tft lcd led unterschied quotation

IPS (In-Plane Switching) lcd is still a type of TFT LCD, IPS TFT is also called SFT LCD (supper fine tft ),different to regular tft in TN (Twisted Nematic) mode, theIPS LCD liquid crystal elements inside the tft lcd cell, they are arrayed in plane inside the lcd cell when power off, so the light can not transmit it via theIPS lcdwhen power off, When power on, the liquid crystal elements inside the IPS tft would switch in a small angle, then the light would go through the IPS lcd display, then the display on since light go through the IPS display, the switching angle is related to the input power, the switch angle is related to the input power value of IPS LCD, the more switch angle, the more light would transmit the IPS LCD, we call it negative display mode.

The regular tft lcd, it is a-si TN (Twisted Nematic) tft lcd, its liquid crystal elements are arrayed in vertical type, the light could transmit the regularTFT LCDwhen power off. When power on, the liquid crystal twist in some angle, then it block the light transmit the tft lcd, then make the display elements display on by this way, the liquid crystal twist angle is also related to the input power, the more twist angle, the more light would be blocked by the tft lcd, it is tft lcd working mode.

A TFT lcd display is vivid and colorful than a common monochrome lcd display. TFT refreshes more quickly response than a monochrome LCD display and shows motion more smoothly. TFT displays use more electricity in driving than monochrome LCD screens, so they not only cost more in the first place, but they are also more expensive to drive tft lcd screen.The two most common types of TFT LCDs are IPS and TN displays.

Key Difference: LCDs are a type of television screen that uses liquid crystals sandwiched between two sheets of polarizing material. TFT (Thin-film transistor) is a field-effect transistor that is used to build the LCD screen and is embedded in every pixel, making it faster and giving a better image quality.

An LCD is type of television screen that uses liquid crystals sandwiched between two sheets of polarizing material. LCDs are used in TVs, computer monitors, clocks, calculators, cell phones, etc. LCDs provide significant benefits compared to CRTs and plasmas, such as they consume less power than both. Both CRTs and Plasmas are susceptible to burn-ins while LCDs are not. However, LCDs require a backlight as it does not emit light by itself.

In market, LCD means passive matrix LCDs which increase TN (Twisted Nematic), STN (Super Twisted Nematic), or FSTN (Film Compensated STN) LCD Displays. It is a kind of earliest and lowest cost display technology.

LCD screens are still found in the market of low cost watches, calculators, clocks, utility meters etc. because of its advantages of low cost, fast response time (speed), wide temperature range,  low power consumption, sunlight readable with transflective or reflective polarizers etc.  Most of them are monochrome LCD display and belong to passive-matrix LCDs.

TFT LCDs have capacitors and transistors. These are the two elements that play a key part in ensuring that the TFT display monitor functions by using a very small amount of energy without running out of operation.

Normally, we say TFT LCD panels or TFT screens, we mean they are TN (Twisted Nematic) Type TFT displays or TN panels, or TN screen technology. TFT is active-matrix LCDs, it is a kind of LCD technologies.

TFT has wider viewing angles, better contrast ratio than TN displays. TFT display technologies have been widely used for computer monitors, laptops, medical monitors, industrial monitors, ATM, point of sales etc.

Actually, IPS technology is a kind of TFT display with thin film transistors for individual pixels. But IPS displays have superior high contrast, wide viewing angle, color reproduction, image quality etc. IPS screens have been found in high-end applications, like Apple iPhones, iPads, Samsung mobile phones, more expensive LCD monitors etc.

Both TFT LCD displays and IPS LCD displays are active matrix displays, neither of them can produce color, there is a layer of RGB (red, green, blue) color filter in each LCD pixels to make LCD showing colors. If you use a magnifier to see your monitor, you will see RGB color. With switch on/off and different level of brightness RGB, we can get many colors.

Neither of them can’t release color themselves, they have relied on extra light source in order to display. LED backlights are usually be together with them in the display modules as the light sources. Besides, both TFT screens and IPS screens are transmissive, it will need more power or more expensive than passive matrix LCD screens to be seen under sunlight.  IPS screens transmittance is lower than TFT screens, more power is needed for IPS LCD display.

A thin-film-transistor liquid-crystal display (TFT LCD) is a variant of a liquid-crystal display that uses thin-film-transistor technologyactive matrix LCD, in contrast to passive matrix LCDs or simple, direct-driven (i.e. with segments directly connected to electronics outside the LCD) LCDs with a few segments.

In February 1957, John Wallmark of RCA filed a patent for a thin film MOSFET. Paul K. Weimer, also of RCA implemented Wallmark"s ideas and developed the thin-film transistor (TFT) in 1962, a type of MOSFET distinct from the standard bulk MOSFET. It was made with thin films of cadmium selenide and cadmium sulfide. The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968. In 1971, Lechner, F. J. Marlowe, E. O. Nester and J. Tults demonstrated a 2-by-18 matrix display driven by a hybrid circuit using the dynamic scattering mode of LCDs.T. Peter Brody, J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories developed a CdSe (cadmium selenide) TFT, which they used to demonstrate the first CdSe thin-film-transistor liquid-crystal display (TFT LCD).active-matrix liquid-crystal display (AM LCD) using CdSe TFTs in 1974, and then Brody coined the term "active matrix" in 1975.high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.

The circuit layout process of a TFT-LCD is very similar to that of semiconductor products. However, rather than fabricating the transistors from silicon, that is formed into a crystalline silicon wafer, they are made from a thin film of amorphous silicon that is deposited on a glass panel. The silicon layer for TFT-LCDs is typically deposited using the PECVD process.

Polycrystalline silicon is sometimes used in displays requiring higher TFT performance. Examples include small high-resolution displays such as those found in projectors or viewfinders. Amorphous silicon-based TFTs are by far the most common, due to their lower production cost, whereas polycrystalline silicon TFTs are more costly and much more difficult to produce.

The twisted nematic display is one of the oldest and frequently cheapest kind of LCD display technologies available. TN displays benefit from fast pixel response times and less smearing than other LCD display technology, but suffer from poor color reproduction and limited viewing angles, especially in the vertical direction. Colors will shift, potentially to the point of completely inverting, when viewed at an angle that is not perpendicular to the display. Modern, high end consumer products have developed methods to overcome the technology"s shortcomings, such as RTC (Response Time Compensation / Overdrive) technologies. Modern TN displays can look significantly better than older TN displays from decades earlier, but overall TN has inferior viewing angles and poor color in comparison to other technology.

