With an average of 5.7 screens per household in France according to Arcom, and although we are not the worst students in terms of time spent in front of them, we are surrounded by pixels; smartphones, tablets, televisions and computers monopolize our gaze all day long. All these devices do not have the same purposes, and generally use different display technologies. We have already explained the good reflexes to have when you spend time in front of screens; here, we plan to guide you through this maze of panels.
Two major families of screens
Your TV, your computer screen and your smartphone have a screen belonging to one of the two major families of our time: the first is LCD (Liquid Crystal Display – liquid crystal screen) and the second is OLED (Organic Light-Emitting Diode). That said, if you have an e-reader, it does not belong to any of these lines; its display technique is that of papiel, or electronic paper. And even without an e-reader, you are exposed to it through the electronic labels of stores. However, we are not going to address this subcategory here.
We will detail each of the technologies, but before that, the short video below offered by RTBF iXPé allows you to lay the foundations:
LED screens: reliable and economical
In a file published in 2015, we talked to you about the differences between OLED and LCD screens. More precisely, the interest of OLED compared to IPS, VA and TN panels. Our comments from that time are still relevant, so don't hesitate to take a look.
First of all, let's clear up a potential misunderstanding, conveyed by certain false statements that we have often read here and there while preparing this file: those that we call LED (Light Emitting Diode) screens in everyday language are still LCD screens. They still use a panel with liquid crystals that are oriented according to the electric current. LED screens get their name simply from the fact that unlike traditional LCDs, their backlighting is not provided by CCFL (Cold Cathode Fluorescent Lamp) tubes but by… LEDs. However, the type of backlighting has a direct impact on the brightness and contrast, and therefore ultimately on the quality of the image displayed. LEDs offer increased energy efficiency, better light management (including improved contrast thanks to techniques such as local dimming, a localized adjustment of brightness), as well as a slimmer design.
LCD screens are still widely used today, in a wide variety of devices (computer screens, TVs, smartphones). They are economical and resist wear and tear well. Unlike OLED, static images are not a problem for them; there is no risk of burn-in. Concerning the defects, they are more or less pronounced depending on the type of technology. But compared to OLED, they are less bright, deliver less contrast, duller colors, and their reactivity is also lower.
There are three lines of LCD panels. TN (Twisted Nematic) screens are becoming less and less common but have long been a hit with budget gamers or FPS enthusiasts due to their low cost and their response time, which has long been unmatched for LCDs. On the other hand, they reproduce colors poorly and suffer from limited viewing angles.
On the other hand, IPS (In-Plane Switching) guarantees better color reproduction, as well as wider viewing angles than TN. This, at the expense of response time, and at the cost of a larger budget.
As for VA (Vertical Alignment) panels, they represent a good compromise between contrast, viewing angles, responsiveness and price.
All these names reflect the alignment of the crystal molecules inside the screen, and the way they change when they are electrically charged.
In all cases, an LCD screen is based on a tangle of layers. The first is therefore that of the backlight, which provides the main source of light. It passes through a layer sandwiched between two polarizing filters, one vertical, the other horizontal, of liquid crystals that react to electric fields (these crystals change orientation, blocking or limiting the light coming from the backlight, depending on the electric field applied). Generally speaking, the coloring is done from three primary colors: red, green, blue (the famous RGB). Each pixel is thus composed of three cells (or sub-pixels).
To return to backlighting, manufacturers can opt for Full LED / Direct LED or Edge-LED, detailed below. But the fundamental principle does not change. Backlighting can be done globally or by zones. Note that the LED type may also vary.
Now well mastered and regularly improved, this technology is economical and reliable. However, due to the very principle of backlighting, blacks can lack depth, while conversely, brightness can be insufficient in certain environments.
Nowadays, some manufacturers (Samsung, Hisense and TCL) offer televisions stamped QLED (Quantum Dot Light Emitting Diode), LG Super UHD (Color Prime) and Sony Triluminos (Color IQ). Don't be fooled, despite the resemblance to OLED, these are indeed LCD models. They are only improved thanks to a Quantum Dots technology.
The principle: the addition of an additional filter based on nanocrystals (quantum dots) capable of emitting a precise colored light when exposed to the light of the LED backlight. This improves the brightness and better renders colors, especially those based on red and green, than a standard LED screen. But you will have understood, it is only an optimization, and not a change in nature as with OLED.
