LED lights

Computer technology replaces one another, if some ten years ago LCDs were a novelty, today they are the ones that dictate fashion. The new technology of LED lighting, which has entered this niche, will definitely conquer it in the next few years. And for that there are weighty reasons – starting from the notorious ecology, ending with novelty, fashion, in the end – with economic realities.

But, like any technology, this one has its own merits and demerits, in which we will understand. Usually any user who is familiar with the realities of IT will happily exchange his LCD monitor for a similar one, which has LED-backlighting, but hardly anyone will be able to clearly and accurately describe the advantages of the new technology. The answer is hampered by many myths, some of which we will consider.

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

LCD monitors are in principle worse than LED displays.

This myth emerged due to the fact that the confusion arose already at the level of fundamental concepts. The fact is that some manufacturers are trying to allocate their devices to a special class, calling them LED displays. Well, this approach is understandable from marketing positions, but illiterate in terms of technical terms. LED displays, or LED displays are called a highly specialized class of visualization devices, which has nothing to do with desktop monitors of computers. These include advertising and information displays, which are located on the streets of major cities. In such displays, a pixel is formed using one or more LEDs, and therefore the name LED-monitors was formed. These devices have high brightness, but low resolution. Those devices that we consider, which are computer LCD displays with LED backlight, have nothing to do with them. After all, in them the pixel is still formed with the help of a matrix, in cells of which the liquid crystals change the plane. By the arrival of LEDs in these devices, a light source is changed, the transmission of which is controlled by the matrix. In conventional LCD displays, cold cathode fluorescent lamps (CCFL) are used. By their arrangement they resemble tubular fluorescent tubes, only much less than them. In order for them to work stably, a high-voltage source is required, but modern bright LEDs can shine almost the same, only they do not need high current and much energy for this. As soon as the technology became mature and economically justified, it naturally acquired an industrial scale, appearing in computer displays. Returning to the myth, we can say that these LED-displays can not be perceived as worse or better than LCDs, since these are absolutely different classes of devices. Considered by us LCD monitors with different types of lighting, do not have fundamentally beneficial differences. However, about this below.

LED-backlighting is everywhere the same, like CCFL.

This statement is incorrect even with respect to the CCFL illumination, because the types of lamps used in it seriously differ from the characteristics of the produced devices. For example, the use of lamps with an improved phosphor allowed to produce displays with extended coverage of colors. In the LED backlighting, too, not everything is simple, the fact is that there are several types of it, significantly different according to the principle of action. These two approaches radically differ from each other, the key is the color of the used LEDs. The simplest technology for understanding is the simple replacement of CCF lamps with similar white LEDs in shape and size. Of course, you need a matrix calibration, careful selection of crystals for LEDs, but such monitors are practically the same as their counterparts with CCFL.The use of the same colored LEDs makes it possible in combination to obtain white light, the advantage is the ability to obtain any hue of the color of the illumination, which can significantly increase the color coverage and improve color reproduction. Such opportunities have become very popular among professionals. However, the use of colored LEDs significantly complicates and increases the cost of construction.

Rear and end lighting.

The design of the backlight unit can be any regardless of the above technologies. Usually, in most monitors with CCFL and in many LEDs (usually with white LEDs), end lighting is used. 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 uniform illumination, it generally can not be controlled dynamically at the zone level, it either turns on, or turns off entirely for the entire screen. Having seen a monitor or display with a thickness of the case less than 2 cm, it is safe to say that this type of lighting is used. When the backlight is used, not rulers, but groups of LEDs or individual modules located in a certain order behind the matrix on the entire screen. The main advantage is the possibility of zone control of the brightness of the backlight, which is especially in demand, for example, in TVs. This technology allows creating an excellent dynamic contrast, but leads to a significant thickening of the panel as a whole, especially for RGB LED. Today, different combinations of technologies are used – in notebooks this is end illumination on white LEDs, in expensive professional displays – rear RGB, and exotic subspecies are possible. In any case, one can not judge the advantages or disadvantages of a monitor with LEDs without knowing its exact characteristics and the technologies used.

LED backlight allows you to extend the color gamut and improve color reproduction.

Having become acquainted with the aforesaid, one 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 get the widest color coverage, more accurately display the shades. But this technology is quite expensive, therefore, for the mass market, a cheaper butt-end white light is used. But for white LEDs, the radiation spectrum is lower than for the RGB LED triads, so the color coverage on such monitors is already there. In this regard, you can compare with traditional CCFL. But the accuracy of color rendering depends not only on the properties of the backlight, but also on the characteristics and type of the LCD matrix – VA and IPS varieties are in any case more advantageous than TN. Therefore, they say about the color rendition and color coverage, it is still necessary to specify what type of backlighting and LCD matrix in question.

With LED backlight monitors have a higher contrast.

First, let’s clarify that in this case we are talking about dynamic contrast, since the static contrast does not depend in principle on the light source. Dynamic contrast is a very ambiguous quantity, which depends on the algorithm of the control unit and on the nature of the content being reproduced. But in the case of LED backlighting, the effect of the backlight with zone control or Local dimming is added. If there are bright and dark areas in the video frame, then the usual dynamic contrast algorithm practically does not work, the real contrast will be equal to the static value. Using local dimming allows you to selectively extinguish the highlight in darkened areas and increase in dark areas. This allows within one frame to use the difference in brightness, which ensures high contrast. It is clear that the use of such technology requires a special control unit and special logic, such opportunities are realized in LCD TVs of premium class.For monitors with conventional end illumination, manufacturers sometimes claim dynamic contrast values ​​of up to 5,000,000: 1. It is necessary to understand that the LEDs can be turned off and on almost instantaneously, without wasting time for stabilization. To measure the dynamic contrast, the brightness of the white and black colors is correlated, but if you turn off the backlight at all when black is displayed, you can get an arbitrarily large number by dividing by zero, which is successfully used by marketers. Actually, without Local dimming, when watching movies, a deep black color will be problematic. Thus, we can agree with the statement that LED backlighting gives a great dynamic contrast, only for computer users is much more important static contrast, and for her the presence or absence of LEDs is not decisive.