Most TN panels can represent colors using only six bits per RGB channel, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bit truecolor) that are available using 24-bit color. Instead, these panels display interpolated 24-bit color using a dithering method that combines adjacent pixels to simulate the desired shade. They can also use a form of temporal dithering called Frame Rate Control (FRC), which cycles between different shades with each new frame to simulate an intermediate shade. Such 18 bit panels with dithering are sometimes advertised as having "16.2 million colors". These color simulation methods are noticeable to many people and highly bothersome to some.gamut (often referred to as a percentage of the NTSC 1953 color gamut) are also due to backlighting technology. It is not uncommon for older displays to range from 10% to 26% of the NTSC color gamut, whereas other kind of displays, utilizing more complicated CCFL or LED phosphor formulations or RGB LED backlights, may extend past 100% of the NTSC color gamut, a difference quite perceivable by the human eye.

The transmittance of a pixel of an LCD panel typically does not change linearly with the applied voltage,sRGB standard for computer monitors requires a specific nonlinear dependence of the amount of emitted light as a function of the RGB value.

Less expensive PVA panels often use dithering and FRC, whereas super-PVA (S-PVA) panels all use at least 8 bits per color component and do not use color simulation methods.BRAVIA LCD TVs offer 10-bit and xvYCC color support, for example, the Bravia X4500 series. S-PVA also offers fast response times using modern RTC technologies.

When the field is on, the liquid crystal molecules start to tilt towards the center of the sub-pixels because of the electric field; as a result, a continuous pinwheel alignment (CPA) is formed; the azimuthal angle rotates 360 degrees continuously resulting in an excellent viewing angle. The ASV mode is also called CPA mode.

TFT dual-transistor pixel or cell technology is a reflective-display technology for use in very-low-power-consumption applications such as electronic shelf labels (ESL), digital watches, or metering. DTP involves adding a secondary transistor gate in the single TFT cell to maintain the display of a pixel during a period of 1s without loss of image or without degrading the TFT transistors over time. By slowing the refresh rate of the standard frequency from 60 Hz to 1 Hz, DTP claims to increase the power efficiency by multiple orders of magnitude.

Due to the very high cost of building TFT factories, there are few major OEM panel vendors for large display panels. The glass panel suppliers are as follows:

External consumer display devices like a TFT LCD feature one or more analog VGA, DVI, HDMI, or DisplayPort interface, with many featuring a selection of these interfaces. Inside external display devices there is a controller board that will convert the video signal using color mapping and image scaling usually employing the discrete cosine transform (DCT) in order to convert any video source like CVBS, VGA, DVI, HDMI, etc. into digital RGB at the native resolution of the display panel. In a laptop the graphics chip will directly produce a signal suitable for connection to the built-in TFT display. A control mechanism for the backlight is usually included on the same controller board.

The low level interface of STN, DSTN, or TFT display panels use either single ended TTL 5 V signal for older displays or TTL 3.3 V for slightly newer displays that transmits the pixel clock, horizontal sync, vertical sync, digital red, digital green, digital blue in parallel. Some models (for example the AT070TN92) also feature input/display enable, horizontal scan direction and vertical scan direction signals.

New and large (>15") TFT displays often use LVDS signaling that transmits the same contents as the parallel interface (Hsync, Vsync, RGB) but will put control and RGB bits into a number of serial transmission lines synchronized to a clock whose rate is equal to the pixel rate. LVDS transmits seven bits per clock per data line, with six bits being data and one bit used to signal if the other six bits need to be inverted in order to maintain DC balance. Low-cost TFT displays often have three data lines and therefore only directly support 18 bits per pixel. Upscale displays have four or five data lines to support 24 bits per pixel (truecolor) or 30 bits per pixel respectively. Panel manufacturers are slowly replacing LVDS with Internal DisplayPort and Embedded DisplayPort, which allow sixfold reduction of the number of differential pairs.

Backlight intensity is usually controlled by varying a few volts DC, or generating a PWM signal, or adjusting a potentiometer or simply fixed. This in turn controls a high-voltage (1.3 kV) DC-AC inverter or a matrix of LEDs. The method to control the intensity of LED is to pulse them with PWM which can be source of harmonic flicker.

Kawamoto, H. (2012). "The Inventors of TFT Active-Matrix LCD Receive the 2011 IEEE Nishizawa Medal". Journal of Display Technology. 8 (1): 3–4. Bibcode:2012JDisT...8....3K. doi:10.1109/JDT.2011.2177740. ISSN 1551-319X.

K. H. Lee; H. Y. Kim; K. H. Park; S. J. Jang; I. C. Park & J. Y. Lee (June 2006). "A Novel Outdoor Readability of Portable TFT-LCD with AFFS Technology". SID Symposium Digest of Technical Papers. AIP. 37 (1): 1079–82. doi:10.1889/1.2433159. S2CID 129569963.

All displays work in a similar manner. In a very basic explanation, they all have many rows and columns of pixels driven by a controller that communicates with each pixel to emit the brightness and color needed to make up the transmitted image. In some devices, the pixels are diodes that light up when current flows (PMOLEDs and AMOLEDs), and in other electronics, the pixel acts as a shutter to let some of the light from a backlight visible. In all cases, a memory array stores the image information that travels to the display through an interface.

Serial Peripheral Interface (SPI) is a synchronous serial communication interface best-suited for short distances. It was developed by Motorola for components to share data such as flash memory, sensors, Real-Time Clocks, analog-to-digital converters, and more. Because there is no protocol overhead, the transmission runs at relatively high speeds. SPI runs on one master (the side that generates the clock) with one or more slaves, usually the devices outside the central processor. One drawback of SPI is the number of pins required between devices. Each slave added to the master/slave system needs an additional chip select I/O pin on the master. SPI is a great option for small, low-resolution displays including PMOLEDs and smaller LCDs.

Philips Semiconductors invented I2C (Inter-integrated Circuit) or I-squared-C in 1982. It utilizes a multi-master, multi-slave, single-ended, serial computer bus system. Engineers developed I2C for simple peripherals on PCs, like keyboards and mice to then later apply it to displays. Like SPI, it only works for short distances within a device and uses an asynchronous serial port. What sets I2C apart from SPI is that it can support up to 1008 slaves and only requires two wires, serial clock (SCL), and serial data (SDA). Like SPI, I2C also works well with PMOLEDs and smaller LCDs. Many display systems transfer the touch sensor data through I2C.