Also integrated into the large LCD family, the Mini-LED panel branch uses a multitude of very small LEDs. The aim is to increase the density of the LED checkerboard and thus refine the backlighting by zones. These thousands of mini-LEDs increase the precision of the targeting, and therefore greatly improve the brightness and contrast. That said, the inherent defects of LED screens are not completely erased. You will come across Mini-LED screens under different names; QNED at LG, Neo QLED at Samsung. And you will have understood, Mini-LED and Quantum Dot quantum dots very often, if not systematically, go hand in hand.
OLED: exit the backlighting
It’s time to move on to OLED. Here again, the name, Organic Light-Emitting Diode, gives the color: OLED screens use organic light-emitting diodes. The basic structure consists of a superposition of several layers (a hole transport layer (HTL), an emission layer (EML) and an electron transport layer (ETL)) arranged between a cathode and an anode. Each pixel of such a screen emits its own light; it is self-emissive. Unlike LCD screens, these panels therefore do not require any backlighting. As a result, and since each pixel can be turned off individually, these screens deliver the best contrasts, with absolute blacks; they are extremely responsive and spared from ghosting; offer wide viewing angles; are the most energy-efficient.
The drawbacks of the technology are the risk of marking (burn-in) combined with a theoretically shorter lifespan than LCDs. That said, manufacturers are working hard to circumvent these phenomena. The real obstacle is that these screens remain expensive today. However, they are increasingly equipping smartphones, but are still limited to high-end televisions (although they are logically tending to become more democratic over the years).
Concerning the names, there are several. The "basic" OLED is based on a classic RGB system with three diodes (Red, Green, Blue). To get white, all three light up. Unfortunately, the organic compounds used for each sub-pixel age at different rates (blue OLED has a much shorter lifespan). To counter this phenomenon, panel manufacturers LG Display and Samsung market WOLED and QD-OLED panels respectively.
WOLED, for White OLED, also called WRGB, for White Red Green Blue, adds a fourth diode, and all are white. Three are covered with filters (red, green and blue), while the other is not in order to let white light pass directly. The problem with this strategy is that the color filter blocks some of the light. This results in “diluted” colors compared to whites and a reduction in energy efficiency.
Samsung’s QD-OLED uses a blue OLED base as its main light source. As the company explains on its website, the light-emitting diodes therefore emit exclusively blue light, which is then diffused onto a layer of nanoparticles that we have already discussed above (in English “Quantum Dot Color Converter”). These Quantum Dots convert blue light into other colors. As with LED screens, these quantum dots are more efficient than filters at converting light. The underlying OLED emitting layer does not need to be overstressed, while the colors are better rendered.
However, for a few months now, Samsung has been content to qualify its new OLED screens. The Korean brand markets some of its screens with QD-Oleds, others with W-Oled panels purchased from LG. Economic and logistical reasons are put forward to justify this choice.
In addition, other alternatives are flourishing. Let us mention the phOLED, for phosphorescent Organic Light Emitting Diode, which, unlike the classic OLED – which should be called here FOLED (Fluorescent OLED) to understand the difference – uses phosphorescent rather than fluorescent materials, which benefit from much higher energy efficiency.
To conclude this article, let's talk about one last branch of OLED: Micro-LED, once presented as the future of screens. Still immature and very expensive, it is an emerging technology for miniaturizing OLED similar to that of Mini-LED for LED screens. On the other hand, unlike OLED, Micro-LEDs are made of an inorganic material (gallium nitride). As a result, they benefit from a longer lifespan and do not present any risk of burn-in. We will certainly be talking about it again in a few years.
OLED vs LCD, advantages and disadvantages
The table below will provide you with a summary of the main characteristics to remember. Of course, the choice of a screen technology depends heavily on the intended use, but also on the budget you are willing to agree to.
| Technology | Blacks | Colors | Brightness | Costs | Lifespan | Applications |
|---|---|---|---|---|---|---|
| OLED | Perfect | Excellent | Average | High | Moderate | High-end televisions, smartphones |
| WOLED | Good | Good | High | Moderate | Moderate | Premium TVs |
| QD-OLED | Perfect | Exceptional | High | Very high | Good | Ultra-high-end TVs and monitors |
| LCD (IPS) | Good | Average | Medium | Low | Long | Monitors, PC portable |
| Micro-LED | Perfect | Excellent | Very high | Extreme | Long | Professional TVs and displays |
| Mini-LED | Good | Good | High | Moderate | Long | TVs and monitors |
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