The main differences between LCD and CRT monitors. Which is better - LCD or CRT monitor
Boris Lvovich Rosing has been working with Brown's pipe since 1902. On July 25, 1907, he applied for an invention "Method electric transmission images at a distance ". The beam was swept in the tube by magnetic fields, and the signal was modulated (change in brightness) with a capacitor, which could deflect the beam vertically, thereby changing the number of electrons passing to the screen through the diaphragm. On May 9, 1911, at a meeting of the Russian Technical Society, Rosing demonstrated the transmission of television images of simple geometric shapes and receiving them with playback on the CRT screen.
At the beginning and middle of the 20th century, Vladimir Zvorykin, Allen Dumont and others played a significant role in the development of CRT.
Device and principle of operation
General principles
Black and white picture tube device
In a balloon 9 a deep vacuum is created - first, air is pumped out, then all metal parts of the kinescope are heated by an inductor to release the absorbed gases, a getter is used to gradually absorb the remaining air.
To create an electron beam 2 , a device called an electron gun is used. Cathode 8 heated by filament 5 , emits electrons. To increase the emission of electrons, the cathode is covered with a substance having a low work function ( largest manufacturers CRTs use their own patented technologies for this). By changing the voltage at the control electrode ( modulator) 12 you can change the intensity of the electron beam and, accordingly, the brightness of the image (there are also models with cathode control). In addition to the control electrode, the gun of modern CRTs contains a focusing electrode (until 1961, electromagnetic focusing was used in domestic CRTs using a focusing coil 3 with core 11 ), designed to focus the spot on the CRT screen to a point, the accelerating electrode for additional acceleration of electrons within the gun and the anode. After leaving the gun, the electrons are accelerated by the anode 14 , which is a metallized coating of the inner surface of the kinescope cone, connected to the gun electrode of the same name. In color picture tubes with an internal electrostatic screen, it is connected to the anode. In a number of early-model CRTs, such as 43LK3B, the cone was made of metal and represented the anode itself. The anode voltage ranges from 7 to 30 kilovolts. In a number of small-sized oscillographic CRTs, the anode is only one of the electrodes of the electron gun and is supplied with voltages up to several hundred volts.
Then the beam passes through the deflecting system 1 , which can change the direction of the beam (the figure shows the magnetic deflection system). In television CRTs, a magnetic deflection system is used to provide large deflection angles. Oscilloscope CRTs use an electrostatic deflection system for faster response times.
An electron beam hits the screen 10 phosphor coated 4 ... From the bombardment of electrons, the phosphor glows and a rapidly moving spot of variable brightness creates an image on the screen.
The phosphor from electrons acquires a negative charge, and secondary emission begins - the phosphor itself begins to emit electrons. As a result, the entire tube acquires a negative charge. In order to avoid this, over the entire surface of the tube there is a layer of aquadag, a conductive mixture based on graphite ( 6 ).
The kinescope is connected through the leads 13 and high voltage socket 7 .
In black and white televisions, the composition of the phosphor is selected so that it glows in a neutral gray color. In video terminals, radars, etc., the phosphor is often made yellow or green for less eye fatigue.
Beam angle
The angle of deflection of the CRT beam is the maximum angle between the two possible positions of the electron beam inside the bulb, at which the luminous spot is still visible on the screen. The ratio of the diagonal (diameter) of the screen to the length of the CRT depends on the value of the angle. In oscillographic CRTs, it is usually up to 40 degrees, which is associated with the need to increase the sensitivity of the beam to the effect of deflecting plates. The first Soviet television kinescopes with a round screen had a deflection angle of 50 degrees, for black-and-white kinescopes of later releases it was 70 degrees, starting from the 60s it increased to 110 degrees (one of the first such kinescopes-43LK9B). Domestic color CRTs have 90 degrees.
With an increase in the angle of deflection of the beam, the dimensions and mass of the kinescope decrease, however, the power consumed by the scanning nodes increases. Currently, in some areas, the use of 70-degree kinescopes has been revived: in color VGA monitors most of the diagonals. Also, an angle of 70 degrees continues to be used in small-sized black-and-white kinescopes (for example, 16LK1B), where the length does not play such a significant role.
Ion trap
Since it is impossible to create an ideal vacuum inside the CRT, some of the air molecules remain inside. When they collide with electrons, ions are formed from them, which, having a mass many times greater than the mass of electrons, practically do not deflect, gradually burning out the phosphor in the center of the screen and forming the so-called ion spot. To combat this until the mid-60s. used an ion trap, which has a major drawback: its correct installation- a rather painstaking operation, and when incorrect installation no picture. At the beginning of the 60s. a new way of protecting the phosphor was developed: aluminizing the screen, which also made it possible to double the maximum brightness of the kinescope, and the need for an ion trap disappeared.
Delay in applying voltage to the anode or modulator
In a TV, the horizontal scan of which is made on lamps, the voltage at the anode of the kinescope appears only after the output lamp of the horizontal scan and the damper diode are warmed up. The glow of the kinescope manages to warm up by this moment.
The introduction of fully semiconductor circuitry into the horizontal scanning units gave rise to the problem of accelerated wear of the kinescope cathodes due to the voltage applied to the anode of the kinescope simultaneously with switching on. To combat this phenomenon, amateur nodes have been developed that provide a delay in the supply of voltage to the anode or the kinescope modulator. Interestingly, some of them, despite the fact that they are intended for installation in all-semiconductor televisions, use a radio tube as a delay element. Later TVs began to be produced industrial production, in which such a delay is provided initially.
Scan
To create an image on the screen, the electron beam must constantly pass over the screen at a high frequency - at least 25 times per second. This process is called sweep... There are several ways to unfold an image.
Raster scan
The electron beam travels the entire screen line by line. There are two options:
- 1-2-3-4-5- ... (progressive scan);
- 1-3-5-7-…, then 2-4-6-8-… (interlaced scan).
Vector sweep
The electron beam travels along the lines of the image.