Low-Voltage Differential Signaling (LVDS) was developed in 1994 and is a popular choice for large LCDs and peripherals in need of high bandwidth, like high-definition graphics and fast frame rates. It is a great solution because of its high speed of data transmission while using low voltage. Two wires carry the signal,  with one wire carrying the exact inverse of its companion. The electric field generated by one wire is neatly concealed by the other, creating much less interference to nearby wireless systems. At the receiver end, a circuit reads the difference (hence the "differential" in the name) in voltage between the wires. As a result, this scheme doesn’t generate noise or gets its signals scrambled by external noise. The interface consists of four, six, or eight pairs of wires, plus a pair carrying the clock and some ground wires. 24-bit color information at the transmitter end is converted to serial information, transmitted quickly over these pairs of cables, then converted back to 24-bit parallel in the receiver, resulting in an interface that is very fast to handle large displays and is very immune to interference.

Mobile Industry Processor Interface (MIPI) is a newer technology that is managed by the MIPI Alliance and has become a popular choice among wearable and mobile developers. MIPI uses similar differential signaling to LVDS by using a clock pair and one to eight pairs of data called lanes. MIPI supports a complex protocol that allows high speed and low power modes, as well as the ability to read data back from the display at lower rates. There are several versions of MIPI for different applications, MIPI DSI being the one for displays.

To give an example, a small monochrome PMOLED with a resolution of 128 x 128 contains 16,384 individual diodes. A still image of various diodes carrying current represents a frame. A frame rate is the number of times that a picture needs refreshing. Most videos have a frame rate of 60 fps (frames per second), which means that it is updated 60 times every second.

Take the same PMOLED display with the 128 x 128 resolution and 16,384 separate diodes; it requires information as to when and how brightly to illuminate each pixel. For a display with only 16 shades, it takes 4 bits of data. 128 x 128 x 4 = 65,536 bits for one frame. Now multiply it by the 60Hz, and you get a bandwidth of 4 megabits/second for a small monochrome display.

Compared with ordinary LCDs, TFT LCDs provide very clear images/text with shorter response times. TFT LCDs are increasingly being used to bring better visual effects to products.

TFT stands for “thin film transistor”. The transistor of a color TFT LCD is composed of a thin film of amorphous silicon deposited on glass. It acts as a control valve to provide the appropriate voltage to the liquid crystal for each sub-pixel. This is why TFT LCDs are also known as active matrix displays.

TFT LCDs have a liquid crystal layer between a glass substrate formed by the TFT and transparent pixel electrodes and another glass substrate with a color filter (RGB) and a transparent counter electrode. Each pixel in the active matrix is paired with a transistor that includes a capacitor, which gives each sub-pixel the ability to retain its charge without sending a charge every time it needs to be replaced. This means that TFT LCDs are more responsive.

To understand how a TFT LCD works, we must first grasp the concept of a field effect transistor (FET), which is a transistor that uses an electric field to control the flow of current. It is a component with three terminals: source, gate and drain. fet controls the flow of current by applying a voltage to the gate, thereby changing the conductivity between the drain and source.

Using the FET, we can build a circuit as follows. The data bus sends a signal to the source of the FET, and when SEL SIGNAL applies a voltage to the gate, a drive voltage is generated on the TFT LCD panel. A sub-pixel is lit. A TFT LCD display contains thousands or millions of such driver circuits.

Color TFT LCD from 1.8 inch ~ 15 inch, there are different resolutions and interfaces. How to choose the right TFT LCD, you can refer to the previous article “LCD | How to choose a liquid crystal display module

In one corner is LED (light-emitting diode). It’s the most common type of display on the market, however, it might be unfamiliar because there’s slight labelling confusion with LCD (liquid crystal display).

For display purposes the two are the same, and if you see a TV or smartphone that states it has an ‘LED’ screen, it’s an LCD. The LED part just refers to the lighting source, not the display itself.

In a nutshell, LED LCD screens use a backlight to illuminate their pixels, while OLED’s pixels produce their own light. You might hear OLED’s pixels called ‘self-emissive’, while LCD tech is ‘transmissive’.

The light of an OLED display can be controlled on a pixel-by-pixel basis. This sort of dexterity isn’t possible with an LED LCD – but there are drawbacks to this approach, which we’ll come to later.

In cheaper TVs and LCD-screen phones, LED LCD displays tend to use ‘edge lighting’, where LEDs sit to the side of the display, not behind it. The light from these LEDs is fired through a matrix that feeds it through the red, green and blue pixels and into our eyes.

LED LCD screens can go brighter than OLED. That’s a big deal in the TV world, but even more so for smartphones, which are often used outdoors and in bright sunlight.

Take an LCD screen into a darkened room and you may notice that parts of a purely black image aren’t black, because you can still see the backlighting (or edge lighting) showing through.

You’ll often see a contrast ratio quoted in a product’s specification, particularly when it comes to TVs and monitors. This tells you how much brighter a display’s whites are compared to its blacks. A decent LCD screen might have a contrast ratio of 1,000:1, which means the whites are a thousand times brighter than the blacks.

Contrast on an OLED display is far higher. When an OLED screen goes black, its pixels produce no light whatsoever. That means an infinite contrast ratio, although how great it looks will depend on how bright the screen can go. In general, OLED screens are best suited for use in darker rooms, and this is certainly the case where TVs are concerned.

OLED panels enjoy excellent viewing angles, primarily because the technology is so thin, and the pixels are so close to the surface. You can walk around an OLED TV or spread out in different spots in your living room, and you won’t lose out on contrast. For phones, viewing angles are extra important because you don’t tend to hold your hand perfectly parallel to your face.

Viewing angles are generally worse in LCDs, but this varies hugely depending on the display technology used. And there are lots of different kinds of LCD panel.

Perhaps the most basic is twisted nematic (TN). This is the type used in budget computer monitors, cheaper laptops, and very low-cost phones, and it offers poor angled viewing. If you’ve ever noticed that your computer screen looks all shadowy from a certain angle, it’s more than likely it uses a twisted nematic panel.

Thankfully, a lot of LCD devices use IPS panels these days. This stands for ‘in-plane switching’ and it generally provides better colour performance and dramatically improved viewing angles.

