The OLED displays consist of self-luminous organic materials. Unlike the LCD display, which uses backlight, they have their own source of light. So these types of screens offer better contrast ratio than the LCD displays. Apart from that, OLED displays also portray amazing colors with deeper blacks. That’s why OLED displays are quite popular in the market. And in that context, the AMOLED displays are often remarked best because of their ability to showcase punchy colors with an astounding level of brightness. But while staying indoors and using smartphones during night time, we require a lower volume of brightness. And while lowering the display brightness, smartphones use either one of the two methods of dimming the display. And one of them is so fatal that it can create eyestrain, which can further proceed to trigger migraine and other health-related issues.
PWM Dimming
PWM actually stands for pulse width modulation. And it is one of the widely used display dimming technologies in the market. As the name implies, this technology varies the light pulse in the display to alter the amount of brightness in the screen. In this technology, the display brightness is adjusted by altering the on-time and off-time of the display. The display glows on full brightness but since the on-time and off-time are varied, human eyes perceive the average brightness that appears in the screen for the time. Higher the on-time, higher would be the brightness. Lower the on-time (or higher the off-time), lower would be the screen brightness.
Here is a pulse waveform, which can give a clear idea on the topic:
As shown in the diagram above, when the brightness of the display is 100%, the screen remains on all the time. But when the brightness is dropped down to 50%, the on-time decreases. It remains on for 50% of the time and off for the remaining time. And the screen will toggle between these modes at a very high frequency, which can be indistinguishable to the human’s naked eyes.
Source: OLED-info
You might have got the point that on decreasing the brightness further, the off-time increases as well. But while decreasing the display brightness at extremely lower levels, the off-time will be very high when compared with the on-time. And in that case, there will be a considerable flicker effect.
Disadvantages of PWM Dimming and Screen Flickering
Even at extremely lower values, the screen flickering won’t be yet noticeable to our eyes. Nonetheless, it will still create all sorts of discomforts. The PWM Dimming can arise distresses like eyestrain and headaches in the earlier phase and can even trigger migraines after long-term exposures. But researchers found that only 10% of the population are gravely affected with the PWM Dimming. Rest of the people either would be completely okay or would notice just mild discomforts because of it. But for those who get affected, the PWM dimming can cause other health-related issues as well.
The PWM Dimming is a digital means of adjusting the brightness. Although it is cost-effective, it has its own sorts of flaws. And to overcome the issues related to PWM Dimming, an analog means of display dimming technology was discovered. And it goes by the name of DC Dimming.
DC Dimming
To light the backlight of the LCD and tiny LEDs of the OLED display, it requires a power source. And while studying about the electricity, we learned power as the product of voltage and current (Power = Voltage x Current). So varying any of this quantity, we can control the power supply to the display and adjust the brightness. Although it sounds simple on the words, it is not that simple after all.
Source: Sparrows News
This technology was used on LCD displays in the past. But on the OLED displays, it hasn’t been much. Smartphone manufacturers have recently started to roll out this feature on their handsets. It was because of one major downside of the technology on OLED displays, which had caused smartphone makers not to use it much. While adjusting the display brightness to the lower values, the current/voltage supplied to the display decreases significantly. And this considerate decrease on the voltage/current won’t be sufficient to light all the RGB LEDs properly. So the colors portrayed by the screen usually vary from their true colors. The colors emitted by the screen can also change beyond identifiable limits at times, which could even change the way users perceive the quality of the display.
The optimum solution
To counteract the downsides of both of these technologies, smartphone makers have started providing both of these features on the OLED panels these days. The brightness of the display lowers using PWM Dimming technology by default. And they include DC Dimming as an add-on feature on the setting. Those who get affected by the screen flickering issue due to PWM dimming, they can trigger the DC Dimming feature on and stay safe from the health hazards.
To address the issue, OnePlus rolled out a software update, which included DC Dimming feature on its latest devices. Xiaomi did the same with its popular devices like MI 8 and MI 9. Another Chinese company, Oppo, also made its Oppo Reno smartphone compatible with this feature. Since this feature is directly connected with the users’ health, other smartphone companies are also following the suit. Apart from the aforementioned brands, we have heard Vivo and Meizu working on it. So it might be a mainstream feature in all the smartphones in a year or two. But as of now, choose the smartphone display wisely if you are sensitive with the phone’s displays.
