What Is PWM Flicker and Why Does It Cause Headaches?

2026-01-10

Quick Answer

PWM (Pulse-Width Modulation) is a backlight dimming method that switches the light on and off rapidly. Some people are sensitive to this flicker and experience headaches or eye strain, especially at lower brightness settings.

What is PWM?

PWM stands for Pulse Width Modulation. Many displays use PWM to control brightness by rapidly turning the backlight on and off. At 50% brightness, the light is on half the time and off half the time. The switching happens so fast that your eyes perceive it as a steady, dimmer light.

The problem: if the switching frequency is too low, some people can perceive the flicker. Even those who cannot consciously see it may experience eye strain, headaches, and fatigue from the constant rapid light changes.

At what frequency is PWM a problem?

Below 250Hz: Problematic for many people. Some can consciously see the flicker, and many will experience discomfort.

250Hz to 1000Hz: Below the conscious perception threshold for most people, but can still cause eye strain in sensitive individuals during extended use.

Above 1000Hz: Generally considered safe for nearly everyone. High-frequency PWM behaves similarly to a continuous light source as far as your eyes are concerned.

DC dimming (no PWM): The ideal solution. Some monitors dim the backlight by reducing voltage directly rather than flickering. This eliminates PWM entirely.

How to test for PWM

Use our PWM Test to check for visible flicker. You can also use the pencil test: wave a pencil quickly in front of your screen while displaying a white background at low brightness. If you see multiple distinct shadows of the pencil rather than one smooth blur, your display uses low-frequency PWM.

Symptoms of PWM sensitivity

Headaches that develop during or after screen use

Eye strain that worsens at lower brightness levels

Sensation of eyes feeling tired or dry faster than usual

Occasional nausea during extended screen use

Solutions

If you suspect PWM is causing issues, try increasing your screen brightness (PWM is usually most aggressive at low brightness levels). Use bias lighting behind your monitor so you can raise the ambient light level without needing low screen brightness. If possible, switch to a monitor that uses DC dimming or high-frequency PWM above 1000Hz.

Frequently Asked Questions

Does PWM actually cause headaches?

Yes, in people who are sensitive to it. Research and widespread user reports confirm that low-frequency PWM (under 1000Hz) causes eye strain and headaches in a subset of people. Most people are not affected, but those who are find the symptoms consistent and repeatable.

How do I know if my monitor uses PWM?

Point your phone camera at the screen in video mode and move it quickly. If you see dark horizontal bands scrolling across the camera preview, your monitor uses PWM. For a definitive result, use a hardware photodiode or flicker meter.

What PWM frequency is safe?

Most sensitive people cannot perceive flicker above 1000Hz. Many modern monitors use 1000-3000Hz PWM or DC dimming (no PWM). Frequencies below 200Hz are the most problematic for sensitive users.

What is a flicker-free monitor?

A flicker-free monitor uses DC dimming instead of PWM to control backlight brightness. The voltage is reduced directly, eliminating the on/off switching cycle entirely. Look for TUV Rheinland flicker-free certification or the monitor manufacturer specifically stating DC dimming.