IPS is used in most smartphones and tablets, plenty of computer monitors and lots of TVs. It’s important to note that IPS and LED LCD aren’t mutually exclusive; it’s just another bit of jargon to tack on. Beware of the marketing blurb and head straight to the spec sheet.

The latest LCD screens can produce fantastic natural-looking colours. However, as is the case with viewing angles, it depends on the specific technology used.

OLED’s colours have fewer issues with pop and vibrancy, but early OLED TVs and phones had problems reining in colours and keeping them realistic. These days, the situation is better, Panasonic’s flagship OLEDs are used in the grading of Hollywood films.

Where OLED struggles is in colour volume. That is, bright scenes may challenge an OLED panel’s ability to maintain levels of colour saturation. It’s a weakness that LCD-favouring manufacturers enjoy pointing out.

Both have been the subject of further advancements in recent years. For LCD there’s Quantum Dot and Mini LED. The former uses a quantum-dot screen with blue LEDs rather than white LEDs and ‘nanocrystals’ of various sizes to convert light into different colours by altering its wavelength. Several TV manufacturers have jumped onboard Quantum Dot technology, but the most popular has been Samsung’s QLED branded TVs.

Mini LED is another derivation of LED LCD panels, employing smaller-sized LEDs that can emit more light than standard versions, increasing brightness output of the TV. And as they are smaller, more can be fitted into a screen, leading to greater control over brightness and contrast. This type of TV is becoming more popular, though in the UK and Europe it’s still relatively expensive. You can read more about Mini LED and its advantages in our explainer.

OLED, meanwhile, hasn’t stood still either. LG is the biggest manufacturer of large-sized OLED panels and has produced panels branded as evo OLED that are brighter than older versions. It uses a different material for its blue OLED material layer within the panel (deuterium), which can last for longer and can have more electrical current passed through it, increasing the brightness of the screen, and elevating the colour volume (range of colours it can display).

Another development is the eagerly anticipated QD-OLED. This display technology merges Quantum Dot backlights with an OLED panel, increasing the brightness, colour accuracy and volume, while retaining OLED’s perfect blacks, infinite contrast and potentially even wider viewing angles, so viewers can spread out anywhere in a room and see pretty much the same image. Samsung and Sonyare the two companies launching QD-OLED TVs in 2022.

And for smartphones there’s been a move towards AMOLED (Active-Matrix Organic Light Emitting Diode) screens for Android screens, while Apple has moved towards OLED for its smartphones and tried Mini LED with its iPad Pro. Technologies are consistently evolving with Superand Dynamic AMOLED versions available, more performance is being eked out.

While LED LCD has been around for much longer and is cheaper to make, manufacturers are beginning to move away from it, at least in the sense of the ‘standard’ LCD LED displays, opting to explore the likes of Mini LED and Quantum Dot variations.

OLED has gained momentum and become cheaper, with prices dipping well below the £1000 price point. OLED is much better than LED LCD at handling darkness and lighting precision, and offers much wider viewing angles, which is great for when large groups of people are watching TV. Refresh rates and motion processing are also better with OLED though there is the spectre of image retention.

If you’re dealing with a limited budget, whether you’re buying a phone, a monitor, a laptop or a TV, you’ll almost certainly end up with an LCD-based screen. OLED, meanwhile, incurs more of a premium but is getting cheaper, appearing in handheld gaming devices, laptops, some of the best smartphones as well as TVs

Which is better? Even if you eliminate money from the equation, it really comes down to personal taste. Neither OLED nor LCD LED is perfect. Some extol OLED’s skill in handling darkness, and its lighting precision. Others prefer LCD’s ability to go brighter and maintain colours at bright levels.

How do you decide? Stop reading this and go to a shop to check it out for yourself. While a shop floor isn’t the best environment in which to evaluate ultimate picture quality, it will at least provide an opportunity for you to realise your priorities. Whether you choose to side with LCD or OLED, you can take comfort in the fact that both technologies have matured considerably, making this is a safe time to invest.

As we know, LCD screen is a negative display which can’t emit light on its own. It either relies on ambient light or uses LED backlight in the back as a light source. We divide LCD screen intotransmissive LCD, reflective LCD, and transflective LCDaccording to the employing mode of light. Also, we divide LCD screen into the positive display and negative display according to the light of the background part.

It is very simple, but most people can’t fully understand the meaning. We already introduced the difference between TN, HTN, STN and FSTN LCD in my previous post. The offset angle of liquid crystal in TN LCD is 90 degrees. What is that? If we see TN, HTN, STN and FSTN LCD in the perspective of view angle, it is much easier for us to understand.

Normally, it would be 6:00 o’clock direction or 12:00 o’clock direction. 6:00 o’clock direction means that we can see it clearly from the frontage and 6:00 o’clock direction. We can still see it clear from 3:00 or 9:00 o’clock direction if we make it well enough even it is 6:00 o’clock direction. The digital clock display in a car is installed on the right-hand side of the driver, which is usually 9:00 o’clock direction.

For example: if the view direction of TN LCD is 6:00 o’clock direction, you will see the graphic very blurred at any angle of 3:00 o’clock or 9:00 o’clock direction. We can still see it clearly within 20 degrees of 3:00 o’clock or 9:00 o’clock direction if it is 6:00 o’clock direction HTN LCD.

If you’re designing a display application or deciding what type of TV to get, you’ll probably have to choose between an OLED or LCD as your display type.

LCDs utilize liquid crystals that produce an image when light is passed through the display. OLED displays generate images by applying electricity to organic materials inside the display.OLED and LCD Main Difference:

graphics and images visible. This is the reason you’re still able to see light coming through on images that are meant to be dark on an LCD monitor, display, or television.

OLEDs by comparison, deliver a drastically higher contrast by dynamically managing their individual pixels. When an image on an OLED display uses the color black, the pixel shuts off completely and renders a much higher contrast than that of LCDs.OLED vs LCD - Who is better at contrast?

Having a high brightness level is important if your display is going to be used in direct sunlight or somewhere with high ambient brightness. The display"s brightness level isn"t as important if it’s going to be used indoors or in a low light setting.OLED vs LCD - Who is better at Brightness?

This means the display is much thinner than LCD displays and their pixels are much closer to the surface of the display, giving them an inherently wider viewing angle.

