Understanding Different Display Types: OLED, LCD, QLED, and More

Technological advancements have led to the development of various kinds of devices. A key feature of these devices is the display. It acts as the primary interface used to interact with the device. These displays are as many as the categories of displays. In this article, you will learn the technologies, features, and use cases of the various types of displays.

LED displays

Technological advancements have led to the development of various kinds of devices. A key feature of these devices is the display. It acts as the primary interface used to interact with the device. These displays are as many as the categories of displays. In this article, you will learn the technologies, features, and use cases of the various types of displays.

Light Emitting Diodes (LEDs) are the building blocks of LED display technology. These diodes are small semiconductors that emit light when electric current is passed through them. LED displays are quite common for their superior features.

How LED displays work

To understand how LED displays work, you need a basic understanding of LEDs. Also, since LED displays have an LCD layer, we will explore how the two work together.

The mechanism of how LEDs work is interesting. The whole mechanism is based on a process known as electroluminescence. Essentially, electroluminescence is the emission of light when electrons flow to a substrate. In other words, electric energy is converted to light without the production of heat. This is one of the reasons why LED displays are known to not have high heat emission.

LED chips are made using Red, Blue, and Green semiconductor materials. These are also known as primary colors, in relation to color depth. Using specialized algorithms and hardware, LED displays mix these primary colors to produce a wide range of colors. LED displays can reproduce up to 16 million colors from red, green, and blue.

LED displays have an LCD layer. The LED lights are used for backlighting that shines light needed to create an image on the LCD panel. Put simply, an LED display is a special type of LCD. They are also referred to as LED-backlit LCD displays.

Liquid crystal displays (LCDs) are made of liquid crystals sandwiched between glass or plastic panels. These crystals respond to changes in electric current and light. The technical term for this process is polarization of light. 

The light from LED lights controls the passage or blockage of light to the LCD panel. This facilitates the formation of images on the screen. Color filtering is applied to full-color LED displays for more accurate and precise color reproduction. This is the basic process of how LED displays work.

Characteristics of LED displays 

The inner workings of LED displays reveal so much about the characteristics of this display technology. Characteristics are essentially the defining features of this technology. Some of the most noticeable characteristics include;

  • LED lights produce directional light. Emitting light in one direction is one of the reasons for the high lighting efficiency experienced. In other words, there is reduced energy waste from the display.
  • Sensitive to temperature increase. LEDs are negatively affected by an increase in temperature during the electron flow process. If the temperature rises beyond a certain threshold, the lumen efficacy of the LED is affected.
  • LEDs require low energy. The power needed to light up the LED crystals is minimal due to the direct contact of the electrons and the conductive regions of the LED crystal. This is why LED displays are so energy-efficient.
  • They have a long lifespan. A lifespan is the time it takes before the LED lumen efficacy depreciates completely. LED displays can function optimally for 10 years with the right maintenance.

Types of LED displays

There are two major types of LED displays. These can also be considered categories from which every LED display is based. They are;

Direct-lit LED

In these types of LED displays, the LED backlighting diodes are placed on the back of the main panel. The encapsulation method used to pack these semiconductors will depend on the device and the manufacturing standards applied.

Direct-lit LEDs have a local dimming feature which ensures that the display can have a better contrast. This happens with the help of individual pixel lighting and other technologies. Most devices use direct-lit LED displays.

Edge-lit LED

As the name implies, these displays have LED chips placed on the edges of the display. They are mostly along the top or the bottom sides of the panel. Since LEDs are used for backlighting, this placement works. The LCD panel is what’s responsible for producing images.

One problem with edge-lit LED displays is the lack of local dimming. Therefore, the screen is unable to achieve better contrast levels. This can cause issues of uniform brightness, especially for vivid images in the dark. However, devices that have edge-lit displays are slim because of the lack of a separate panel for housing the LED chips.

