1. What is PWM

PWM stands for Pulse Width Modulation and is a technology used for adjusting the brightness of displays in various gadgets — from smartphones to televisions. Every screen consists of LEDs that allow you to view images and text. There are two methods to adjust their brightness. The first involves lowering the voltage: the less energy the display receives, the dimmer it will glow. However, this method has a drawback: reducing the voltage affects the image quality.

The second method is PWM, which helps preserve image quality. Instead of reducing the light intensity, the screen simply turns on and off many times per second. For example, it's like quickly flicking a lamp switch. The lower the brightness, the shorter these flashes and the longer the pauses between them. For instance, if the brightness level is set to 30%, then the LEDs will be on for 30% of the time and off for the remaining time.

PWM adjusts brightness by periodically turning LEDs on and off,
and the lower the brightness, the longer the LEDs remain off.

Thus, at 100% brightness, there is no flickering since the LEDs are constantly on and do not turn off. If you lower the brightness to 40–50%, PWM will inevitably appear. The lower the brightness, the more frequent and noticeable these flickers.

However, because the voltage changes at a high frequency, the human eye does not perceive these flickers even with close inspection, creating the impression that the display is lit continuously. The human brain stops detecting flicker at 60 Hz, while PWM frequency is much higher. A rate of 300 Hz and above is considered safe.

So why don't manufacturers completely abandon the use of PWM technology? In fact, it's both technically and economically challenging. Firstly, PWM allows brightness reduction without losing efficiency. Secondly, many believe that PWM better preserves color saturation and black depth when reducing brightness, especially in OLED displays. Thirdly, it is a relatively simple and inexpensive technology. Additionally, digital controllers regulating brightness using PWM are compact compared to analog ones, meaning a smartphone, laptop, or monitor can be made thin and light. All these factors force companies to put up with the shortcomings of the technology.

2. How PWM Affects Health

It is scientifically proven that PWM affects people differently: some are more sensitive to flickering, while others less so. In sensitive individuals, prolonged gadget use can lead to the following problems:

  • dryness, redness, burning sensation in the eyes;
  • headache or even migraine;
  • irritability;
  • fatigue;
  • dizziness;
  • nausea.

Fortunately, significant health harm has not been identified, and all the symptoms mentioned above are temporary. However, if devices with PWM are used for several years, vision might deteriorate.

Prolonged use of gadgets with PWM can cause dryness,
red eyes, headaches, fatigue, dizziness, and nausea.

3. OLED, IPS, AMOLED - Which is Better?

PWM is not used in all screens. The technology is more common in OLED panels (including AMOLED and Super AMOLED). They use organic LEDs, where pixels operate independently and are not connected to each other. In this case, brightness cannot simply be reduced by lowering the brightness of the backlight lamp — there is none, as each pixel serves as an independent light source. Therefore, brightness is adjusted by the duration of pixel illumination, i.e., turning on and off within fractions of milliseconds.

Conversely, IPS screens have a different structure: liquid crystals and backlighting. To reduce brightness, the power of the LEDs can simply be lowered, and flickering will not occur. However, some models still use PWM to reduce construction costs.

Among VA (Vertical Alignment) panels used in televisions, monitors, and some laptops, PWM is relatively rare and mainly found in budget models.

Displays like Mini LED, QLED, and MicroLED installed in televisions, monitors, and laptops also implement Pulse Width Modulation technology, though rarely, and usually with a high frequency.

4. PWM in Smartphones and Tablets

Most modern smartphones and tablets are equipped with OLED, AMOLED, and Super AMOLED displays, so flickering in them is inevitable. It’s important to pay attention to the level of flickering or number of light pulses. A fully safe indicator is considered to be 300 Hz and above, meaning more than 300 flickers per minute — the brain does not recognize them, and accordingly, it doesn't affect health. Unfortunately, in many modern models, this indicator is lower.