You’ll often notice images becoming distorted or losing their colors when tilting an LCD or when you view it from different angles. However, many LCDs now include technology to compensate for this – specifically In-Plane Switching (IPS).

LCDs with IPS are significantly brighter than standard LCDs and offer viewing angles that are on-par with OLEDs.OLED vs LCD - Who is better at Viewing Angles?

LCDs have been on the market much longer than OLEDs, so there is more data to support their longevity. On average LCDs have proven to perform for around 60,000 hours (2,500) days of operation.

With most LCDs you can expect about 7 years of consistent performance. Some dimming of the backlight has been observed but it is not significant to the quality of the display.

OLEDs are a newer technology in the display market, which makes them harder to fully review. Not only does OLED technology continue to improve at a rapid pace, but there also hasn’t been enough time to thoroughly observe their performance.

You must also consider OLED’s vulnerability to image burn-in. The organic material in these displays can leave a permanent afterimage on the display if a static image is displayed for too long.

So depending on how your OLED is used, this can greatly affect its lifespan. An OLED being used to show static images for long periods of time will not have the same longevity as one displaying dynamic, constantly moving images.OLED vs LCD - Which one last longer?

There is not yet a clear winner when it comes to lifespans between LCD and OLED displays. Each have their advantages depending on their use-cases. It’s a tie!

For a display application requiring the best colors, contrast, and viewing angles – especially for small and lightweight wearable devices – we would suggest an OLED display.

There are three main technologies used for projection – DLP, LCD and LED. DLP (Digital Light Processing) uses a chip made of tiny microscopic mirrors and a spinning colour wheel to create an image. DLP projectors deliver sharp images, don"t need any filters, have a better response time as well as 3D capabilities. The effective lamp life of a DLP projector is only 2000-5000 hours and some people see colour ghosting/banding in some scenes. On the other hand, LCD projectors use liquid crystal displays, have no moving parts and thus are generally less expensive. If you are on a budget a single chip LCD projector is ideal while 3-chip LCDs offer better colour saturation, lower noise levels and work better for movies. However, LCDs require constant filter maintenance and output less contrast. The LEDs in LED projectors have a lifespan of over 20,000 hours. They deliver better colours, have lower power consumption and virtually zero maintenance costs. Also, LED projectors are smaller and generate less heat. Do keep in mind that LED projectors have limited brightness compared to LCD or DLP so they are not recommended if your room has a lot of ambient light.

Tip: Some high-end projectors come with a feature called lens-shift. This is a physical rail that adjusts the lens up/down & sideways to move the image around. Obviously, this offers a lot more flexibility with regards to projector placement.

Pico projectors use LEDs as the light source due to which they can be extremely compact in size. Pico projectors can fit in your palm or be integrated into various devices like mobile phones (Samsung Galaxy Beam), tablets (Lenovo Yoga Tab 3), computers, and even digital cameras (Nikon S1000pj). While these projectors do not offer very high resolution or brightness, they are good enough to use in a small, dark room. You can get a 60-inch screen and you can connect multiple devices like smartphones, gaming consoles and laptops. Moreover, the portable size enables manufacturers to add internal storage as well as rechargeable battery in devices that weight less than 200 grams.

Some movies are shot in widescreen (16:9 or wider) – but to display them in standard width video formats (4:3 or square), you will see black bars above and below the display area. This is called letterboxing

A 3 colour LCD system uses individual LCDs for red, green and blue. The light from each LCD is combined using a prism to create a final image. It usually offers better quality than single chip LCD or DLP designs.

There’s been a significant growth in the monitor market when it comes to screens with LED backlighting. I wanted to provide an article which explains the technology in more detail as it is bound to become more and more widespread. The technology was originally quite expensive, but reduced production costs and improved manufacturing processes have allowed LED backlighting to be used in even the lower cost monitor market. We are now seeing an influx of new screens in all different sizes using LED backlighting, and it is also being combined with TN Film, VA and IPS panel technologies.

RGB LED Backlighting – This type of backlighting is based on RGB triads, each including one red, one green and one blue LED. RGB LED backlighting ensures an excellent colour gamut and very pure colours, but is only really used in professional-grade displays such as the Samsung XL20, XL24, XL30 screens, and modern professional models like the HP DreamColor LP2480zx. This type of backlighting is only used in this sector due to its high cost and it is not economical to produce at the moment.

An edge backlight with white LEDs (W-LEDs) –The LEDs are placed in a line along the edge of the matrix, and the uniform brightness of the screen is ensured by a special design of the diffuser. This backlight does not offer the option of zonal control over brightness like the direct lit method does (see below). It can not offer an extended color gamut either. Instead, it is economical and compact, which makes it popular among notebook makers and with manufacturers producing ultra-thin displays and keen to keep costs to a minimum. This is the variation commonly being used in desktop displays at the moment.

A flat backlight based on white LEDs (W-LEDs) – As there is only one third of the total amount of LEDs here, this backlight is much cheaper than the triad-based backlight, but it cannot deliver an extended color gamut. In the backlight of this type LEDs are uniformly distributed in the plane parallel to the matrix, which allows setting the backlight intensity differently in different parts of the screen when necessary. This is the further development of the dynamic contrast technology. It is currently employed in LCD TV-sets only and is also referred to as ‘direct lit’ W-LED. A note about white LEDs – A white LED is actually a blue LED with yellow phosphor to give the impression of white light. The spectral curve has big gaps in the green and red parts.

If marketing is to be believed, LED backlighting offers you all kinds of advantages, but it’s important to understand what is true, and what is not. We will discuss different aspects and whether they are influenced by a different backlight source:

Colour Gamut– this is controlled in monitors by the properties of the colour filters of the LCD matrix, and by the backlight’s radiation spectrum. You will see CCFL backlighting offering colour gamuts covering between 72% (commonly referred to as “standard gamut” / sRGB) and 102% of the NTSC reference colour space. The CCFL backlighting above 72% are commonly referred to as wide gamut, or W-CCFL / WCG-CCFL. In LED backlighting, the RGB LED format can offer really large colour gamuts with pure and saturated colours. These can cover typically >114% of the NTSC colour space, and is one of the reasons they are often employed in high end professional screens. W-LED backlighting cannot offer these extended gamuts, and on paper actually cover slightly less of the NTSC colour space than standard gamut CCFL (typically 68%). The difference is hardly detectable by the naked eye however.

