Understanding Display Technologies: LCD, OLED, MiniLED, MicroLED

When it comes to displays, everyone is familiar with them. We interact with electronic products every day, from smartwatches to large advertising screens, all of which rely on displays. But how much do you really know about displays? Let’s take a step forward and get to know the screens in our hands.

For display devices like phones and computers, images are made up of numerous small pixels. Each pixel consists of red, green, and blue sub-pixels, which are the three primary colors we know. By mixing these primary colors in different proportions, we achieve the colors we need. The vast number of pixels come together to form the images we see.

LCD generally stands for Liquid Crystal Display, which uses CCFL (Cold Cathode Fluorescent Lamp) as the light source.

Structure of a single pixel

To facilitate understanding, you can imagine the liquid crystal layer as a set of adjustable blinds. When powered, the backlight layer at the bottom emits white light, while the voltage from the positive circuit penetrates the liquid crystal layer, forming a circuit with the negative circuit. The voltage controls the deflection angle of the liquid crystal molecules, similar to controlling the blinds, thereby controlling the brightness of the white light passing through the primary colors. By changing the proportions, we mix the colors we need. This is how LCD works. It’s important to note that the backlight layer of an LCD screen is a large shared layer for all pixels.

My iPad Pro uses an LCD screen magnified 120 times

OLED stands for Organic Light Emitting Diode. Each pixel is also composed of red, green, and blue sub-pixels, but it does not require a backlight layer, polarizer, or liquid crystal layer. It lights up when powered, and the color ratio of each sub-pixel is controlled by the power supplied, allowing for various colors to be displayed.

My Samsung Note 10+ uses an OLED screen magnified 120 times

My iPhone 12 Pro Max uses an OLED screen magnified 120 times

Unlike LCD’s backlight layer, OLED can control the switch of each pixel individually without lighting up the entire backlight layer, which is a significant advantage of OLED. For example, when displaying a completely black image or a background that is entirely black, LCD requires all liquid crystal molecules to be fully closed, which is not achievable in practice. Therefore, LCD screens display a dark gray instead of true black, while OLED can turn off all pixels completely, achieving true black.

Left is the OLED screen of Xiaomi 10u, right is the LCD screen of iPhone 8 Plus

This leads us to the second advantage of OLED screens: theoretically, they can achieve infinite contrast. Contrast is the ratio of brightness between dark and light areas in an image, and it is an important indicator of display quality. Due to inherent disadvantages, LCD cannot light up specific pixels like OLED does, resulting in significantly lower contrast. Additionally, the individual light-emitting feature of OLED enables functions like AOD (Always On Display), which allows certain pixels to emit light while the phone is locked, achieving the desired display effect.

My X70 Pro+’s AOD display effect

Compared to LCD, OLED also has advantages such as fast response time, not being affected by temperature, thin design, the ability to use COP packaging, some degree of bending, and low power consumption.

However, the disadvantages of OLED screens cannot be ignored. The most significant drawback is their short lifespan. The frequent migration of electrons in organic light-emitting diodes leads to a lifespan that is significantly shorter than that of LCD screens. After some sub-pixels age too quickly, we often encounter the phenomenon known as “burn-in,” which is essentially a color difference caused by uneven aging of the pixels. To avoid burn-in as much as possible, we should avoid prolonged high-brightness displays of static images on OLED phones. Manufacturers have also implemented pixel shifting techniques to prevent burn-in from static icons like notifications by slightly moving the static icons over time, achieving the desired display effect without accelerating the aging of specific pixels.

Another major drawback is the dimming method. LCD uses DC dimming, directly controlling the brightness of the backlight layer through voltage adjustments; PWM dimming controls brightness by adjusting the on/off duty cycle, which simply means turning on and off rapidly. If the frequency is high enough, it achieves a “constant on” effect without affecting the display quality. However, if the frequency is too low, it can cause discomfort due to flickering. Due to OLED’s characteristics, it can only use low-frequency PWM dimming, which is one reason many users feel dry eyes and discomfort after using OLED phones. Currently, mainstream OLED screens generally use low-frequency PWM dimming, but it’s worth noting that the domestic screen manufacturer BOE has developed high-frequency PWM dimming OLED screens and has achieved mass production.

Magic 4 promotional material

So, is the LCD screen better for your eyes? Not necessarily. The light emitted by screens that is most harmful to the eyes falls within the 420-440 nm wavelength range of blue light. A considerable portion of the blue light emitted by LCDs is within this range, while OLED screens, represented by Samsung’s AMOLED, have shifted the blue light wavelength to the right through several generations of material updates. Official data shows a reduction of about 42% in blue light, significantly reducing harm to the eyes. Therefore, there is no definitive statement that one type of screen is better for the eyes; to protect your vision, it’s more effective to simply reduce mobile phone usage.

MiniLED is currently a transitional solution. Unlike traditional LCDs with a whole backlight layer, it divides the backlight layer into many zones to improve local contrast. Essentially, it is not much different from LCD screens and is currently only adopted in some high-end televisions (direct backlight, zone backlight) and mobile devices (iPad Pro 12.9). Its drawbacks are also evident; when displaying locally bright images, there can be significant halo effects at the edges, similar to light leakage, which affects the display quality. Additionally, MiniLED, due to the addition of numerous independently controlled LED beads, cannot be ignored in terms of thickness and heat generation, often requiring additional active cooling. For this reason, MiniLED cannot become mainstream and serves only as a transitional technology.

MicroLED, which has not yet been mass-produced, is the future of screens. Compared to LCD, MicroLED eliminates the polarizer, liquid crystal layer, and filter, replacing the entire backlight layer with independently controlled LEDs corresponding to the three primary colors.

This means that the display principle of MicroLED is essentially the same as that of OLED, except that the organic light-emitting diodes in OLED are replaced with inorganic LED beads. Since there is no entire backlight layer or liquid crystal layer, and it can control the switch and brightness of individual pixels just like OLED, MicroLED inherits all the advantages of both LCD and OLED. Currently, the drawback of MicroLED is that it cannot be produced on a large scale using chemical vapor deposition like OLED. Each MicroLED bead must be independently planted, leading to a significant increase in production costs. Therefore, it is not yet mass-produced, and very few products are equipped with it, and those that are are very limited in number.

As we interact with screens every day, have you ever thought about how a small screen is the culmination of so many advanced technologies? From LCD to OLED, and now to MicroLED, each generation’s birth is almost revolutionary. Let’s look forward to the arrival of MicroLED together.

Some text sources: bilibili.com/BV1Wz411B7Tf

Some image sources: JD.com, Honor Mall, bilibili.com

Text and image editing: Hu Xianju

This article is an assignment for Tianjin University’s “History of Science and Technology” course.

The images in this article are mostly sourced from the internet. If there are any infringements, please contact the author for deletion.

Thanks to Professor Chen Yinzhen for the guidance! Thank you for reading!