Colored picture tubes
The device is a color picture tube. 1 -Electronic cannons. 2 - Electron beams. 3 - Focusing coil. 4 - Deflecting coils. 5 - Anode. 6 - Mask, due to which the red beam hits the red phosphor, etc. 7 - Red, green and blue grains of the phosphor. 8 - Mask and grains of phosphor (enlarged).
The color picture tube differs from the black-and-white one in that it has three guns - "red", "green" and "blue" ( 1 ). Accordingly, on the screen 7 three types of phosphor are applied in some order - red, green and blue ( 8 ).
Only the beam from the red gun hits the red phosphor, the green one - only from the green one, etc. This is achieved by the fact that a metal grating is installed between the guns and the screen. mask (6 ). In modern picture tubes, the mask is made of Invar, a steel grade with a small coefficient of thermal expansion.
Types of masks
There are two types of masks:
- the actual shadow mask, which exists of two types:
- A shadow mask for CRTs with a delta-shaped arrangement of electron guns. Often, especially in translated literature, it is referred to as the shadow grid. Currently used in most monitor CRTs. TV picture tubes with mask of this type now not produced, however, such kinescopes can be found in televisions of past years (59LK3Ts, 61LK3Ts, 61LK4Ts);
- A shadow mask for CRTs with a planar arrangement of electron guns. Also known as slotted grating. Currently, it is used in the vast majority of television picture tubes (25LK2Ts, 32LK1Ts, 32LK2Ts, 51LK2Ts, 61LK5Ts, foreign models). It is almost never found in monitor CRTs, with the exception of Flatron models;
- aperture grille (Mitsubishi Diamondtron). This mask, unlike other types, consists of a large number of wires stretched vertically. The fundamental difference between a mask of this type is that it does not restrict the electron beam, but focuses it. The transparency of the aperture grille is approximately 85% versus 20% for the shadow mask. CRTs with such a mask are used in monitors and televisions. Attempts were made to create such kinescopes in the 70s and in the USSR (for example, 47LK3Ts).
- special type of color kinescopes stand apart - single-beam chromoscopes, in particular, 25LK1Ts. By design and principle of operation, they are strikingly different from other types of color picture tubes. Despite the obvious advantages, including reduced power consumption, comparable to that of a black-and-white CRT with a diagonal of the same size, such CRTs are not widely used.
There is no clear leader among these masks: the shadow one provides high quality lines, the aperture gives more saturated colors and high efficiency. Slotted combines the advantages of shadow and aperture, but is prone to moire.
Types of lattices, methods of measuring the step on them
The smaller the phosphor elements, the higher image quality the tube can give. An indicator of image quality is mask step.
- For a shadow lattice, the mask pitch is the distance between the two nearest mask holes (respectively, the distance between the two nearest phosphor elements of the same color).
- For aperture and slit gratings, the mask pitch is determined as the horizontal distance between the mask slits (respectively, the horizontal distance between the vertical stripes of the phosphor of the same color).
In modern monitor CRTs, the pitch of the mask is at the level of 0.25 mm. Television CRTs, which are viewed from a greater distance, use steps of the order of 0.8 mm.
Convergence of rays
Since the radius of curvature of the screen is much greater than the distance from it to the electron-optical system up to infinity in flat kinescopes, and without the use of special measures, the intersection point of the beams of the color kinescope is at a constant distance from the electron guns, it is necessary to ensure that this point is exactly on surface of the shadow mask, otherwise the misalignment of the three color components of the image is formed, increasing from the center of the screen to the edges. To prevent this from happening, you need to properly displace the electron beams. In kinescopes with a delta-shaped arrangement of guns, this is done by a special electromagnetic system, controlled separately by a device, which in old TVs was placed in a separate unit - a mixing unit - for periodic adjustments. In kinescopes with a planar arrangement of guns, adjustment is made using special magnets located on the neck of the kinescope. Over time, especially in CRTs with a delta-shaped arrangement of electron guns, the convergence is disturbed and needs additional adjustment. Most computer repair companies offer a service to re-align the monitor beams.
Demagnetization
Necessary in color CRTs to remove residual or accidental magnetization of the shadow mask and electrostatic screen that affects image quality. Demagnetization occurs due to the appearance in the so-called demagnetization loop - a ring-shaped flexible coil of large diameter located on the surface of the picture tube - a pulse of a rapidly alternating decaying magnetic field. In order for this current to gradually decrease after turning on the TV, thermistors are used. Many monitors, in addition to thermistors, contain a relay that, at the end of the kinescope demagnetization process, turns off the power to this circuit to cool the thermistor. After that, you can use a special key, or, more often, a special command in the monitor menu, to trigger this relay and re-demagnetize at any time without turning off and on the monitor power.
Trinescope
A trinescope is a design consisting of three black-and-white CRTs, light filters and translucent mirrors (or dichroic mirrors that combine the functions of translucent mirrors and filters) used to obtain a color image.
Application
CRTs are used in raster imaging systems: various types of televisions, monitors, video systems. Oscillographic CRTs are most often used in systems for displaying functional dependencies: oscilloscopes, wobuloscopes, also as a display device at radar stations, in special-purpose devices; in the Soviet years they were also used as visual aids in the study of the device of electron beam devices in general. Sign-printing CRTs are used in various special-purpose equipment.
Designation and marking
The designation of domestic CRTs consists of four elements:
- First element: a number indicating the diagonal of a rectangular or circular screen in centimeters;
- The second element: the purpose of the CRT, in particular, the LC is a television kinescope, the LM is a monitor kinescope, the LO is an oscillographic tube;
- Third element: a number indicating the model number of a given tube with a given diagonal;
- The fourth element: a letter indicating the color of the screen glow, in particular, C - color, B - white glow, I - green glow.
In special cases, a fifth element can be added to the designation, carrying additional information.
Example: 50LK2B - black-and-white kinescope with a screen diagonal of 50 cm, the second model, 3LO1I - an oscilloscope tube with a green glow screen diameter of 3 cm, the first model.