Static contrast ratio – LED backlighting models are advertised with massive contrast ratios, ranging commonly into the millions now! Figures of up to 20 million:1 are common at the time of writing. Be aware though that these are normally headline dynamic contrast ratio figures, with the normal static contrast ratio rarely even mentioned. It is important to understand that static contrast ratio is only determined by the characteristics of the LCD matrix itself and not by the backlighting type or nature. It is determined by the ratio of the transparency levels of open and closed pixels.

Dynamic contrast ratio – As opposed to gas-discharge lamps (CCFL), LEDs can be lit up instantly or turned out completely. This can lead to extremely high levels of dynamic contrast as we have mentioned above. Figures in the millions are very common now. But in real applications, for example when watching a movie, there are no absolutely black frames even in the credits. Most of the time there is something on the screen besides blackness and a monitor with a huge specified dynamic contrast will never have the chance to deliver it in practice. As a result, there is no real practical point in increasing the dynamic contrast higher than about 10,000:1 which has already become standard for many monitors, including those with a backlight based on CCFL lamps. Keep in mind that DCR figures are often exagerated as a result, and since you will probably never get to utlise the full figure in practice, don’t be fooled into buying into the hype too much!

Uniformity – Most desktop monitors use edge-lit W-LED backlighting with a line of LEDs along the edge of the panel. The whole screen is lit by means of a special diffuser, and so it is this which really determines the brightness uniformity you experience. The uniformity of brightness depends only on the design of the diffuser and you can often see various defects like bright spots or a brighter zone at the edge of the screen where the lamp or the line of LEDs resides. Having an LED backlight does not guarantee you better uniformity. In fact, good uniformity is harder to achieve in the long term as the LEDs age, with each LED possibly aging at a different rate. With RGB LED units, the use of three separate light sources for red, green, and blue means that the white point / colour temperature of the display can move as the LEDs age at different rates as well.

Instantly On – some manufacturers mention that an LED can be instantly turned on, meaning there is no warm up time like there is with a CCFL backlight. This is true, but it’s debatable how important this really is to an end user.

Size – LED backlighting units can be very thin, allowing manufacturers to produce ultra-thin displays with sleek and attractive designs. You also see this technology used in laptops and LCD TV’s for the same purposes. This technology has allowed production of thinner screens which are in high demand by consumers. Manufacturers are actively working on reducing the size of the LEDs to be used in these modules to improve things even more. Screens using a flat W-LED or RGB backlight behind the panel cannot offer the same thin profile however.

Environmental – LEDs do not contain mercury, unlike CCFL’s and so can be recycled more easily. You will see mention of various certificates and compliance standards as well, such as ‘RoHS compliance’. These can show the displays have met recylcing standards. Certainly a benefit of LED backlighting for the environmentally concious.

Power Consumption– This is perhaps one of the key advantages of LED backlighting in modern times. The technology uses less energy and so you can save money and energy and reduce your carbon footprint at the same time. For example, the non-LED version of the 24″ BenQ G2420HBD consumer display has a 49W consumption compared to the 24W of the LED version of the same display (G2420HBDL). The BenQ LED monitors are typically marketed as offering a reduced power consumption of 36% in comparison to traditional monitors. Other manufacturers quote similar figures, with 35 – 40% energy saving being common. You will also see various ratings and ‘certificates’ applied to these screens such as Energy Star and the likes.

At the professional end of the market where RGB LED backlighting is used, it is combined with high end panel technologies such as AMVA (from AU Optronics) or IPS (from LG.Display). These panel technologies are more expensive to produce than the widely used TN Film panels in the mainstream market. When you are using an expensive backlighting unit, it obviously should be paired with a higher-end panel though. In fact, modern RGB LED displays such as the HP DreamColor LP2480zx even use a one-of-a-kind true 10-bit H-IPS panel (not 8-bit +AFRC like some of the other modern “10-bit” screens). RGB LED models are few and far between though of course.

W-LED backlit models are becoming more and more mainstrea. Initially the technology was combined exclusively with TN Film panels, since low production costs (and low retail costs) were the name of the game. There are many TN Film based models out there with LED backlighting now. More recently, in the later half of 2010, we have seen models emerge combining W-LED backlighting with VA and IPS matrices. AU Optronics have released modules in several sizes which combine their AMVA panel technology with LED, and LG.Display have begun to release a combination of IPS and LED. The BenQ EW2420 and VW2420H were two of the first VA based screens on the market with LED. The NEC EA232WMi and forthcoming models from LG will be some of the first to use IPS + LED. We expect this trend will continue.

LCD stands for “Liquid Crystal Display” and TFT stands for “Thin Film Transistor”. These two terms are used commonly in the industry but refer to the same technology and are really interchangeable when talking about certain technology screens. The TFT terminology is often used more when describing desktop displays, whereas LCD is more commonly used when describing TV sets. Don’t be confused by the different names as ultimately they are one and the same. You may also see reference to “LED displays” but the term is used incorrectly in many cases. The LED name refers only to the backlight technology used, which ultimately still sits behind an liquid crystal panel (LCD/TFT).

As TFT screens are measured differently to older CRT monitors, the quoted screen size is actually the full viewable size of the screen. This is measured diagonally from corner to corner. TFT displays are available in a wide range of sizes and aspect ratios now. More information about the common sizes of TFT screens available can be seen in our section about resolution.

The aspect ratio of a TFT describes the ratio of the image in terms of its size. The aspect ratio can be determined by considering the ratio between horizontal and vertical resolution.

The resolution of a TFT is an important thing to consider. All TFT’s have a certain number of pixels making up their liquid crystal matrix, and so each TFT has a “native resolution” which matches this number. It is always advisable to run the TFT at its native resolution as this is what it is designed to run at and the image does not need to be stretched or interpolated across the pixels. This helps keep the image at its most clear and at optimum sharpness. Some screens are better than others at running below the native resolution and interpolating the image which can sometimes be useful in games.

You generally cannot run a TFT at a resolution of above its native resolution although some screens have started to offer “Virtual” resolutions, for example “virtual 4k” where the screen will accept a 3840 x 2160 input from your graphics card but scale it back to match the native resolution of the panel which is often 2560 x 1440 in these examples. This whole process is rather pointless though as you lose a massive amount of image quality in doing so.