Organic Light-Emitting Diode (OLED) displays

While LED displays have an LCD panel and a backlighting mechanism, the light from OLED displays is emitted directly from the pixels that are made up of LED semiconductors. In other words, OLED displays have are self-illiminating LED pixels. Let us learn how this works.

How OLEDs works

OLED in full is an organic light-emitting diode. The name organic implies that the semiconductor material that makes OLED chips is organic. Specifically, the OLED pixels have what is known as the emissive layer that is responsible for light reproduction.

Light has varying wavelengths. These wavelengths are responsible for the different colors that we encounter. Like LED displays, OLEDs are also based on the electroluminescence principle. The main difference is that there is no LCD panel in OLED displays. 

An OLED has another layer known as the conductive layer. This layer aids in the transport of electrons to the emissive layer. The physics of this process is not relevant in this article. What you should keep in mind is that the OLED display has primarily three layers that function concurrently to produce an image on the device.

Learning the characteristics of this display technology will help you get a deeper understanding of how everything works.

Characteristics of OLEDs

If you have watched content from an OLED TV, you can attest to the brightness, vividness, contrast, and color depth of the display. This happens because of the special features of the OLED technology. Some of the characteristics that define OLED displays include;

  • OLEDs have high contrast levels. Contrast is facilitated by many factors. The common reason is the individual switching of pixels. Imagine local dimming but at an advanced level. Also, OLED chips have a high response time, which ensures a fast switching between colors. 
  • OLED displays have wide viewing angles. This means content can be viewed at extreme angles and still appear correct. Due to the minute nature of OLED pixels, displays tend to have high resolution, which promotes the sharpness and clarity of images.
  • OLED displays have burn-in effects. This is a negative characteristic of OLEDs that is worth mentioning. It is an image retention that occurs on the screen and can be permanent or temporary. It is caused by pixel aging, overuse, and other factors. This is common but it can be avoided or controlled depending on its severity.
  • Vivid color reproduction. The lack of a backlighting mechanism and an LCD panel gives OLED displays an edge in color reproduction. The pixels independently produce color and turn on and off depending on the need. This achieves something called “true black” levels of color. This supports vivid and true color reproduction.

Types of OLED displays

OLED displays are classified based on pixel arrangement and addressing. This classification gives us PMOLED and AMOLED displays. Let us discuss the two in more detail.

AMOLED

Active matrix OLED (AMOLED) is a type of OLED display technology that uses a thin film transistor (TFT) to control each individual pixel. In particular, the TFTs control the flow of current to the pixels, thereby acting as a switch for the pixel addressing. It helps control the brightness and response rates of the pixels.

The scheme of having individual TFTs controlling individual pixels is what defines the “active matrix” addressing. It has several advantages over its counterpart — PMOLED.

The TFTs in AMOLED technology are quite essential in this technology. They are responsible for the high refresh rates and response times. Controlling and fine-tuning an AMOLED display is quite flexible due to these TFTs. The same would not be said about PMOLEDs.

PMOLED

This type of OLED display has a different scheme for pixel addressing. The PM in the acronym stands for passive matrix. It implies that the pixels are arranged in a matrix pattern. In PMOLED, the passive matrix addressing is used to control the pixels.

Unlike in AMOLED where pixels are addressed individually, pixels in PMOLED displays are addressed in rows and columns. This does not happen all at once as is the case with AMOLED displays. Therefore, it ensures that the screen lights up where it needs to according to the pixels in the activated column or row.

PMOLED displays have low resolution and brightness due to the addressing scheme used. Still, there are many devices that utilize this technology, particularly for its approach to pixel control and addressing. They include wearables like smartwatches and medical device screens.

LCD displays

This is another popular but classical type of display. It is among the display technologies that were used in the revolution of devices. LCD displays should not be mistaken for LED-backlit LCD displays since they are quite different.