Health impact
Electromagnetic radiation
This radiation is created not by the kinescope itself, but by the deflecting system. Tubes with electrostatic deviation, in particular oscilloscopes, do not emit it.
In monitor CRTs, the deflection system is often covered with ferrite cups to suppress this radiation. Television CRTs do not require such screening, since the viewer usually sits at a much greater distance from the TV set than from the monitor.
Ionizing radiation
In CRTs there is ionizing radiation of two types.
The first of them is the electron beam itself, which is, in fact, a flux of beta particles of low energy (25 keV). This radiation does not go outside, and does not pose a danger to the user.
The second is bremsstrahlung X-ray radiation, which occurs when the screen is bombarded with electrons. To reduce the output of this radiation to the outside to completely safe values, the glass is doped with lead (see below). However, in the event of a malfunction of the TV or monitor, leading to a significant increase in the anode voltage, the level of this radiation can increase to noticeable values. To prevent such situations, line scan units are equipped with protection nodes.
In domestic and foreign color televisions, produced before the mid-1970s, additional sources of X-ray radiation can be found - stabilizing triodes, connected in parallel with the kinescope, and serving to stabilize the anode voltage, and hence the size of the image. In the TVs "Raduga-5" and "Rubin-401-1" triodes 6S20S are used, in the early models of ULPCT - GP-5. Since the glass of the cylinder of such a triode is much thinner than that of a kinescope, and is not doped with lead, it is a much more intense source of X-ray radiation than the kinescope itself, therefore it is placed in a special steel screen. In later models of ULPCT TVs, other methods of stabilizing high voltage are used, and this source of X-ray radiation is excluded.
Shimmer
Mitsubishi Diamond Pro 750SB monitor (1024x768, 100Hz) captured at 1/1000 sec. The brightness is artificially high; shows the actual brightness of the image at different points on the screen.
The beam of the CRT monitor, forming an image on the screen, makes the phosphor particles glow. Until the next frame is formed, these particles have time to go out, so you can observe the "flickering of the screen". The higher the frame rate, the less noticeable the flickering. Low frequency leads to eye fatigue and is harmful to health.
Most televisions based on a cathode-ray tube change 25 frames every second, which, taking into account interlaced scanning, is 50 fields (half frames) per second (Hz). In modern TV models, this frequency is artificially raised to 100 hertz. When working behind the monitor screen, the flicker is felt more strongly, since the distance from the eyes to the CRT is much shorter than when watching TV. The minimum recommended refresh rate for the monitor screen is 85 hertz. Earlier monitor models do not allow a sweep rate of more than 70-75 Hz. CRT flickering can clearly be seen with peripheral vision.
Fuzzy image
The image on a cathode ray tube is blurry compared to other types of screens. Blurred images are thought to be one of the factors contributing to eye fatigue in the user.
Currently (2008) in tasks that are not demanding on color reproduction, from the point of view of ergonomics, LCD monitors connected via a digital DVI connector are certainly preferable.
High voltage
The CRT uses high voltage. Residual voltage of hundreds of volts, if no action is taken, can linger on CRTs and strapping circuits for weeks. Therefore, discharge resistors are added to the circuits, which make the TV completely safe within a few minutes after turning off.
Contrary to popular belief, the voltage of the CRT anode cannot kill a person due to the low power of the voltage converter - there will only be a tangible blow. However, it can also be fatal if a person has heart defects. It can also cause injuries, including fatal ones, indirectly when, by withdrawing the hand, a person touches other circuits of the television and monitor containing extremely life-threatening voltages - and such circuits are present in all models of televisions and monitors using CRTs.
Toxic substances
Any electronics (including CRT) contains substances that are harmful to health and the environment. Among them: lead glass, barium compounds in cathodes, phosphors.
Since the second half of the 60s, the dangerous part of the kinescope is covered with a special metal explosion-proof band, made in the form of an all-metal stamped structure or wound in several layers of tape. Such a bandage excludes the possibility of a spontaneous explosion. Some CRT models additionally used protective film covering the screen.
Despite the use of protective systems, it is not excluded that people will be damaged by shrapnel if the kinescope is deliberately broken. In this regard, when destroying the latter, for safety, the shtengel is preliminarily broken - a technological glass tube at the end of the neck under a plastic base, through which air is pumped out during production.
Small-sized CRTs and picture tubes with a screen diameter or diagonal of up to 15 cm are not dangerous and are not equipped with explosion-proof devices.
LCD monitors have appeared in almost every computer store, and at an affordable price. Prices have decreased by about half compared to a year ago. And they continue their precipitous decline. At the end of 2000, the price for an LCD monitor was about $ 1100, but now a mediocre display can be purchased for $ 550. Entry-level models sell for even less, sometimes under $ 300. Some models have already surpassed the $ 250 low, although you will have to look for them. The price reduction is great, but even more encouraging, LCDs have made significant advances in technology over the past year. And although LCD monitors still cannot catch up with their CRT counterparts in picture quality, this gap is constantly narrowing.
The first and most important improvement is that the viewing angle in LCD monitors has increased. The viewing angle was the weakest point of LCD monitors. V best models the vertical viewing angle has reached a value between 90 and 160 degrees. But there are quite a few pitfalls here, so that different models differ greatly in terms of viewing angle. More importantly, the number of colors has also improved. In 2000, you could find models that were only capable of displaying 16-bit color. Nowadays, almost any LCD monitor supports 24-bit color. Although from a practical point of view, this 24-bit color is still very far from CRT monitors.
Among the improvements, it will not be superfluous to note the response time of transistors, which has grown significantly over the year. As some manufacturers have announced, the response time of the new monitors is twice as fast as the previous generation. As a result, another huge disadvantage of LCD monitors, afterglow, has practically disappeared. So now on the LCD monitor, you can quite comfortably work with graphic applications and even play. By the way, we almost forgot to mention the brightness and contrast - they are also constantly improving and approaching the results of CRT monitors.