A kind of "panacea" is the DC Dimming (Direct Current Dimming) feature, which was first implemented by Xiaomi and picked up by other manufacturers. In this case, brightness decreases by lowering the voltage. It doesn’t completely eliminate flickering, especially at brightness levels below 40%, but the impulses become less active. However, this leads to color distortion and diminished color reproduction.

The DC Dimming function reduces screen brightness by lowering the voltage.
Popular Smartphones with Refresh Rate from 144 Hz

5. PWM in Laptops

Most laptops are based on IPS panels, and among them, there are both models with and without PWM. The rule is quite simple: the more expensive the gadget, the more likely it is to be flicker-free. OLED displays are also widespread, and they almost always have PWM. To minimize discomfort, choose devices with a high frequency level (from 500 Hz). For this, it's advisable to familiarize yourself with tests before buying — many reviewers record the presence of flickering.

Popular Laptops with 300 Hz Screen Refresh Rate

6. PWM in Monitors

The absence of PWM is crucial for working with text, graphics, and gaming since flickering monitors do not facilitate concentration and productivity. The solution is the Flicker-Free technology that eliminates or significantly reduces screen flickering. For this, constant current is used for backlighting instead of alternating current, ensuring stable and continuous LED illumination. Furthermore, some models combine PWM and constant current at a high frequency, thereby reducing flickering to an unnoticeable level.

Flicker-Free technology prevents or significantly reduces screen flickering.

Today, Flicker-Free technology has become standard among many monitor manufacturers and is found in almost all high-quality and professional models. This information is often mentioned in the specifications, and similar indications can be found on the packaging:

We also recommend paying attention to TÜV Rheinland certification. Specialists from the large international corporation conduct screen tests, and their certification confirms a safe level of blue light emission and flickering frequency. In particular, the designation TÜV Flicker-Free (or TÜV Flicker-Free Certified Display) means that there is no harmful PWM at any or most brightness levels, or its frequency is very high and safe for eyesight. This marking indicates the presence of the certificate:

Popular Monitors with Flicker-Free Support

7. PWM in Televisions

In televisions, PWM plays a lesser role because users generally watch screens from a greater distance, leading to less eye strain. However, flickering might be present in dark scenes and at lower brightness levels, particularly on OLED panels. PWM is rarer in LED TVs with IPS matrices.

8. How to Independently Check PWM

Manufacturers do not list PWM information in the specifications, but you can check its presence yourself. First, there are special measuring devices (luxmeter, oscilloscope) used by testers, journalists, and bloggers reviewing technology. Most households likely don’t have such devices lying around, so we offer simpler methods for determining PWM.

The first method is known as the pencil test. Take a pencil in your hand and move it in front of a glowing monitor, like a fan. If the pencil trace is blurred and looks smeared, there is no flickering on the screen. If the trace splits and appears as a set of shadows from multiple pencils, there is PWM on the monitor.

The pencil test is one of the simplest methods for determining PWM.

Conduct tests with different brightness settings to discover which level is safe.

Another simple method is to photograph or record the gadget screen on video. If stripes and artifacts are visible in the frames, this may indicate the use of PWM.

PWM can also be recognized by photographing or recording the screen on video.

9. How to Protect Eyesight

If you are sensitive to screen flickering and experience negative effects of PWM, here are effective ways to take care of your health:

  • choose gadgets with IPS displays;
  • disable automatic brightness adjustment and manually select maximum values (but for this, good lighting indoors or outdoors is required, otherwise eyes will still strain);
  • activate dark mode in the system and applications;
  • take breaks every 30–60 minutes of screen time;
  • opt for devices with Flicker-Free or DC Dimming.

Additionally, there are special filter applications to reduce PWM effects:

  • OLED Saver (for Android) — dims the OLED screen without reducing hardware brightness;
  • Darker (Screen Filter) — an Android app that applies a dark filter;
  • f.lux (Windows/macOS) — changes color temperature depending on the time of day;
  • Twilight — a similar filter for Android smartphones that reduces blue light and makes colors warmer.