How LCD displays work

LCD displays are made of a special liquid trapped between glass or plastic panels. The enclosure substrate is transparent to allow the passage of light. Since light can be directed in any direction, the liquid crystals in the LCD panel are there to control the direction of light it receives. This light comes from a lamp or another light source. 

These types of displays have an on-and-off state. The on-state means that electric current is passing through the pixels. With the help of the alignment layer, the liquid crystals align with the electric field allowing the pixel to light up. In the off-state, there is no alignment or activation of the pixels, hence they remain turned off.

Characteristics of LCDs

There are many characteristics that define LCD displays. 

  • LCD displays require backlighting. An LCD panel cannot function without a light source to illuminate the main display. These backlights are either on the back or on the edges of the panel enclosure. 
  • LCDs are not energy-efficient. The backlighting of LCDs requires a lot of power to achieve high brightness. This is true, especially in cases where the source of light is an outdated technology like fluorescent bulbs.

LCD displays might be considered poor when compared to more recent and modern display technologies. However, it outperforms its predecessors such as CRT displays.

Types of LCD displays 

There are four main types of LCD displays. Each has its own mechanism. The four are essentially distinguished by the alignment of liquid crystals during on and off states. Let us look at them closely at these four types. 

Twisted nematic (TN) LCDs

In this type of LCD, the liquid crystals align in a twisted form factor when there is no electric current flowing to the layer. This renders the display opaque since no light passes through. When power is turned on, they untwist themselves to allow the flow of light to the LCD panel. Twisted nematic LCDs are some of the oldest types of LCD displays.

Vertical alignment (VA) LCDs

As the name implies, the sandwiched liquid crystals are aligned vertically during the off state. This stops the passage of light from the backlight. They change to a horizontal orientation when electric current flows through. 

VA-LCDs are known to have high contrast ratios but they have a subpar response rate and a narrow viewing angle. 

In-plane switching (IPS) LCDs

In this type of LCD, the liquid crystal cells are aligned horizontally when they are not electrically powered. This allows them to have a wide-angle to switch and open up when electrons flow through the cells. It is also the reason why it’s called an in-plane switching. The cells rotate to a 90-degree angle when lit up to allow light passage.

Thin-film transistor (TFT) LCDs 

TFT LCDs are the most common kinds of LCD displays. Remember the addressing scheme used in AMOLED displays? Well this type of LCD uses a similar approach to control individual pixels. The only difference is that in this case, it is the liquid crystals being controlled by the transistors.

These types of LCDs have a high resolution and color accuracy. Also, the TFTs improve the response time of the display pixels. In return, this contributes to a fast, and efficient display for everyday gadgets.

Quantum Dot LED (QLED) displays

Display technologies are always looking for ways to make pixels smaller. Quantum dot technology is one of the progressive frontiers in this race. QLED displays use quantum dot semiconductors as the light-emitting chips. The term quantum represents their minute size and also their properties.

How QLEDs works

QLED display technology was developed by Samsung but it has been used across the industry by various manufacturers. It is a type of LED-backlit LCD technology that uses tiny nanoparticle semiconductor materials as the backlight source.

Nanoparticles have a diameter of between 1 and 100 nanometers. For reference, the human hair is about 50 micrometers. That means it is a quantum dot — nanoparticle — that is thousands of times smaller than one strand of human hair. This small size gives the quantum dots many benefits over other semiconductors.

The quantum dots in the QLED display create a color filter layer. This layer enhances color correctness and improves the brightness of the display. For backlight, QLEDs use a separate set of blue LED chips for backlighting. 

Image reproduction on a QLED display is a little different from other LCD displays. These displays use an enhancement technique where the LEDs shed light through a layer containing quantum dot nanoparticles. This light is usually white but the quantum dots convert it into the primary colors before sending it into the LCD panel.