Despite roughly equal prices and flawless technology, an LCD monitor has its drawbacks compared to a CRT. Some users will never buy an LCD monitor at all for many reasons. Let's try to highlight the pros and cons of LCD and CRT monitors.
Liquid crystals or a cathode ray tube?
The first advantage of an LCD monitor is that you forget about geometry problems. These monitors are free of distortion, keystone defects, and brightness issues. The picture is geometrically flawless. Designers, fans accurate graphics, crazy about these monitors. Unfortunately, the LCD monitor has some very serious flaws that will make any artist stick to the good old picture tube.
Disadvantage 1
The best CRT monitors have a contrast ratio of 700: 1. The best LCD monitors only boast 450: 1. In addition, models with a contrast ratio of 250: 1 or even 200: 1 are not uncommon. A low contrast ratio results in dark shades being displayed as completely black. In this case, the color gradations of the picture are easily lost.
Disadvantage 2
Almost all manufacturers report support for 16 million colors. However, the matrix in most of them is capable of displaying 260,000 colors, and the Neovo F-15 succeeds in this. The result is a 16-bit color display, although the monitor is advertised as supporting 24-bit. However, it should be given credit - LCD displays have evolved significantly in recent years, although they still have not come close to the color spectrum of CRTs. Instead of displaying all the colors smoothly blending into one another, the image has a grainy, variegated texture. You will get the same effect if you reduce the number of colors in Windows.
Disadvantage 3
If you buy a new CRT display, you won't even try to use refresh rates below 85Hz. But if refresh rate is a good quality criterion for a CRT display, the same cannot be transferred directly to an LCD. In a cathode-ray tube, an electron beam scans the image on the screen. The faster the scan, the more better display, and so, accordingly, the higher the refresh rate. Ideally, your CRT display should run between 85 and 100 Hz. In the LCD, the image is created not by an electron beam, but by pixels consisting of red, green and blue subpixels (triad). Image quality depends on how quickly pixels are turned on and off. Pixel off speed is often referred to as reaction time. For the monitors we tested, it ranged from 25 to 50 ms. In other words, the maximum number of images displayed per second ranges from 20 to 40, depending on the model.
LCD vs CRT: A Brief Comparison
We have tried to summarize the main differences between LCD and CRT monitors in a table. | LCD (TFT) | CRT (CRT) | |
| Brightness | (+) from 170 to 300 cd / m2 | (~) 80 to 120 cd / m2 |
| Contrast | (-) 150: 1 to 450: 1 | (+) 350: 1 to 700: 1 |
| Viewing angle | (~) 90 ° to 170 ° | (+) more than 150 ° |
| Information defects | (+) no | (~) 0.0079 to 0.0118 "(0.20 to 0.30 mm) |
| Focusing | (+) very good | (~) acceptable to very good |
| Geometry | (+) flawless | (~) errors are possible |
| Dead pixels | (-) up to 8 | (+) no |
| Input signal | (+) analog or digital | (~) analog only |
| Possible Resolutions | (-) rigidly fixed resolution or interpolation | (+) set |
| Gamma (representation of colors for the human eye) | (~) satisfactory | (+) photographic quality |
| Monotony | (~) often lighter around the edges | (~) often lighter in the center |
| Color purity, color quality | (-) bad to average | (+) very good |
| Shimmer | (+) no | (~) invisible at more than 85 Hz refresh rate |
| Exposure to magnetic fields | (+) not affected | (-) depends on shielding, may be highly susceptible |
| Pixel response time | (-) 20 to 50 ms | (+) not noticeable |
| Energy consumption | (+) 25 to 40 W | (-) 60 to 160 W |
| Dimensions / weight | (+) minimal | (-) large dimensions, heavy weight |
(+) - advantage, (~) - average, (-) - disadvantage
Basic principles of LCD monitor operation
LCD monitors implement three different liquid crystal technologies - TN + film, IPS and MVA. But regardless of the technology used, all LCD monitors are based on the same fundamental operating principles.
One or more neon lights provide a backlight to illuminate the display. The number of lamps is small in cheap models, while in expensive ones up to four are used. In fact, using two (or more) neon lights does not improve image quality. It's just that the second lamp serves to ensure the monitor failsafe if the first one breaks. This extends the life of the monitor, as the neon lamp can only last 50,000 hours, while the electronics can last between 100,000 and 150,000 hours.
To ensure the uniformity of the monitor's glow, the light passes through the reflector system before hitting the panel. The LCD panel is actually an extremely complex device, although it is not noticeable at first glance. The panel is a complex device with many layers. We note two layers of polarizers, electrodes, crystals, color filters, film transistors, etc. There are 1024 x 768 x 3 = 2,359,296 subpixels in a 15 "" monitor. Each subpixel is controlled by a transistor that outputs its own voltage. This voltage can be very variable and causes the liquid crystals in each subpixel to rotate through a certain angle. The angle of rotation determines the amount of light that passes through the subpixel. In turn, the transmitted light forms an image on the panel. The crystal actually rotates the axis of polarization of the light wave, since the wave passes through the polarizer before entering the display. If the axis of polarization of the wave and the axis of the polarizer coincide, the light passes through the polarizer. If they are perpendicular, no light will pass through. More detailed information the essence of the polarization effect can be gleaned from the physics textbook for the 11th grade.
Liquid Crystals - Medium State
Liquid crystals are a substance that has the properties of both a liquid and a solid. One of the most important properties of liquid crystals (this is what is used in LCD displays) is the ability to change its orientation in space depending on the applied voltage.
Let's delve a little deeper into the history of liquid crystals, as it is quite interesting. As usual in science, liquid crystals were discovered by accident. In 1888, Friedrich Reinitzer, an Austrian botanist, studied the role of cholesterol in plants. One of the experiments involved heating the material. The scientist found that the crystals become cloudy and flow at 145.5 °, and then the crystals turn into liquid at 178.5 °. Friedrich shared his discovery with Otto Lehmann, a German physicist who discovered the properties of a crystal in a liquid in relation to its reaction to light. Since then, the name "liquid crystals" has gone.
