlighting have no fundamentally advantageous differences. However, more on that below.

LED backlighting is the same everywhere, just like CCFL. This statement is incorrect even in relation to CCFL backlighting, since the types of lamps used in it seriously differ the characteristics of the devices produced. For example, the use of lamps with an improved phosphor made it possible to produce displays with extended color gamut. In LED backlighting, not everything is simple either, the fact is that there are several types of it, which differ significantly in their principle of operation. These two approaches are radically different from each other, the key is the color of the LEDs used. The simplest technology to understand is to simply replace CCF lamps with white LEDs of the same shape and size. Of course, matrix calibration is required, careful selection of crystals for LEDs, but such monitors practically do not differ from their counterparts with CCFL. The use of colored LEDs makes it possible to obtain white light in combination, the advantage is the ability to obtain any shade of the backlight color, which significantly increases the color gamut and improves color rendering. Such opportunities have become very popular among professionals. However, the use of colored LEDs significantly complicates and increases the cost of the design.

Back and end lighting. The design of the backlight unit can be any, regardless of the above technologies. Typically, most CCFL monitors and many LED monitors (usually white LEDs) use an edge backlight. Light sources are located at the ends of the panel, under the matrix or above it. This approach allows you to create panels of small thickness, and the difficulty is to achieve uniformity of backlighting, it cannot be dynamically controlled at all at the zone level, it either turns on or off completely for the entire screen. Seeing a monitor or display with a case thickness of less than 2 cm, we can say with confidence that this type of backlight is used. Backlighting does not use rulers, but groups of LEDs or individual modules located in a certain order behind the matrix across the entire screen. The main advantage is the ability to zone control the brightness of the backlight, which is especially in demand, for example, in TVs. This technology produces excellent dynamic contrast, but results in significant panel thickening, especially for RGB LEDs. Today, various combinations of technologies are used - in laptops it is end-lighting on white LEDs, in expensive professional displays - rear RGB, exotic subspecies are also possible. In any case, one cannot judge the advantages or disadvantages of a monitor with LEDs without knowing its exact characteristics and the technologies used.

LED backlighting allows you to expand the color gamut and improve color reproduction. After reviewing the above, you can already guess what is the reason for the myth. Initially, LED backlighting appeared in professional displays, where its RGB technology was in demand. With the help of multi-colored LEDs, it became possible to obtain the widest color gamut, to display shades more accurately. But this technology is quite expensive, so a cheaper end-face white backlight is used for the mass market. But white LEDs have a lower emission spectrum than RGB LED triads, so the color coverage on such monitors is narrower. In this regard, a comparison can be made with traditional CCFL. But the color accuracy depends not only on the properties of the backlight, but also on the characteristics and type of LCD matrix - * VA and IPS varieties are in any case more advantageous compared to TN. Therefore, they talk about color rendition and color gamut, nevertheless it is necessary to clarify what type of backlight and LCD matrix we are talking about.

With LED backlighting, monitors have higher contrast. First, let's clarify that in this case we are talking about dynamic contrast, since static contrast does not depend in principle on the light source. Dynamic contrast is a highly ambiguous value that depends on the control unit's algorithm and on the nature of the content being played. But in the case of LED backlighting, the influence of backlighting with zone control or Local dimming is also added. If there are both light and dark areas in a video frame, then the usual dynamic contrast algorithm practically does not work, the real contrast will be equal to the static indicator. Using local dimming allows you to selectively dim the backlight in dark areas and boost in dark areas. This will allow using the brightness difference within one frame, which provides high contrast. It is clear that the use of such technology requires a special control unit and special logic, such possibilities are implemented in premium LCD TVs. For monitors with conventional backlighting, manufacturers sometimes claim dynamic contrast ratios of up to 5,000,000: 1. It should be understood that LEDs can be turned off and on almost instantly, without wasting time on stabilization. To measure dynamic contrast, the brightness of white and black is correlated, but if the backlight is turned off altogether when displaying black, then dividing by zero can get an arbitrarily large figure, which is successfully used by marketers. In reality, without Local dimming, it will be problematic to see deep black color when watching movies. Thus, we can agree with the statement that LED backlighting provides a high dynamic contrast, but for computer users, static contrast is much more important, and for it the presence or absence of LEDs is not decisive.