Ultra-high resolutions must be thought of in a slightly different way. Ultra HD (3840 x 2160) and 4K (4096 x 2160) resolutions are being provided nowadays on standard screen sizes like 24 – 27” for instance. Traditionally as you increased the resolution of panels it was about providing more desktop real estate to work with. However, with those resolutions being so high, and the screen size being relatively small still, the image and text becomes incredibly small if you run the screen at normal scaling at those native resolutions. For instance imagine a 3840 x 2160 resolution on a 24” screen compared with 1920 x 1080. The latter would probably be considered a comfortable font size for most users. These ultra-high resolutions nowadays are about improving image clarity and sharpness, and providing a higher pixel density (measured as pixels per inch = PPI). In doing so, you can improve the sharpness and clarity of an image much like Apple have famously done with their “Retina” displays on iPads and iPhones. To avoid complications with tiny images and fonts, you will then need to enable scaling in your operating system to make everything easier to see. For instance if you enabled scaling at 150% on a 3840 x 2160 resolution, you would end up with a screen real estate equivalent to a 2560 x 1440 panel (3840 / 1.5 = 2560 and 2160 / 1.5 = 1440). This makes text much easier to read and the whole image a more comfortable size, but you then get additional benefits from the higher pixel density instead, which results in a sharper and crisper image.

Generally you will need to take scaling in to consideration when purchasing any ultra-high resolution screen, unless it’s of a very large size. The scaling ability does vary however between different operating systems so be careful. Apple OS and modern Windows (8 and 10) are generally very good at handling scaling for ultra-high res displays. Older operating systems are less capable and may sometimes be complicated. You will also find varying support from different applications and games, and often end up with weird sized fonts or sections that are not scaled up and remain extremely small. A “standard” resolution where you don’t need to worry about scaling might be simpler for most users.

To display this content of this type, your screen needs to be able to 1) handle the full resolution naturally within its native resolution, and 2) be able to handle either the progressive scan or interlaced signal over whatever video interface you are using. If the screen cannot support the full resolution, the image can still be shown but it will be scaled down by the hardware and you won’t be take full advantage of the high resolution content. So for a monitor, if you want to watch 1080 HD content you will need a monitor which can support at least a vertical resolution of 1080 pixels, e.g. a 1920 x 1080 monitor.

Unlike on CRT’s where the dot pitch is related to the sharpness of the image, the pixel pitch of a TFT is related to the distance between pixels. This value is fixed and is determined by the size of the screen and the native resolution (number of pixels) offered by the panel. Pixel pitch is normally listed in the manufacturers specification. Generally you need to consider that the ‘tighter’ the pixel pitch, the smaller the text will be, and potentially the sharper the image will be. To be honest, monitors are normally produced with a sensible resolution for their size and so even the largest pixel pitches return a sharp images and a reasonable text size. Some people do still prefer the larger-resolution-crammed-into-smaller-screen option though, giving a smaller pixel pitch and smaller text. It’s down to choice and ultimately eye-sight.

Of course the problem with this is that if you run a screen as small as 27″ with a 5K resolution, the font size is absolutely tiny by default. You get a massive boost of desktop real-estate, just like when moving from 1920 x 1080 to 2560 x 1440, but that’s not the purpose of these higher resolutions now. To overcome this you need to use the scaling options in your Operating System software to scale the image and make it more usable. Windows provides for instance scaling options like 125% and 150% within the control panel. On a 3840 x 2160 Ultra HD resolution if you use a 150% scaling option for example you will in effect reduce the desktop area by a third, resulting in the same desktop area as a 2560 x 1440 display (i.e. 2560 x 150% = 3840). The OS scaling makes font sizes more comfortable and reasonable, but you maintain the sharp picture quality and small pixel pitch of the higher resolution panel. A 3840 x 2160 res panel scaled at 150% in Windows will look sharper and crisper than a 2560 x 1440 native panel without scaling, despite the fact both would have the same effective desktop area available.

While this aspect is not always discussed by display manufacturers it is a very important area to consider when selecting a TFT monitor. The LCD panels producing the image are manufactured by many different panel vendors and most importantly, the technology of those panels varies. Different panel technologies will offer different performance characteristics which you need to be aware of. Their implementation is dependent on the panel size mostly as they vary in production costs and in target markets. The four main types of panel technology used in the desktop monitor market are:

IPS was originally introduced to try and improve on some of the drawbacks of TN Film. While initially viewing angles were improved, the panel technology was traditionally fairly poor when it came to response times and contrast ratios. Production costs were eventually reduced and the main investor in this technology has been LG.Display (formerly LG.Philips). The original IPS panels were developed into the so-called Super IPS (S-IPS) generation and started to be more widely used in mainstream displays. These were characterized by their good colour reproduction qualities, 8-bit colour depth (without the need for Frame Rate Control) and very wide viewing angles. These panels were traditionally still quite slow when it came to pixel response times however and contrast ratios were mediocre. In more recent years a change was made to the pixel alignment in these IPS panels (see our detailed panel technology article for more information) which gave rise to the so-called Horizontal-IPS (H-IPS) classification. With the introduction of overdrive technologies, response times were improved significantly, finally making IPS a viable choice for gaming. This has resulted more recently in IPS panels being often regarded as the best all-round technology and a popular choice for display manufacturers in today’s market. Improvements in energy consumption and reduced production costs lead to the generation of so-called e-IPS panels. Unlike normal 8-bit S-IPS and H-IPS classification panels, the e-IPS generation worked with a 6-bit + FRC colour depth. Developments and improvements with colour depths also gave rise to a generation of “10-bit” panels with some manufacturers inventing new names for the panels they were using, including the co-called Performance-IPS (p-IPS). It is important to understand that these different variants are ultimately very similar and the names are often interchanged by different display vendors. For more information, see our detailed panel technologies guide.

Nowadays IPS panels are produced and developed by several leading panel manufacturers. LG.Display technically own the IPS name and continue to invest in this popular technology. Samsung began production of their very similar PLS (Plane to Line Switching) technology, as did AU Optronics with their AHVA (Advanced Hyper Viewing Angle). These are all so similar in performance and features that they can be simply referred to now as “IPS-type”. Indeed monitor manufacturers will normally stick to the common IPS name but the underlying panel may be produced by any number of different manufacturers investing in this type of panel tech. AU Optronics have done a good job with finally increasing the refresh rate of their IPS panels, and making them a more viable option for gamers. Native 144Hz IPS-type panels are now available and response times continue to be reduced as well. Modern IPS panels are characterized by decent response times, if not quite as fast as TN Film they are certainly more fluid than older panels. Contrast ratios are typically around 1000:1 and viewing angles continue to be the widest and most stable of any panel technology. You will find varying colour depths including 6-bit+FRC and 8-bit commonly being used, although this makes little difference in practice. One of the remaining limitations with IPS-type technologies are the so-called “IPS glow”, where darker content introduces a pale glow when viewed from an angle. It’s a characteristic of the panel technology and pretty hard to avoid without additional filters being added to the panels. On larger and wider screens some people find this glow distracting and problematic.