The illustration shows a molecule with crystal properties - methoxybenzilidene butylanaline.
Enlarged image of liquid crystal
TN + Film (rolled crystal + film)
Figure 1: In TN + film panels, liquid crystals line up perpendicular to the substrate. The word "film" in the name comes from an additional layer that serves to increase the viewing angle.
TN + film is the simplest technology, since it is based on all the same twisted crystals. Twisted crystals go back years - they are used in most TFT panels sold over the past few years. To improve the legibility of the image, a film layer has been added to increase the viewing angle from 90 ° to 150 °. Unfortunately, film does not affect contrast levels or reaction times, which remain poor.
So, at least in theory, TN + film displays are the cheapest, budget solutions... Their manufacturing process is not much different from the manufacture of previous panels on twisted crystals. Today there are no cheaper solutions than TN + film.
Let us briefly dwell on the principle of operation: if the transistor applies zero voltage to the subpixels, then the liquid crystals (and, accordingly, the axis of polarized light passing through them) rotate 90 ° (from the back to the front). Since the axis of the polarizer filter on the second panel differs from the first by 90 °, light will pass through it. When the red, green and blue subpixels are fully utilized, together they create a white dot on the screen.
If we apply voltage, in our case the field between two electrodes, then it will destroy the spiral structure of the crystal. The molecules will line up in the direction of the electric field. In our example, they will become perpendicular to the substrate. In this position, light cannot pass through the subpixels. The white point turns to black.
The twisted crystal display has several disadvantages.
First, engineers are already very long time struggling to get the liquid crystals to line up strictly perpendicular to the substrate when the voltage is turned on. It is for this reason that older LCDs could not display crisp blacks.
Second, if the transistor burns out, it can no longer apply voltage to its three subpixels. This is important because zero voltage means a bright dot on the screen. For this reason, LCD dead pixels are very bright and visible.
As for the 15 "" monitors, only one technology has been developed for them to replace TN + film - MVA (more on that later). This technology is more expensive than TN + film, but it surpasses TN + film in almost all respects. However, we mention "almost" because in some cases TN + film performs better than MVA.
IPS (In-Pane Switching or Super-TFT)
Figure 2: If voltage is applied, the molecules line up parallel to the substrate.
IPS technology was developed by Hitachi and NEC. It was one of the first LCD technologies designed to smooth out the shortcomings of TN + film. But, despite expanding the viewing angle to 170 °, the rest of the functions did not budge. The response time of these displays varies from 50 to 60 ms, and the color display is mediocre.
If no voltage is applied to the IPS, then the liquid crystals will not rotate. The axis of polarization of the second filter is always perpendicular to the axis of the first, so that no light passes through in this situation. The screen exhibits an almost flawless black color. So in this area IPS has a clear advantage over TN + film displays - if the transistor burns out, the "dead" pixel will not be bright, but black. When voltage is applied to the subpixels, the two electrodes create an electric field and cause the crystals to rotate perpendicular to their previous position. After which the light can pass.
The worst thing is that creating an electric field in a system with such an arrangement of electrodes consumes a lot of energy, but even worse, it takes some time for the crystals to align. For this reason, IPS monitors often, if not always, have a longer response time than their TN + film counterparts.
On the other hand, precise crystal alignment improves the viewing angle.
MVA (Multi-Domain Vertical Alignment)
Some manufacturers prefer to use MVA, a technology developed by Fujitsu. According to them, MVA provides the best compromise for almost everything. Both the vertical and horizontal viewing angles are 160 °; response time is half that of IPS and TN + film - 25 ms; colors are displayed much more accurately. But why, if MVA has so many benefits, isn't it used universally? The point is, theory isn't that good in practice.
The MVA technology itself evolved from the VA introduced by Fujitsu in 1996. In such a system, the crystals without voltage supply are lined up vertically with respect to the second filter. Thus, light cannot pass through them. As soon as voltage is applied to them, the crystals rotate 90 °, letting in light and creating a bright spot on the screen.
The advantages of such a system are the speed and the absence of both a spiral structure and a double magnetic field. This reduced the response time to 25ms. Here you can also highlight the advantage that we already mentioned in IPS - very good black color. The main problem with the VA system was shade distortion when viewing the screen from an angle. If you display a pixel of any shade, for example, light red, then half the voltage will be applied to the transistor. In this case, the crystals will only rotate halfway. In front of the screen, you will see a light red color. However, if you look at the screen from the side, then in one case you will look along the direction of the crystals, and in the other - across. That is, you will see pure red on one side and pure black on the other.
So the company came to the need to solve the problem of distortion of shades and a year later, the MVA technology appeared.
This time, each subpixel was divided into several zones. Polarizer filters have also acquired a more complex structure, with bumpy electrodes. Crystals of each zone line up in their own direction, perpendicular to the electrodes. The task of this technology was to create the required number of zones so that the user always sees only one zone, no matter from what point on the screen he is looking.
Before buying a monitor
There are several factors you should consider when shopping.
The maximum viewing angle should be as large as possible, ideally more than or equal to 120 ° vertically (the horizontal angle is not so important).
While reaction times are often not specified, the shorter the better. The response time of the best modern LCD monitors is 25ms. But be careful, as this is where manufacturers are often cunning. Some indicate the on time and the off time of the pixel. If the on time is 15 ms and the off time is 25 ms, then the response time is 40 ms.
Contrast and brightness should be as high as possible - at least higher than 300: 1 and 200 cd / m2.
Another major problem with LCDs is dead pixels. Moreover, it is impossible to fix these light (TN + film) or dark "dead" pixels. Lying in the wrong places, dead pixels can get on your nerves. So before buying an LCD monitor, make sure there are no "dead" pixels, especially since a few "dead" pixels are not considered a defect.
Don't be fascinated by the vertical rotation of the display. Yes, indeed, you can rotate the display 90 °, but for a 15 "" monitor, this function is questionable, if not useless. You can use pivot in the following situations:
- creation office documents... Indeed, the pivot function can help a lot here;
- editing images that are larger in height than in width. However, CRT monitors are much better suited for image editing because they display true colors with the best level contrast;
- web browsing. The rotated 15 "" monitor has a horizontal resolution of 768 pixels. However, most web pages are designed for a resolution of at least 800 horizontal pixels.
