Monitor Flicker Test: Check Your Screen for PWM Flicker

Test 1: The slow-motion camera method (the reliable one)

A camera's sensor scans line by line, much faster than your eye refreshes. When a backlight pulses on and off, the camera captures the on and off moments as bright and dark stripes. Your eye smooths those out. The camera does not. That is why this is the definitive home test.

1. Drop the brightness to about 20%. PWM is deepest at low brightness because the backlight is dark for more of each cycle. Testing dim gives you the best chance of catching it.
2. Open slow-motion, not normal video. Switch your camera to its slow-motion mode and choose the highest frame rate available. Faster capture catches faster flicker.
3. Fill the frame with white. Open a blank white document or page on the screen under test, then hold the phone 20 to 30 cm away so the white fills the view.
4. Record a few seconds, then play it back slowly. Watch for horizontal dark bands rolling up or down the image. Bands that move through the frame are the signature of a pulsing backlight.
5. Climb the brightness ladder. Repeat at 50% and 100%. If the bands are strong at 20%, weaker at 50%, and gone at 100%, that is textbook PWM whose duty cycle rises with brightness.

Per-phone camera guidance

Any recent phone works. Higher frame rates catch higher-frequency flicker, so use the fastest mode you have.

What the stripes mean

Reading the result is straightforward once you know what you are looking at:

Test 2: The pencil test (quick check)

No slow-motion mode handy? Use a pen. In a dark room, turn the screen to a bright white image, hold a pen a few inches in front of it, and wave it quickly side to side. A steady display blurs the pen into one smooth streak. A pulsing display strobes it into several separate, ghostly copies, one for each flash of the backlight. It is not a measurement, but it is a fast yes-or-no hint before you reach for the camera.

Test 3: On-screen motion pattern (with a caveat)

The pattern below moves a bright bar across a dark strip. In a dim room, stare at one edge and let your eyes flick across to follow the bar. On a steady display it blurs into a smooth trail. On a pulsing display it can break into separate copies, the same stroboscopic effect as the pencil test.

Confirm with measured data

Two independent labs measure display flicker with photodiodes and publish the numbers, so you can look up your exact model instead of guessing:

• RTINGS monitor image flicker test measures flicker frequency at different backlight levels and flags whether a monitor is flicker-free.
• NotebookCheck PWM database ranks hundreds of laptops, phones, and tablets by measured PWM frequency. It notes that frequencies above roughly 500 Hz are generally fine for most people, while problems cluster below about 250 Hz.

If you cannot find your model, the camera test plus the brightness ladder is a solid substitute.

You found flicker. Now what?

If your screen pulses and you are sensitive to it, you have three honest options, ranked by how reliably they work:

1. Switch to flicker-free hardware. A display with DC dimming or measured PWM above 1,000 Hz is the durable fix. See our guide to flicker-free monitors.
2. Keep hardware brightness high, dim with software. Since PWM is worst at low brightness, keep the backlight near full and use a software overlay to darken the image instead. This avoids the deep low-brightness pulsing.
3. Raise brightness and soften the room. A free partial fix: nudge brightness up and add gentle ambient light so the screen does not need to blind you.

For the full background on why low-frequency PWM causes symptoms, who is most sensitive, and how OLED and LCD differ, read our PWM flicker and headaches hub. For the broader picture on screen comfort, see the digital eye strain guide.