The original early VA panels were quickly scrapped due to their poor viewing angles, and in their place came the two main types of VA matrix. Multi-Domain Vertical Alignment (MVA) and Patterned Vertical Alignment (PVA) panels. These VA variants were characterized by their reasonably wide viewing angles, being better than TN Film but not as wide as IPS. They were originally poor when it came to pixel response times but offered 8-bit colour depths and the best static contrast ratios of all the technologies discussed here. Traditionally VA panels were capable of static contrast ratios of around 1000 – 1200:1 but this has even been improved now to 3000:1 and above. Until very recently VA panels remained very slow and so were not really suitable for gaming. However during 2012 we saw advancements with the latest generation of VA panels and through the use of overdrive technologies this has been significantly improved. Perhaps the main limitation with VA panels is still their viewing angles when compared with popular IPS panel options. Gamma and contrast shifts can be an issue and the technology also suffers from an inherent off-centre contrast shift issue which can be distracting to some users. Through the years we have seen several different generations of VA panels. AU Optronics are the main manufacturer of MVA matrices, and we have seen the so-called Premium-MVA (P-MVA) and Advanced-MVA (AMVA) generations emerge. Chi Mei Innolux (previously Chi Mei Optoelectronics / CMO) also make their own variant of MVA which they call Super-MVA (S-MVA).The only manufacturer of PVA panels is Samsung as it is their own version of VA technology. We have seen several generations from them including Super-PVA (S-PVA) and cPVAandSVA. For more information, see our detailed panel technologies guide.

This technology was developed by Sharp for use in some of their TFT displays. It consists of several improvements that Sharp claim to have made, mainly to counter the drawbacks of the popular TN Film technology. They have introduced an Anti-Glare / Anti-Reflection (AGAR) screen coating which forms a quarter-wavelength filter. Incident light is reflected back from front and rear surfaces 180° out of phase, thus canceling reflection rather diffusing it as others do. As well as reducing glare and reflection from the screen, this is marketed as being able to offer deeper black levels. Sharp also claim to offer better contrast ratios than any competing technology (VA and IPS); but with more emphasis on improving these other technologies, this is probably not the case with more modern panels. There are very few ASV monitors around really, with the majority of the market being dominated by TN, VA and IPS panels.

This technology was developed by BOE Hydis, and is not really very widely used in the desktop TFT market, more in the mobile and tablet sectors. It is worth mentioning however in case you come across displays using this technology. It was developed by BOE Hydis to offer improved brightness and viewing angles to their display panels and claims to be able to offer a full 180/180 viewing angle field as well as improved colours. This is basically just an advancements from IPS and is still based on In Plane technology. They claim to “modify pixels” to improve response times and viewing angles thanks to improved alignment. They have also optimised the use of the electrode surface (fringe field effect), removed shadowed areas between pixels, horizontally aligned electric fields and replaced metal electrodes with transparent ones. More information about AFFS can be found here.

This panel technology was developed by NEC LCD, and is reported to offer wide viewing angles, fast response times, high luminance, wide colour gamut and high definition resolutions. Of course, there is a lot of marketing speak in there, and the technology is not widely employed in the mainstream monitor market. Wide viewing angles are possible thanks to the horizontal alignment of liquid crystals when electrically charged. This alignment also helps keep response times low, particularly in grey to grey transitions. Their SFT range also offers high definition resolutions and are commonly used in medical displays where extra fine detail is required.

NEC’s SFT technology was first developed to be labelled as Advanced-SFT (A-SFT) which offered enhanced luminance figures. This then developed further to Super Advanced-SFT (SA-SFT) where colour gamut reached 72% of the NTSC colour space, and then to Ultra Advanced-SFT (UA-SFT) where the gamut was still at 72% or higher, but with a further enhancement of the luminance as compared with SA-SFT. These changes were all made possible thanks to the improved transmissivity of the SFT technology. More information is available from NEC LCD

One thing to note regarding pixel response time is that the overall performance of the TFT will also depend on the technology of the panel used. TN film panels offer response time graphs similar to that above, but screens based on traditional VA / IPSvariant panels can show response time graphs more like this (we are assuming for now non-overdriven panels):

Some reviews sites including TFTCentral have access to advanced photosensor (photodiodе + low-noise operational amplifier) and oscilloscope measurement equipment which allows them to measure response time as detailed above. See our article about response times for more information on that method. Graphs showing response time according to their equipment are produced. Other sites rely on observed responsiveness to compare how well a panel can perform in practice and what a user might see in normal use. We think it is important to study both methods if possible to give a fuller picture of a panels performance. For visual tests TFTCentral uses a program called PixPerAn (developed by Prad.de) which is good for comparing monitor responsiveness with its series of tests. The favourite seems to be the moving car test as shown here:

Movement isn’t perfectly fluid. Depending on its speed, the car is shown in several successive positions. If the car goes very fast, the positions are very close and the eye perceives a flowing movement. A monitor without ghosting effects would have previous images completely fading away when a new one appears. This is the theory and in practice, it’s often not the case as images fade progressively. Sometimes up to 5 afterglow images remain on the monitor and represent the visible white trail behind objects. Some monitors have strong overdrives in addition to image anticipation algorithms and where these are too aggressively applied, or poorly controlled, it can result in problems. In this case, an image can appear in front or behind the main object, creating a white or dark halo commonly.

In addition to pixel response time measurements and visual tests described above, it is also possible to capture the levels of blurring and smearing the human eye will experience on a display. This is achieved using a pursuit camera setup. They are simply cameras which follow the on-screen motion and are extremely accurate at measuring motion blur, ghosting and overdrive artefacts of moving images. Since they simulate the eye tracking motion of moving eyes, they can be useful in giving an idea of how a moving image appears to the end user. It is the