Which monitor to buy: cathode ray tube (CRT) or liquid crystal (LCD)? It is widely believed that LCD monitors are "better in every way" and are much safer for the health of the user. And if financial possibilities allow, then it is necessary, unambiguously, to buy an LCD monitor.
There is some truth in these statements. The principle by which the image is formed on the LCD monitor is much more "friendly" for our eyes: dots on the screen of a cathode-ray tube "flash" when the scanning beam runs over them, and gradually fade out until the next run of the beam. Hence, the screen flickers at a low scan rate or at wrong setting video systems (i.e. complex: monitor + video card). In a liquid crystal monitor, each dot "glows" constantly and continuously, changing its color and brightness only when the corresponding command is received from the computer.
The scan line in a CRT monitor may be slightly displaced relative to the previous frame with each passage of the beam across the screen. This displacement may be due to a malfunction (or Low quality) of the monitor, and under the influence of external interference. The result is ripples on the screen, jitter or "floating" of the image. LCD monitors, in principle, are devoid of these drawbacks, since each point is located in a constant place.
No matter how great the anti-reflective coating is applied to the glass screen of a cathode ray tube, glare and reflections cannot be completely eliminated. The screens of liquid crystal monitors reflect light much weaker already due to their design and the materials used, so there is practically no glare on them.
Finally, the level of all types of radiation in LCD monitors is much lower: after all, the main source of radiation, electromagnetic and electrostatic fields is a cathode ray tube, which is absent in a liquid crystal monitor as such.
But not everything is so simple... There are many situations where a CRT monitor would be preferable.
The pixel dimensions of even very good LCD monitors are still larger than even average CRTs. Therefore, the clarity of the fine details of the image on the LCD monitor is insufficient.
So far, the developers of LCD monitors have not been able to achieve high-quality color reproduction, especially light tones, and high image contrast. Even the most expensive and sophisticated LCD monitors lose in these parameters to most simple and cheap CRT monitors.
The angle of view, that is, the angle at which we can normally see the image on the screen, in LCD monitors is much smaller than in monitors with a cathode ray tube.
LCD monitors very noticeably lose image quality if you switch them from their "native" ("optimal", "manufacturer's recommended") screen resolution to another.
Finally, liquid crystal monitors are characterized by some inertia of the image: with very dynamic "pictures", for example, during video playback or in "high-speed" games, the "slowdown" of the image is often noticeable "with the naked eye."
Actually, listing the above disadvantages of LCD monitors, one could begin each paragraph with the phrase: "So far, the developers of LCD monitors have not been able to achieve ... this ... and that ...". With an emphasis on the words "For now". It is quite possible that, rereading this page in 2-3 years, you will be grinning at what is written here. But now, in 2005, the situation is exactly that.
Summarizing all of the above, we can give such recommendations.
An LCD monitor is best purchased if:
- you work mainly with textual information;
- your workplace has poor lighting conditions, it is difficult to avoid glare and reflections;
- the monitor will be installed in an area with strong electromagnetic interference, for example, near a power cable;
- the monitor will be used by children.
And it is better to buy a monitor with a cathode-ray tube if:
- you are a designer or constructor, that is, you work mainly with graphics, moreover complex, rich in small details; high-quality color rendition is important to you, especially halftones and shades;
- you assume frequent joint work behind this monitor or are going to use it for some kind of displays, presentations, that is, if situations arise regularly when the image on the monitor screen will need to be seen by many people at the same time;
- you work with frequently changing, dynamic pictures, for example, you are editing (or watching) a video. Or like to play all sorts of shooting races;
- if you have high or moderate myopia.
For the past few years, looking to purchase a monitor for an office or home computer, were at a crossroads - should you choose an LCD or CRT monitor? CRT devices have long been favored by users, aided by the “smearing effect” of the image on the LCD screen. But the problem was resolved, and this year the situation has changed dramatically. LCDs are actively pushing their CRT counterparts in the monitor market and winning the hearts of TV buyers. Leading companies in digital signal processing, based on customer preferences and trends in technology and the market, believe that the future belongs to LCD panels, which will later become universal (TV and monitor in one "package").
CRT monitors have no advantage
There were plenty of arguments in favor of purchasing a display with a traditional cathode ray tube (CRT) a few years ago - better color rendering, a larger viewing angle, and higher contrast. In addition, the prices for these monitors have been steadily decreasing.
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If a few years ago you had to spend more than $ 300 for a 15-inch CRT monitor, now for the same money you can buy a good 19-inch display from such well-known manufacturers (and not fear for the quality) such as Phillips, Samsung or ViewSonic.
Of course, the consumer continues to be embarrassed by conversations (which have a very real basis) about increased electromagnetic radiation, causing irreparable damage to health, as well as an extremely cumbersome purchase: a CRT display can weigh tens of kilograms and take up a significant part even on an extensive desktop.
Initially, there was very little rationale for an LCD display. In addition to the absence of harmful radiation exposure, the buyer was, of course, attracted by its small dimensions.
The LCD monitor discreetly nestles on the edge of a desk and leaves ample room for more and more computer accessories. But in all other parameters - brightness, contrast, recall speed, color rendering - LCD monitors for a long time were significantly inferior to their large and heavy "tubular" counterparts.
Dmitry Kravchenko, Components and Peripheral Equipment Manager at Acer CIS Inc.
CNews.ru: How dynamically is the Russian market of LCD monitors developing?
It is safe to say that the market for LCD monitors in Russia is developing “explosively”. Private companies and home users have practically stopped purchasing traditional CRT monitors with new computers due to the obvious advantages of LCD technology over CRT. In addition, there is a huge market for CRT to LCD upgrades.
CNews.ru: How dynamically is the Russian market of LCD monitors developing? What directions in the Russian market of LCD monitors can be called promising for the next year or two?