LED backlight guarantee high uniformity.

LCD panels are characterized by uneven lighting. There can be many reasons for this. This may be unevenness in the emission of light sources, namely, brightness differences along the length of the CCF lamp or a line of LEDs, there may be different brightness and chromaticity of the RGB triads, light guides, scatterers, polarizers may become a different source of unevenness … As you can see, highlighting is not the only possible problem . Although this is the task to solve just the same and possible. You can compensate for the brightness and color unevenness of the LCD panel by zone calibration at the factory, and enter correction factors for the matrix over the entire screen area. However, this requires expensive equipment and large time costs, because you have to calibrate every monitor. This procedure is really carried out by NEC and EIZO, but only for professional monitors of the highest price category. It would seem, why manufacturers can not provide software for calibration, so that each user himself could perform this procedure on his own? Obviously, not every display allows introduction of correction factors at the level of individual zones over the area of ​​the matrix. So the problem of the unevenness of the LCD panel is not limited to just the highlight, being a rather complex issue. Measurements of the uniformity of the backlight on a white background showed results comparable to those of CCFL, but white and especially black field shots still indicate that the problem with the unevenness of the LED backlight is not completely solved.

LED backlight, unlike CCFL does not flicker, so it’s easier for eyes to work with it.

It is worth noting 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 really shimmer, only that the flicker frequency is too high to notice it with the naked eye. But to see this is quite simple. To do this, take a pencil or any extended object and bring it to the monitor with a white fill. Holding an object at one end, you should sway it sideways at a frequency of several times per second and with such amplitude that the blurred image reminds the fan. If the monitor has a brightness below the average, which is usually comfortable for the eyes, then instead of a smooth visual trace, the pencil will leave a discrete, consisting of a sequence of relatively clear images. But with the maximum brightness of the screen the image will be the same as on the background of any source of continuous light – a lamp or a window. This stroboscopic effect, which occurs when the brightness of the backlight of the LCD screen decreases, indicates that it is extinguished and ignited at a certain frequency, high enough to see it in sight. This method of brightness control is called pulse width modulation (PWM). It is interesting that the effect on brightness of brightness changes with a frequency of up to 400 Hz has not yet been thoroughly studied, perhaps it is unsafe.But twisting the brightness to maximum in office or home lighting conditions will definitely bring a much greater harm to the eyesight. Installing the same front of the monitor with maximum brightness of the additional filter will clearly be a redundant tool for the usual use of computers. Until recently, manufacturers did not know how to deal with this phenomenon, since continuously controlling the brightness of CCFL glow is possible only within small limits. But in LEDs the range of brightness variation is much wider, in theory, changing the current consumption, you can control the brightness and without PWM. But in practice, this method is much more expensive, and it gives only a lack of flicker, which consumers do not already feel. As a result, most LED-monitors, like their CCFL ancestors, adjust the brightness all the same with the help of PWM, that is, they also flicker.

CCFL backlighting is disadvantageous compared to LED.

Immediately, this statement is true. And you can prove this by simply reviewing the characteristics of monitors. It is the LEDs from all artificial light sources that have the maximum number of lumens per 1W. Of course, the effectiveness of LEDs is not everything, because you still need to take into account the efficiency of their power supply and other, albeit not so important, factors. The conducted researches showed a curious fact, professional monitors with RGB LED power consumption is still quite high, but devices with a white backlighting are lower almost twice as compared to similar models with CCFL.

Monitors with LEDs are much more environmentally friendly than their CCFL counterparts.

Known fact – for the environment the greatest harm is brought by IT products at the stage of their production and utilization. At the first stage, quite serious environmental standards have already been introduced at the corporate level. But with recycling is not so simple, especially in our realities. It is known that fluorescent fluorescent lamps contain mercury, but often they are simply thrown into containers for household garbage. Then all this is burned, and couples enter the atmosphere. Against this backdrop, the recycling of LCD monitors does not seem a serious problem, although the CCF backlight lamps 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 struggle for ecology. Thus, the statement about the ecological compatibility of LED panels is not a myth.

LED backlighting is much more expensive than CCFL.

A few years ago this statement was undeniable. RGB LED systems still require significant development costs, and their sales are extremely low. Not surprisingly, users often choose high-quality IPS matrix with CCFL illumination with extended spectrum, because such a set is much cheaper. Regarding white LEDs, we can state that the speed of their penetration into this segment of the market testifies to the aggressive policy of vendors. After all, the market for televisions and LCD displays is almost unlimited, so considerable funds can be thrown on the fight against CCFL products. Therefore, low prices for consumer LCD displays with LED backlighting are possible and are the result of such a war. Today, the progress of LEDs is evident, there are practically no tangible advantages for CCFL. We can not fully confirm or disprove this myth, because we do not know about the true cost of LED end-lighting for manufacturers. Logic suggests that it is unlikely to significantly exceed the cost of CCFL systems. But higher retail prices for monitors with LED backlight are explained by banal marketing policy. The new technology naturally attracts consumers, creating an agiotage. While people have not yet fully learned about all the nuances – why not take advantage of this?

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