LED backlighting guarantees high uniformity. Uneven lighting is inherent in LCD panels. There can be many reasons for this. These can be irregularities in the emission of light sources, namely, brightness differences along the length of the CCF lamp or a line of LEDs, there can be different brightness and chromaticity of RGB triads, light guides, diffusers, polarizers can become another source of irregularity ... As you can see, backlighting is not the only possible problem ... Although it is possible to solve this problem. You can compensate for the luminance and color unevenness of the LCD panel with a zone calibration at the factory, and enter matrix correction factors across the entire screen. However, this requires expensive equipment and a lot of time, because each monitor will have to be calibrated. This procedure is really carried out by NEC and EIZO, but only for professional monitors of the highest price category. It would seem, why can't manufacturers provide software for calibration, so that each user can perform this procedure on his own? Obviously, not every display allows the introduction of correction factors at the level of individual zones across the matrix area. So the problem of unevenness of the LCD panel is not limited to just the backlight, which is a rather complex issue. Measurements of the uniformity of the backlight on a white background showed results comparable to CCFL, but the pictures of the white and especially the black field still indicate that the problem with the unevenness of the LED backlight has not been completely solved.

LED backlight, unlike CCFL, does not flicker, so it is easier for the eyes to work with it. It should be noted that many users do not even suspect that their LCD monitors flicker, believing that this phenomenon is inherent only in CRT monitors. In fact, most LCDs do flicker, except that the flicker rate is too high to be noticed with the naked eye. But it is quite easy to verify this. To do this, take a pencil or any elongated object and bring it to the monitor with a white fill. Holding the object by one of the ends, you should shake it from side to side at a frequency of several times per second and with such an amplitude that the blurred image resembles a fan. If the monitor has a brightness below average, which is usually comfortable for the eyes, then instead of a smooth visual trace, the pencil will leave a discrete one, consisting of a series of relatively clear images. But with the maximum brightness of the screen, the image will be the same as against the background of any source of continuous light - a lamp or a window. This stroboscopic effect, which occurs when the brightness of the LCD backlight decreases, indicates that it goes out and lights up at a certain frequency, high enough for you to see it with your eyes. This way of dimming is called pulse width modulation (PWM). Interestingly, the effect on vision of changes in brightness with a frequency of up to 400 Hz has not yet been properly studied, it may be unsafe. But turning the brightness to maximum in office or home lighting conditions will definitely do much more harm to vision. Installing an additional filter in front of the monitor with maximum brightness would be clearly redundant for normal computer use. Until recently, manufacturers did not know how to deal with this phenomenon, since it is possible to continuously control the brightness of the CCFL luminescence only within small limits. But for LEDs, the range of brightness changes is much wider, in theory, by changing the current consumption, you can control the brightness without PWM. But in practice, this method is much more expensive, and it gives only the absence of flicker, which consumers do not feel anyway. As a result, most LED monitors, like their CCFL ancestors, still adjust brightness using PWM, that is, they flicker in the same way.

CCFL backlighting is disadvantageous compared to LED. Let's say right away that this statement is true. And this can be proved by a simple overview of the characteristics of monitors. It is the LEDs from all artificial light sources that have the maximum number of lumens per watt. Of course, the efficiency of LEDs is not all, because you still need to take into account the efficiency of their power supply and other, albeit not so important, factors. The conducted studies have shown an interesting fact, that the power consumption of professional monitors with RGB LED is still quite high, but devices with edge white backlighting are almost two times lower than that of similar models with CCFL.

LED monitors are much more environmentally friendly than their CCFL counterparts. It is a well-known fact that the greatest harm to the environment is brought by IT products at the stage of their production and disposal. At the first stage, quite serious environmental standards have already been introduced at the corporate level. But disposal is not so simple, especially in our realities. Fluorescent fluorescent lamps are known to contain mercury, but they are often simply thrown into household waste containers. Then all this is burned, and the vapors enter the atmosphere. Against this background, the disposal of LCD monitors does not seem to be a serious problem, although CCF backlights also contain mercury. But the use of LEDs, in principle, reduces these risks. So the use of LED monitors, firstly, is an energy saving factor, and secondly, it is also a step in the fight for the environment. Thus, the statement about the environmental friendliness of LED panels is not a myth.

LED backlighting is noticeably more expensive than CCFL. A few years ago, this statement was indisputable. RGB LED systems still require significant development costs and sales are extremely small. It is not surprising that users often choose high-quality spread spectrum CCFL backlit IPS matrices, since such a set is much cheaper. As for white LEDs, we can state that the speed of their penetration into this market segment testifies to the aggressive policy of vendors. After all, the market for TVs and LCDs is almost limitless, so significant funds can be thrown into the fight against CCFL products. Therefore, low prices for consumer LCDs with LED backlighting are possibly a consequence of such a war. Today the progress of LED is obvious, CCFL has practically no significant trump cards.It is impossible to fully confirm or refute this myth, because we do not know about the true cost of LED end-lighting for manufacturers. Logic suggests that it is unlikely that it will significantly exceed the cost of CCFL systems. But the higher retail prices for LED-backlit monitors are explained by banal marketing policies. The new technology naturally attracts consumers, creating a buzz. While people have not yet fully learned about all the nuances - why not take advantage of this?


Watch the video: How to Cut and Connect LED Light Strips. (June 2021).