Although there are big differences between LCD and LED displays, there are a lot of confusion in the market which shouldn’t happen. Part of the confusion comes from the manufacturers. We will clarify as below.
LCD Displays vs LED Displays
LCD stands for “liquid crystal display”. LCD can’t emit light itself; it has to use a backlight. In the old days, manufacturers used to use CCFL (cold cathode fluorescent lamps) as backlight, which is bulky and not environment friendly. Then, with the development of LED (light emitting diode ) technology, more and more backlights use LEDs. The manufacturers name them as LED monitors or TV which makes the consumers think they are buying LED displays. But technically, both LED and LCD TVs are liquid crystal displays. The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light. So really, LED TVs are a subset of LCD TVs.
Quantum Dot Displays
Quantum-dot TVs are also widely discussed for recent years. It is basically a new type of LED-backlit LCD TV. The image is created just like it is on an LCD screen, but quantum-dot technology enhances the color.
For normal LCD displays, when you light up the display, all the LEDs light up even for unwanted area (for example, some areas need black). Whatever perfect the LCD display made, there is still small percentage of light transmitting through the LCD display which makes it difficult to make the super black background. The contrast decreases.
Quantum-dot TV can have full-array backlit quantum-dot sets with local-dimming technology (good for image uniformity and deeper blacks). There can be edge-lit quantum-dot sets with no local dimming (thinner, but you may see light banding and grayer blacks).
Photo-emissive quantum dot particles are used in RGB filters, replacing traditional colored photoresists with a QD layer. The quantum dots are excited by the blue light from the display panel to emit pure basic colors, which reduces light losses and color crosstalk in RGB filters, improving display brightness and color gamut. Although this technology is primarily used in LED-backlit LCDs, it is applicable to other display technologies which use color filters, such as blue/UV AMOLED(Active Matrix Organic Light Emitting Diodes)/QNED(Quantum nano-emitting diode)/Micro LED display panels. LED-backlit LCDs are the main application of quantum dots, where they are used to offer an alternative to very expensive OLED displays.
Micro LEDs and Mini LEDs
Micro LED is true LED display without hiding at the backside of the LCD display as backlight. It is an emerging flat-panel display technology. Micro LED displays consist of arrays of microscopic LEDs forming the individual pixel elements. When compared with widespread LCD technology, micro-LED displays offer better contrast, response times, and energy efficiency.
Micro LEDs can be used at small, low-energy devices such as AR glasses, VR headsets, smartwatches and smartphones. Micro LED offers greatly reduced energy requirements when compared to conventional LCD systems while has very high contrast ratio. The inorganic nature of micro-LEDs gives them a long lifetime of more than 100,000 hours.
As of 2020, micro LED displays have not been mass-produced, though Sony, Samsung and Konka sell microLED video walls and Luumii mass produces microLED lighting. LG, Tianma, PlayNitride, TCL/CSoT, Jasper Display, Jade Bird Display, Plessey Semiconductors Ltd, and Ostendo Technologies, Inc. have demonstrated prototypes. Sony and Freedeo already sells microLED displays as a replacement for conventional cinema screens. BOE, Epistar and Leyard have plans for microLED mass production. MicroLED can be made flexible and transparent, just like OLEDs.
There are some confusions between mini-LED used in LCD backlight as Quantum dot displays. To our understanding, mini-LED is just bigger size of micro LED which can be used for larger size of cinema screen, advertisement walls, high end home cinema etc. When discussing Mini-LED and Micro-LED, a very common feature to distinguish the two is the LED size. Both Mini-LED and Micro-LED are based on inorganic LEDs. As the names indicate, Mini-LEDs are considered as LEDs in the millimeter range while Micro-LEDs are in the micrometer range. However, in reality, the distinction is not so strict, and the definition may vary from person to person. But it is commonly accepted that micro-LEDs are under 100 µm size, and even under 50 µm, while mini-LEDs are much larger.
When applied in the display industry, size is just one factor when people are talking about Mini-LED and Micro-LED displays. Another feature is the LED thickness and substrate. Mini-LEDs usually have a large thickness of over 100 µm, largely due to the existence of LED substrates. While Micro-LEDs are usually substrate less and therefore the finished LEDs are extremely thin.
A third feature that is used to distinguish the two is the mass transfer techniques that are utilized to handle the LEDs. Mini-LEDs usually adopt conventional pick and place techniques including surface mounting technology. Every time the number of LEDs that can be transferred is limited. For Micro-LEDs, usually millions of LEDs need to be transferred when a heterogenous target substrate is used, therefore the number of LEDs to be transferred at a time is significantly larger, and thus disruptive mass transfer technique should be considered.
It is exciting to see all the kinds of display technologies which make our world colorful. We definitely believe that LCD and/or LED displays will pay very important roles in the future metaverse.
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