As feature phones transitioned into the era of smartphones, we have experienced one revolution after another in screen sizes, from the initial 1-inch monochrome displays to the now commonplace 6.0-inch screens. The mission of mobile phones has evolved from simple calls and texts to a gateway for everyone to connect with the world.
Undoubtedly, more and more time is occupied by this small space. According to a report by market research firm Statista, last year it was revealed that Chinese users spend an average of over 3 hours daily on their mobile phones, and this time has only increased as we moved into 2018.
Perhaps it is precisely because mobile phones have become the most important personal device globally that the impact of smartphones on human health has become a focus of concern for many. In various discussions among major smartphone players, you often hear claims about OLED screens being harmful to the eyes, with PWM low-frequency dimming often cited as the primary culprit.
As the iPhone gradually embraces OLED technology, with almost all flagship products now catering to OLED users, I believe everyone is eager to know whether this display, known for its vibrant colors, truly has a greater impact on vision.
PWM Low-Frequency Dimming Has Original Sin
We all know that AMOLED displays are made of self-emissive organic materials and do not require an LCD backlight. When current flows through the organic material, the pixels emit light on their own. Therefore, compared to LCD screens, AMOLED has advantages such as purer blacks and higher contrast.
However, being more ‘ideal’ also means paying a higher price.
The claims about AMOLED displays being harmful to the eyes stem from dissatisfaction with the widespread use of PWM low-frequency dimming by current AMOLED manufacturers. Here, I will briefly explain PWM low-frequency dimming technology.
All displays have brightness adjustment functions, but due to material differences, the dimming technologies vary. Currently, the most mainstream methods in smartphones are DC dimming and PWM dimming.
LCD screens rely on LED backlights to emit light, and thus, most LCD screens in the smartphone field use DC dimming, a method that adjusts brightness by directly controlling the current flowing through the light-emitting components. As the current on both sides of the LED backlight decreases, the brightness also decreases.
DC dimming is a very direct method but has significant drawbacks. Due to the differing wavelengths of the three primary colors, DC dimming can lead to unavoidable color distortion at extremely low brightness levels. For instance, early LCD displays that used DC dimming exhibited noticeable color loss at low brightness.
DC dimming is not well-suited for AMOLED screens. As mentioned earlier, AMOLED displays rely on organic materials to emit light, so their display quality is directly related to the quality control of the screen materials, leading to very noticeable color differences between pixels.
With DC dimming, early models like the Galaxy S, S2, and Note experienced uneven whites and severe color distortion.
In fact, this issue has not been well resolved even now. A developer on the XDA forum released a kernel to forcibly enable DC dimming mode on the Galaxy S8, which still exhibited the aforementioned problems when the brightness was below 20%.
▲ The so-called ‘cloth screen’ effect
Perhaps it is for this reason that PWM dimming has become another option and has entered everyone’s sight.
Unlike DC dimming, which directly adjusts the current to control brightness, PWM dimming operates more cleverly. We know that switching the light source causes flickering. The faster the switching speed, the faster the flicker of the screen.
However, when the switching frequency of the light source exceeds the human eye’s limit, all brightness information on the screen overlaps in the human eye, so the speed of the frequency only affects the screen’s brightness. This technology, which adjusts brightness through rapid switching of the screen light source, is called PWM dimming (Pulse Width Modulation).
PWM dimming has solved the early low-brightness color distortion issues of AMOLED displays and has further improved color stability.
However, since PWM dimming is a technology that adjusts brightness through rapid flickering, even though the human eye cannot perceive the switching process, our brains react to this phenomenon. Frequent flickering can lead to fatigue in the muscles around the eyes, stimulating the refractive system and accelerating vision aging.
Currently, all AMOLED displays produced by Samsung use a low-frequency PWM dimming technology of 250Hz. As the screen brightness decreases, the flickering rate also decreases, making it more likely for sensitive individuals to perceive it, thus causing greater impact.
This is the inherent flaw of PWM low-frequency dimming technology.
You Think AMOLED Screens Hurt Your Eyes?
But Actually, LCD Screens Aren’t Immune Either
Long-term use of AMOLED displays with PWM low-frequency dimming does seem to impact vision. However, don’t think that LCDs are immune to this issue. Even with DC dimming, they also have irreversible effects on vision — you cannot ignore the harm of blue light.
Unlike the self-emissive mode of AMOLED, LCD screens use a combination of backlight + optical filter for imaging. In mainstream technology, many LCD screens use blue LED backlights, which are covered by red, green, and clear optical filters. When blue light passes through these three filters, it forms RGB primary colors.
Among these, the blue backlight emits light that contains concentrated short-wave blue light energy density, which can cause harm when humans’ eyes are exposed to it for long periods at close distances.
In fact, short-wave light is constantly present in nature. Although it is invisible, it enters the human eye through the lens and images on the retina like other light.
Due to the greater energy density and strong penetrability of short-wave light, it can directly penetrate the lens and reach the retina, leading to the atrophy or even death of retinal pigment epithelial cells, which is the culprit of macular degeneration.
For children, this harm is undoubtedly greater. It is known that the human lens absorbs some blue light and gradually becomes cloudy, leading to cataracts. Children’s lenses are clearer and cannot effectively block blue light like adults, making the impact of blue light on children more severe.
The Technology Itself Is Not Wrong; Usage Habits Matter More
From a medical perspective, the eyes, as one of the organs of the human body, consume their functionality even with normal use. The decline in vision often does not stem from the technology or the object itself, but rather from abnormal daily habits.
From the above technical analysis, it is not difficult to see that, in terms of technology, whether it is LCD or AMOLED, the impact on vision is universally present. At least in the smartphone field, it is hard to say which screen is more harmful.
▲ Is LCD or AMOLED more harmful? This itself is a false proposition.
Even if the LCD faction raises the banner that PWM low-frequency dimming is harmful, it cannot completely prove that AMOLED screens affect vision because everyone’s habits in daily life, eye hygiene, and personal perception of screen brightness and color will vary. These factors can lead to feelings of comfort or discomfort.
Undoubtedly, what needs to be noted is still the usage habits. For example, users should try to avoid staring at their mobile phone screens for long periods; reduce viewing time at low brightness levels for both LCD and AMOLED in dark environments; if you have a habit of reading at night, you should also turn on another light source to mitigate flicker; and use eye drops to moisturize your eyes when they feel dry, etc.
The cosmic theorem dictates that time can only move forward and cannot go back. The advancement of technology brings more convenience to life, and it will inevitably change the living laws that humanity has adapted to for thousands of years.
In today’s world, where mobile payments, fragmented reading, and social interaction all depend on mobile phones, the market will pose new challenges for us. According to Samsung’s official estimates, thanks to eye-catching color display effects.
By 2020, AMOLED will occupy almost all high-end market shares, and the overall market penetration will reach 65%. I wonder if the LCD faction will be ready to give up using high-end phones by then?
It is never the technology that is wrong, but rather the human conviction itself. Don’t let foolish fundamentalism take away your opportunity to understand the new world.
“Order a good bottle of eye drops first~”
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