Characteristics of QLEDs

Quantum dot technology is known for its superior features due to the dedicated engineering that goes into producing the QLED layer. Some of the characteristics of this display technology include the following;

  • The quantum dots are inorganic. Inorganic materials are durable and not susceptible to rapid degradation. This means QLED displays can maintain high color accuracy for extended periods.
  • No burn-in effects. We saw earlier that OLED displays are likely to experience burn-in effects for several reasons. QLED displays do not experience this problem. This makes them a superior choice of display.
  • HDR capabilities. High dynamic range is the ability of a display to have a range of dark and light tones in an image. QLED is among the few display technologies that can achieve this level of contrast ratio in images. HDR improves the clarity and accuracy of content.
  • Adaptability. This is defined as the ability to adapt features to improve the overall experience of the display. Local dimming and adaptive brightness are among the adaptability features of QLED displays.

Micro-LED displays

These types of displays have been dubbed ‘the future of display technology’. They are essentially microscopic LED semiconductor chips. In other words, they are so tiny that they can only be seen with the aid of a microscope.

Micro LED chips are grown in a lab using a procedure known as epitaxy. This technique, which can happen in different ways, facilitates the formation of thin crystalline films of atoms under specific conditions. The nanoparticles are then transferred from the wafers to the substrate material forming the emission layer in the display panel.

How Micro-LED displays works 

The mechanism of micro-LED displays is similar to that of OLEDs. Electroluminescence powers up the micro LED chips thereby emitting color depending on the wavelength of the light. However, it is not as easy as it sounds.

In OLED displays, one pixel is made of three (red, green, and blue) LED chips. When we get to the micro level, the number of chips found in pixels increases. However, you will still find micro-LED displays that have one LED chip per subpixel. Micro LED displays that have multiple LEDs per subpixel are brighter. 

Micro LED displays have a backplane layer that houses the TFTs required to control the pixel brightness. This is one of the reasons micro LED displays have a full array of local dimming capabilities.

These displays use a color mixing technology to mix the primary colors and reproduce a wide range of colors. Individual pixel control is essential in the reproduction of colors. It promotes better contrast, luminance, brightness, and color accuracy.

Characteristics of Micro-LEDs

This display technology has several features such as;

  • High pixel density. Shrinking down the size of the pixels to minute levels allows manufacturers to create high-pixel-density displays.
  • Expensive to manufacture. Epitaxy is an expensive process, especially in large-scale production. This makes the overall manufacture of micro LEDs quite expensive. For this reason, micro LED displays are made for smaller devices like VR and AR headsets. Still, large devices such as video walls can be made using micro LED technology.
  • Superior quality display. Every feature of a display that you can think about is superior in micro-LED displays. Whether it is screen brightness, power efficiency, color gamut — you name them. 

Mini-LED displays

This type of display can be considered the middle child. Its size is neither too big like regular LEDs but also not as small as micro LEDs. Reducing the size of LEDs has many advantages as we have seen with micro LEDs.

How Mini-LEDs works

This is one of the newest display technologies that is making a great impression on buyers and makers alike. Like regular LED screens, mini-LED is primarily a backlighting for LCD displays. Most display manufacturers have made diverse devices using this technology.

The goal of mini-LED over regular LED backlighting is to improve brightness levels, color accuracy, performance, and pixel density of the panel. mini-LEDs are not just about reducing their size. They have been equipped with more advanced features.

One of the major features of mini-LED displays is Shape Adaptive Light Control. This is a feature that allows the display to automatically adjust its brightness. The mini-LED semiconductor system is equipped with a light sensor mechanism that aids with this capability.

The mini-LED technology will eventually revolutionize many aspects of display technologies in the years to come.