Promising directions monitor market for home and SOHO users can be considered traditional and widescreen LCD monitors with large diagonal screen and a variety of interfaces (analog, DVI, AV), with fast, bright and high-contrast LCD panels. Such devices are ready for media convergence and should be in demand for this reason. For the corporate market, 17-inch traditional LCD monitors seem to be the most promising. they are optimal in terms of return on investment (ROI), as well as because this is a trend in the European and world markets and that the Russian market cannot stand aside.
CNews.ru: What is the share of the public sector and private companies among consumers of LCD displays in Russia? How does the situation on the Russian market differ from that on the Eastern and Western European markets?
The share of the public sector is still minimal, but there is also a tendency to switch demand from CRT to LCD technology. The Russian market for LCD monitors lags behind the Western European market for economic reasons, but belatedly repeats the trends and patterns of the European market.
CNews.ru: How do you assess the prospects for the development of the Russian laptop market (they have an LCD screen) due to the fact that LCD screens are gradually becoming cheaper, and their quality has improved significantly over the past year and a half?
I assess the prospects for the development of the Russian laptop market as the most optimistic for the reasons mentioned in the question, and also because the main advantage of laptops compared to desktop PCs is mobility, and therefore becomes available to an increasingly wider masses of users. This should lead to explosive growth in the mobile PC market. The situation will be similar to that observed in the market mobile communications, when mobile phone has become affordable for many.
CNews.ru: What changes can occur in the LCD panel market in connection with the active expansion of new models, where the problem of the “smearing effect” of the image on the LCD screen has been solved?
In addition to the answer given above (see question 2 - CNews), it should be noted that 15-inch LCD monitors will remain the most popular segment in the Russian market for LCD monitors for some time as the most attractive in terms of price.
CNews.ru: What changes in everyday life and in the structure of the market as a whole will result from the "splicing" of LCD monitors and LCD TV?
As long as LCD TVs are significantly more expensive than CRT TVs with a comparable screen size, there will be no significant changes in the structure of the consumer TV market. At the same time, the "splicing" of LCD monitors and LCD TV should lead to a decrease in the cost of LCD TV, since the sales channel of IT products is more dynamic than the sales channel. household appliances... Also, the aforementioned splicing will drive the growth of the PC-based media center market.
CNews.ru: Thank you.
The last few years have not been in vain. The world's leading manufacturers did not stand still and were constantly working to improve the characteristics of such displays, and the price for them has dropped significantly in the last year and a half. As a result, now the problem of choosing a monitor has become extremely aggravated.
However, this applies not only to Russian users. American and European consumers have long struggled to determine their preferences, and computer market research companies have been keeping a close eye on which trends will prevail.
Just a couple of years ago, LCD monitors in Europe accounted for about 10% of the market. Experts believed that they will not be able to win the sympathy of users any time soon.
This year, however, there was a rather sudden turn in the mood of European consumers - they drastically reduced purchases of CRT displays, making the volume of sales of LCD monitors for the first time exceeding the sales of their counterparts with a cathode ray tube.
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The accelerated growth of interest in the new generation of displays is driven by several factors. For the corporate sector, an important circumstance is that LCD monitors consume significantly less power. When these monitors sit on the desks of hundreds of employees, the savings can be quite substantial for the company.
A consumer buying a monitor for home use, attracted by the fact that, finally, it can be comfortably used for 3D games. Most modern 15-inch models now have a response time of 25 ms, which has led to the disappearance of the "blur effect" of the image on the screen.
The horizontal viewing angle has increased to 120-150 degrees, which means that not only the player sitting directly in front of the monitor can watch what is happening on the screen. In addition, the main resolution of the 15-inch LCD (1024x768) makes it possible to play both old games made in 800x600 resolution, as well as practically any new games.
Another important factor that determines the choice of the consumer is the process of convergence of a computer monitor and a TV set. Everything appears on sale more monitors, which have a built-in TV tuner, connectors such as "scart" or "tulip", remote control.
Such a device ceases to be a monofunctional attachment to a computer and acquires an independent value, which makes it more desirable for all family members. As a result, the purchase of an LCD display is becoming more and more justified, and manufacturing firms have sensed this trend in increased sales.
It is noteworthy that at this year's Internationale Funk-ausstellung (IFA) held in Berlin this year, leading TV manufacturers almost unanimously said that the future lies with LCD technology. Thus, according to the forecasts of the research company Display Search, in 2005 the world will sell from 12 to 13 million TV sets with LCD screens.
Leading companies in digital signal processing (having invested money in this direction for a long time) are now intensively expanding old and opening new production of LCD TVs and monitors (for the time being, these devices are positioned separately, as intended for different market segments). For example, Motorola, after an almost 30-year hiatus (it was a pioneer in the American TV market and exited the business in 1974), is resuming TV production, but now with an LCD screen.
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The chart below shows the sales of 10 well-known display manufacturers who were able to sell over 100,000 LCD monitors each in the European market in the second quarter of 2003.
(on the European market in 2Q 2003)
→ LCD vs CRT
At one time, faced with the problem of visual impairment, I began to look for the reason for this state of affairs. Chronologically, the deterioration coincided in time with the replacement of the old 15-inch Samsung 550b monitor with the Samsung 730bf LCD fancy at that time.
First new monitor I liked it very much: flat, wide (3 "more than 15-scale, which has a real visible area of 14"), eats little electricity, looks much better on the table.
The joy was quickly interrupted after the first hour of work with a new monitor (I think this is familiar to most of those who switched from CRT on LCD). Everything would be fine, but the image is “somehow not like that”, it’s like “ cuts eyes».
The first thing I started to blame was the monitor settings. What I just didn’t twist, switched the temperature, changed the brightness, contrast, even tried to change the cable. The result is the same - 3 hours of work and eyes in a bunch, watery, hurt.
I got used to it, after 2 weeks. If it was still in games, it was still difficult to read the text on a white background.
