Are there differences between different mobile phone screens? Choose the right one and it won’t hurt your eyes!

Review expert: Zhou Hongzhi, senior laboratory technician, master's supervisor, School of Physics and Optoelectronic Engineering, Beijing University of Technology

Do your eyes feel sore and uncomfortable after looking at your phone for a long time? Do you know that different models of mobile phones have different screen lighting principles? Choosing a mobile phone screen that suits you can protect your eyes more effectively.

Smartphones are constantly being updated and upgraded, and smartphone screen technology is also developing rapidly. Upgrades in refresh rate, resolution, dimming and other dimensions are constantly optimizing the mobile phone display experience. Do you know the differences between different mobile phone screens? Come and see which one your phone belongs to!

0 1 Common types of mobile phone display panels

Currently, mainstream mobile phone screens are divided into two categories, each of which contains multiple sub-technologies:

LCD screen: Liquid Crystal Display

OLED screen: Organic Light Emitting Diode

LCD screen

The LCD screen uses the display principle of a combination of liquid crystal molecules and a backlight layer. Its pixels do not emit light themselves, but rely on backlight illumination, and the amount of light passing through is controlled by the rotation angle of the liquid crystal molecules, and the color changes are formed in conjunction with the color filter.

This type of screen has a stable structure and is less likely to have afterimages when displaying static images for a long time. It also generally uses a flicker-free DC dimming mode, which is more eye-friendly at low brightness.

However, due to the need to stack the backlight layer and the liquid crystal layer, the screen is thicker overall and cannot be flexibly bent, and the color performance and viewing angle are usually weaker than self-luminous OLED. Since the backlight is always on, even when displaying black, the light needs to be blocked, making the contrast relatively limited, and dark details may appear gray.

LCDs are eye-friendly and suitable for displaying fixed content for a long time due to their reliability and flicker-free characteristics, but they are limited in picture quality, image sharpness and thin and light design.

Image source: ZTE Documents

At present, the LCD screen technology has been very mature and its price is relatively cheap compared to other screen materials, so its market share and popularity are higher. We can also understand that LCD screens are the market leaders of early mobile phone screens.

However, since its light is emitted by the backlight layer through refraction, the screen is relatively thick and hard. In order to overcome the shortcomings of LCD, people have developed a new display screen: OLED.

OLED screen

Before introducing OLED screens, let us first understand the concept of LED.

LED stands for light-emitting diode, which is an imaging electronic device that can emit light. According to the purpose of use, light-emitting diodes are arranged in sequence of red, green and blue colors, and a control signal is applied to convert electrical energy into light energy. It is called the fourth generation of light sources. It is widely used in general lighting and other fields, such as traffic lights, decorations, etc.

OLED stands for organic light-emitting diode, which is mainly composed of display units and light-emitting materials. It consists of three independent light-emitting diodes, red, green and blue, to form independent pixels. These organic materials will generate light by themselves when driven by electric current, without the need for additional backlight.

Image source: ZTE Documents

When displaying black, the corresponding pixels are completely powered off, so pure black and high contrast can be achieved. This type of screen activates fewer pixels when displaying dark images, and consumes less power. The high brightness itself achieves more vivid colors and greater brightness dynamics.

At the same time, the screen can be made thinner and lighter, using a flexible substrate to support bending and folding.

However, due to the limited lifespan of organic materials, if a fixed image (such as a status bar icon) is displayed at high brightness for a long time, some sub-pixels will have residual images due to aging, which is called "screen burn-in". In addition, the method of adjusting brightness by quickly switching pixels on and off at low brightness (PWM, or pulse width modulation dimming) may cause eye fatigue.

0 2What do dimming and strobe mean?

Dimming is a technology that controls the brightness of the screen, which is mainly divided into DC (direct current dimming) and PWM (pulse width dimming).

Simply put, the former changes the screen brightness by adjusting the current; while the latter changes the screen brightness by controlling the screen's light and dark time.

DC dimming: Directly changing the output intensity of a light source (such as an LCD backlight or OLED pixel) by adjusting the current or voltage. When the brightness is reduced, all working units (such as LED lamp beads) continue to emit light but become dimmer.

This method has no flicker, but the LCD may have color deviation or uneven backlight at low brightness.

PWM dimming: Brightness changes are achieved by quickly switching the light source on and off (hundreds to thousands of times per second) and using the visual aftereffect of the human eye to mix the light and dark time ratios (the duty cycle of high and low levels).

For example, at a 1:1 duty cycle, if the screen operates at 240 on-off times per second, with power on for 50% of the time (120 times high level, luminous), and power off for 50% of the time (120 times zero level, no light), the actual perceived brightness is close to half of the full brightness.

Flickering is a side effect of PWM dimming. When the screen brightness is reduced, the proportion of "power off" in the switching cycle increases (for example, at low brightness, it becomes 80% off and 20% on), resulting in a more noticeable alternation of light and dark.

The human eye's sensitivity to flicker is frequency-dependent:

High-frequency PWM (e.g. above 2000Hz): The human eye can hardly detect flicker, and the visual experience is smooth;

Low-frequency PWM (such as 240Hz): It is easy to perceive fluctuations in light and dark. Long-term use may cause eye soreness and fatigue, especially for sensitive people.

LCD uses DC dimming by default, and some models may turn on PWM only at extremely low brightness, but the overall flicker risk is low; OLED relies on PWM dimming due to the pixel brightness characteristics, and high-frequency PWM or DC-like solutions (supported only by some manufacturers) can be used to reduce the impact of flicker.

0 3Selection suggestions

If you have severe eye protection needs, you can give priority to high-frequency PWM, DC-like OLED, or high-quality LCD models, preferably with an anti-blue light mode.

If you want to balance better display effects and eye protection needs, you can choose high-frequency PWM OLED and avoid low-brightness scenes.

The most important thing is: although high-frequency PWM technology is basically adopted at the current technological level, in order to protect the eyes, it is still necessary to develop good operating habits: reduce use in dark environments, use auxiliary light to reduce the degree of pupil opening, or turn on automatic brightness adjustment, and close your eyes and rest regularly.