Characteristics of Mini-LEDs

Factoring in the rapid advancements happening with display, we can say that mini-LEDs are right at the top. The goal has always been to make the ultimate display that represents the true nature of the world as we perceive it. Some of the characteristic features of mini-LEDs support this assertion. They include;

  • Intelligent features. The Internet of Things (IoT) is a feature that is being pushed for many devices as the world aims to achieve total interconnectivity. Therefore, with displays being at the forefront of this revolution, it makes sense for them to have certain intelligent features. Shape Adaptive Light Control is a great example. 
  • Better than regular LED. We have seen that mini-LEDs are way more advanced than regular LEDs in multiple ways. When it comes to local dimming, pixel control, enhancement, and overall control, mini-LEDs are much more capable.
  • Blooming effect from local dimming. In an attempt to achieve true blacks, LCD displays with mini-LED backlighting have a blooming effect on the display. This means that the effort to increase the contrast between dark and light levels leads to a light-spilling effect on the dark parts of the display. It is a disadvantage and can result in poor contrast ratios.

Plasma displays

Although most manufacturers discontinued the manufacture of these displays, they are worth mentioning in this article. 

Plasma is a fundamental state of matter. It is a conductive medium that has negative and positive electrodes. Therefore, it responds to electron energy. Plasma displays were used in flat panel devices. This technology was considered more capable than the options that were in the market at that time. They included CRT and LCD panels.

At that time, they were considered superior in color reproduction and refresh rates for large televisions and computer monitors. This was until they were replaced by OLEDs which quickly gained traction in the industry.

Applications of major types of displays

With so many devices being manufactured today, there is a need for capable displays to enable interaction with these devices. Most of the types of displays we have discussed above are used to support these devices. Here are some of the common devices that require displays like OLEDs, QLEDs, LCDs, and LEDs

Televisions 

Modern TV set displays are based on different types of displays. You will find LCD, OLED, QLED, and even micro and mini-LED displays. It all depends on the manufacturer and the specific type of TV being made. Basic TVs generally use LED-backlit LCD displays while the high-end versions use QLED or OLED displays. 

Laptops

Laptops require high brightness since the viewing distance is supposed to be small. The majority of displays fitted into laptops are LCD with a backlit. Specifcially most laptop manufacturers use IPS and TN types of LCD displays. Others use OLED too.

Prestigious companies like Apple have announced that they will be using micro and mini-LED for their laptops moving forward. This will make the laptop displays even brighter and more capable per today’s standards. 

Digital signage

The digital signage industry is also benefiting a lot from LED technology. This is why most of them use LED-backlit LCD displays. Digital or outdoor signage does not require high resolution, especially in conditions where they are used for information distribution. Still, this does not mean they are not capable. The backlighting in these displays leads to a bright display.

Large displays

In production studios, events, and exhibitions, organizers have adopted large digital displays for entertainment, education, and decorative purposes. Large displays, as they are collectively called, require display technologies that are capable.

For event backdrops, you need a vibrant display. Therefore, individual OLED or QLED panels can be stacked together to make a large display. The same approach is used for exhibitions, studio spaces, and indoor commercial buildings.

Wearables 

One of the most common wearables today is the smartwatch or smart band. These devices are used for sports and everyday wear. Their functionalities demand mainly PMOLED displays, which is a type of OLED display. PMOLEDs are known for their passive matrix pixel addressing that allows the display to turn on only the required pixels.

Some companies are also creating wearables such as smartwatches with more advanced display technologies such as AMOLED and micro LEDs. Again, Apple is a great example. This company is known for its focus on hardware.

Smart devices 

The range of types of smart devices is increasing as time goes by. That means the need for performant displays is also increasing. Smart devices need bright, clear, and modern display technologies for various reasons. Touchscreen, extreme conditions usage, and high usage are some of these reasons.

Smart devices like smartphones, iPads, home pods, and others are mainly equipped with OLED and AMOLED displays. The choice of the type of display will mainly depend on the specific device manufacturer and their production standards. You will also find entry-level devices that have LCD displays.

Conclusion

The chances are that the best type of display has not been invested yet. Companies are investing a lot of resources in R&D to optimize the current types, while still looking into the future. However, the types that exist today are good enough for current use cases. Probably, display types will get better with time for optimal performance across the board.

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