Time passed and after half a year I started having problems with my eyes. I noticed that my vision began to deteriorate, and it fluctuated (in the morning it was better, and in the late afternoon it worsened). I began to sin on general fatigue (student, exercise machine, in the evening in the park) - constant lack of sleep. But to the point, the situation did not improve.
Of course, I cannot say with 100% certainty that the cause of the problems that began was precisely eye fatigue from the LCD monitor, which later grew into dry eyes and all the ensuing consequences. But the fact that I sat behind my 15th grade from the 10th grade to the 4th year of the university (and in general I have been dealing with computers from the 7th grade) and did not know what fatigue is or what bad eyesight (although I could sit a day for 10 and 12 hours) is a fact.
This one alarmed me. I became interested in the question “ Are LCD monitors as safe as they say?", Because theoretically they have all the same drawbacks as conventional CRTs (image pixelity, flicker frequency, flat picture, light falling into the eyes, etc.).
I started looking for an answer on the Internet, and ... and found some very interesting data.
Theoretically, if you think about it .. if there were no problem, 177 moderated pages (as of 22.30.09) with 20 posts each would not have come from the air. So the problem exists, and it is serous.
I am sure to re-read all 177 pages you are unlikely to have a desire, nevertheless I (at least 80% percent) re-read all the posts, even with interest. And came to some conclusions:
1. The so-called the problem of "LCD monitors" not fiction. It exists and many quite adequate people feel discomfort to one degree or another (from slight eye fatigue to almost complete inability to work) with TFT monitors, while working without problems with CRTs of different models and levels for years. But for many, this manifests itself (does not manifest itself) in completely different degrees. But to say that more than 100 people (approximately that many I counted only those who unsubscribed in the corresponding branches on the iXBT forum and overclockers.ru) are wrong, I think it would be wrong.
2. This problem is systemic, associated with the technology of image formation on modern TFT monitors. I will not go into details, but the increased brightness can be attributed here, and ultraviolet emitted by gas-discharge mercury backlight lamps, and PWM sweep frequency lamp supply that fluctuates widely from model to model (150 Hz to 500 Hz), and quality of the element base in general, modern monitors (including the matrix), interpixel flicker and many other factors.
To see if my words make sense or not, do the following:
- observe yourself, if you feel tired while working at the LCD monitor, if your eyes dry while working, if your head hurts, fatigue may appear;
- open any document (notebook or browser with a blank page) with a white background turned on, brightness and contrast can be removed to almost zero - or set the one you are used to working with.
Print a small black line in the center of the screen in a small font size. Try to concentrate on the line, read it a couple of times. In most cases, after a while (from a couple of seconds to a few minutes), you will begin to experience discomfort. Now move your eyes from the monitor, say to the printer, then repeat back. When you remove your gaze - your eyes seem to be resting, move them back - as if they are trying to strain;
- LCD monitors have a so-called " interpixel flicker"(Conditionally), which also does not have the best effect on the comfort of work. More details about this effect can be found here at this link - http://www.techmind.org/lcd/.
The site above says something like this:
To change the light conductivity, a voltage is applied to the “pixel” (without going into the intricacies of the implementation), while the conductivity is affected only by absolute value but not polarity. The voltage conductivity characteristic is symmetrical about zero potential.
Further, the authors write: “in order to prevent polarization, and a defect in the liquid crystal material, the voltage polarity is reversed on“ alternative video frames ”, probably something like“ negative-polar video frames ”is meant. Then it is argued that it is very difficult to obtain the same voltage of different polarity (and it is possible that the characteristic is simply not symmetrical), and therefore the effect of flickering of the entire screen with a frequency of half the frame rate, that is, about 30 Hz…
Further it comes that if you change the polarity at once for the entire screen, then this flicker is visible very strongly, so they do in the following way- in antiphase, only the voltage of neighboring pixels, located in matrices of different designs, changes according to a certain law.
Further, on the same site there are links to specially formed pages (using simple HTML, you can use any browser in full screen mode), with an image such that only the points of one phase are highlighted. From a dozen links, you need to choose the one on which the screen will flicker. It also shows the order in which the pixels for this picture are located, and if the screen flickers, then this is your type of matrix.
I personally checked it on several monitors - they all flicker.
That is, in fact, we have a blinker that flickers depending on the type of image and, with varying intensity from temperature. The very fact of what is already alarming.
The worst part is that manufacturers don't want to see this problem at all. Since with CRT monitors it is quite rightly done, then there is practically no alternative for people experiencing problems with modern TFTs.
Finally
Again, I am not saying that LCD monitors are evil, but CRTs are "rules" and the eyes do not get tired behind them. No. I simply state, from my own experience, that “ LCDs are not harmless"(As many write about it, they say that your eyes hurt - buy a TFT) that they have their drawbacks and for a certain percentage of people they are even harmful. What is the reason for this state of affairs is unknown, and we will hardly ever find out. What is the reason for manufacturers of LCD monitors to conduct research on the dangers of their products?
Today I sit in front of a Neovo E19A monitor with a NeoV glass filter (it is 3mm glass in front of the matrix and theoretically makes the image softer and slightly changes the light spectrum - a kind of computer glasses, only on the entire surface of the screen), while working in computer glasses , doing exercises and trying to rest more.
This does not save me from problems - I got asthenopia and permanent dry eyes, but the fact is that with this monitor I am able to work much longer, and the image is softer and more pleasant (white at a distance of 50-60 cm, the pixel grid is practically invisible).
It would seem that two absolutely similar TFT monitors Samsung 730bf and Neovo E19A are made theoretically using the same technologies, with the same type of matrix (TN), and for one I can sit for a maximum of 3-4 hours, and after another 8-9 is not a problem, and this is already existing eye problems.
My wishes for you: take a responsible attitude to the choice and purchase of a monitor, try the monitor in operation and only after that buy it. Maybe new types of matrices or new backlighting mechanisms (possibly external backlighting) will be a salvation, but so far there is only the fact that displays are harmful, be it a new TFT or an old CRT.
Best wishes to you.