Mobile phones are the longest-used products in our life, and the average daily use time of each person reaches 4-6 hours, for such an important item that is closely related to life, every time it update, it will pay special attention to the screen material, operating speed, storage size, brand, price, etc., and also consider safety, health, Even the national plot , there have been repeated battery explosions and screen burn events before, so it will be related to the experience for a long time in the future.

This article starts with the basic knowledge of the screen, then introduces the relationship between screen technology and eye protection, and finally two practical cases. In this way, you will have a complete understanding of the knowledge of mobile phone screens. I. Evaluation criteria for mobile phone ,criteria for mobile phone screens include brightness, PPI, contrast, color, response time, display technology and other indicators.

Brightness: an indicator of the intensity of the screen’s luminescence. The brightness is as bright as possible, the height can be adjusted, and it can be clearly seen in the sun. If the screen brightness is low, it will not be seen.

PPI: PPI represents the number of pixels per inch. The screen is made up of pixels like small squares. The higher the PPI value, the higher the density of the display screen. The more delicate the phone screen will look. Most mobile phones have a PPI of more than 300, and the human eye can barely see the graininess.

Contrast: The ratio of the screen’s black to white brightness. The higher the contrast, the darker the black and the brighter the white. Every other color of the response will be more vivid.

Response time: Refers to the speed of screen changes. There is no smear when the screen is switched fast, and smear when the screen is slow.

Color: There are several indicators of color. One is the area of the color, which is called the color gamut. The color gamut is a range of colors, which means that the screen can display the size of the color range in the real world.

The other is the color number, which is the maximum number of colors that a mobile phone screen can display. The greater the number of colors, the more delicate the gradation transitions, and the richer the colors that can be displayed. We usually see 8-bit color, 16-bit color, 24-bit color, and 32-bit color. 24-bit color is called true color, and it can reach the limit of human eye resolution.

The last is the color standard. The color standard is the meaning of the color standard. The color of the screen should meet the standards of the international color system, and there is no deviation in the color.

Although said so much. However, many of these parameters are invisible to the human eye, so it makes it difficult to judge the quality of the screen. However, a screen with good colors must be very comfortable, delicate and clear.

Therefore, we usually say that the color of the screen is good, that is, the judgment made after combining these three indicators. A screen with a large color gamut, a large number of hair colors, and good color accuracy is a screen with good colors.

Second, the mobile phone screen eye protection technology and advantages are simple and clear. There are three main reasons for mobile phone screen eye damage: blue light damage, flicker, personal habits.

1, There are many different wavelengths in nature, and the human eye will recognize them as different colors. The relatively high-energy blue light with a wavelength between 400nm and 440nm is harmful to the human eye and is also the main cause of blue light damage. In mobile phone screens, whether it is an active light-emitting OLED or a passive light-emitting LCD, it will radiate short-wave blue light with a wavelength of 400-440 nanometers.

2, For the problem of eye protection, we mainly talk about the second reason, strobe. Strobe can be simply understood as the screen flicker and hurt the eyes. Although the strobe cannot be seen directly by the naked eye, it can stimulate nerves, cause visual fatigue, and even cause tears and headaches.

The strobe is related to the dimming mode of the mobile phone. At present, the three common dimming modes of the smart phone screen are:

DC dimming

PWM dimming

DC + PWM hybrid dimming

DC dimming

The principle of DC dimming is derived from the formula of “power = voltage * current”, that is, the brightness of the mobile phone screen is changed by adjusting the screen voltage or current. The advantage of DC dimming is that it does not flicker the screen and is relatively green.

PWM dimming

The PWM dimming scheme does not rely on changing the power, but a kind of blinking “light → off → light → off” of a certain frequency on the screen in a very short period of time. Ratio to achieve screen brightness adjustment.

The screen did not really dim or lighten in the process. Instead, it shortens the bright screen time, and makes use of the visual persistence phenomenon of the human eye to give the illusion that the screen seems to be dark.

During the PWM dimming process, if the screen flashes 500 times per second, the frequency of the PWM strobe is 500Hz. The IEEE (Institute of Electrical and Electronics Engineers) points out that LED strobe can cause increased intraocular pressure, migraine, or photosensitivity, and the low-risk health flicker range should be above 1250Hz.

DC + PWM hybrid dimming Another method is DC + PWM hybrid dimming. Select DC dimming at high brightness, and switch to PWM dimming mode only when the brightness is below a certain threshold. Mixing and matching the two is a compromise solution.

Regardless of the previous LCD or OLED, its core appeal is to protect the eyes. DC dimming controls the display brightness by adjusting the screen voltage or current, that is, changing the power. Just adjust the brightness of the backlight directly on the LCD screen, so you can easily achieve global DC dimming. OLED has no backlight, and each pixel emits light independently. If the power is directly adjusted, problems such as color unevenness and color rendering inaccuracy occur at low brightness, so PWM dimming is used.

Therefore, in the current mobile phones on the market, LCD-basically uses DC dimming, OLED-basically uses PWM or hybrid dimming. Although the two dimming methods have their own advantages, from the perspective of eye protection, LCDs with global DC dimming are more healthy.

Two cases

Last year, Iphone XR, Apple released a flagship iPhone XR model, this model uses an IPS LCD screen 6.1-inch LCD full-screen multi-touch display, using IPS technology. 326ppi, 625 nits maximum brightness. According to the test evaluations of users after use, the iPhoneXR LCD screen also does not lose OLED in terms of color, screen sharpness and clarity, reaching the top level. Huawei Honor 20S On September 4, 2019, Honor 20S was released. Considering the habit of eyes of young users for a long time, Honor 20S uses a low-frequency flash LCD screen and passed the TüV Rheinland Low Blue Light certification, which minimized the mobile phone. Screen damage to eyes. The screen of the Honor 20S, with a low-frequency flashing LCD screen, has a color gamut that meets the DCI-P3 standard and PPI 412, which is more delicate and clear in the display effect.

What kind of mobile phone screen eye protection, how to choose a good mobile phone screen, here you should have an understanding. Although the current trend of replacing OLEDs with OLEDs cannot be changed in the application of small-sized screens, LCDs still gain some manufacturers and Users’ favor. In any case, the one that suits you is the best. Some people like gorgeous colors, some people like indifferent landscapes, some people like high-end flagships, and some people like more simple and cost-effective models. . The benevolent sees the benign and the wise. However, in terms of eye protection and health issues, users must keep in mind the following three points during the use of mobile phones: blue light damage, flicker, and personal eye habits.