Screen Flicker Test

Some displays dim the backlight by switching it on and off very quickly. These patterns give your eyes, or a phone camera, the best chance of noticing flicker, without claiming to measure it.

Set your display to low brightness, then wave a pencil quickly in front of this dark gray field. Several crisp copies of the pencil suggest flicker; a smooth blur suggests none. A phone camera pointed at the screen may show rolling dark bands.

Flashing light warning

The alternating patterns flash the whole screen between black and white. Do not use them if you are sensitive to flashing lights or have a history of photosensitive seizures.

Tick the box above to unlock the alternating patterns.

Human vision cannot see most PWM flicker. Many backlights switch hundreds or thousands of times per second, far faster than the eye can follow, so seeing nothing here does not mean your display does not flicker. Only a light sensor or an oscilloscope can measure it; these patterns are a visual aid. The rates shown for the alternating patterns are estimated from how often the browser draws frames, which can be lower than the display's refresh rate.

Runs entirely in your browser. Nothing is uploaded or stored.

How to use

  1. Lower your display brightness to 20 to 40 percent. Flicker from PWM dimming is usually strongest at low brightness.
  2. Press Start test and look at the gray field. Wave a pencil or your hand quickly in front of the screen. Multiple crisp copies of it suggest flicker; a smooth blur suggests none.
  3. Point a phone camera at the screen. Rolling dark bands in the preview are a sign of flicker.
  4. To try the alternating patterns, tick "I understand and want to see the flashing patterns" under the flashing light warning. They flash at a fraction of the refresh rate and let you see whether flicker at that rate is noticeable to you.

What this test can detect

  • Flicker that is visible to you at a given brightness level.
  • A rough indication of PWM dimming, using the pencil or camera method.
  • Whether you notice flicker at a few rates below your refresh rate.

Important

  • Human vision cannot reliably see flicker above roughly 60 to 90 Hz, and most PWM runs far faster. Seeing nothing does not mean the display does not flicker.
  • Only a light sensor or oscilloscope can measure flicker properly. This page is a visual aid.
  • The alternating patterns flash. Do not use them if you are sensitive to flashing lights. This page does not offer medical advice.

Questions

What is PWM dimming?
Pulse-width modulation dims the backlight by switching it on and off many times per second and varying how long it stays on. At low brightness the off periods get longer, which is why flicker is more noticeable there.