Monitor Flicker Test

Press Go full screen on the one-pixel checkerboard, then look closely for shimmer or crawling.

Pattern Pick one, then go full screen.

What to look for

F goes full screen. Escape leaves.

Waiting for your browser

Reported size
Pixel ratio
Real pixels
Scaling

A page sees the signal the computer sends, not the panel. The patterns below show the rest.

One-pixel checkerboard, mid grey on black

One-pixel checkerboard, mid grey on black

Preview · enlarged so the lines show

Each pixel alternates with its four neighbours. An LCD keeps flipping every pixel’s voltage, and when the two phases are not quite equal this pattern shimmers or crawls. On a balanced panel it sits still as an even dark grey.

1 of 5

Click, tap or press the right arrow for the next one. The left arrow goes back.

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What to look for

What you see and what it means

What to change first

Next step Still and even? Now check each pixel lightsNext: check the screen runs at its full rate

All 13 patterns and checks

Flicker patterns 5

  • One-pixel checkerboard, mid grey on black Each pixel alternates with its four neighbours. An LCD keeps flipping every pixel’s voltage, and when the two phases are not quite equal this pattern shimmers or crawls. On a balanced panel it sits still as an even dark grey.
  • One-pixel lines, mid grey on black Grey and black columns, one pixel each. Some panels flip their voltage line by line rather than pixel by pixel, and they shimmer here while the checkerboard stays calm. Look near the edges too, where shimmer can be stronger.
  • Green and magenta checkerboard Each green pixel lights only its green part and each magenta pixel only its red and blue, so neighbouring colour parts alternate. A panel that looks still on grey can flicker on this one.
  • Two-pixel checkerboard, mid grey on black The same checkerboard with squares two pixels wide. It catches panels that flip their voltage in pairs of rows or columns, which a one-pixel pattern can miss. Stillness on all four patterns is the result you want.
  • Flat grey field for a phone camera An even mid grey with nothing to read by eye. It gives a phone camera plenty of light: point it at the screen with the brightness turned down and watch the camera's picture, not the screen.
Show all 13 patterns and checks (8 more)

What you see and what it means 4

  • Shimmer or crawl on the grey patterns The two voltage phases of each pixel are not quite equal, so every pixel pulses slightly. Close up, plain colours can seem to crawl too. Which grey pattern shows it hints at how the panel flips its voltage.
  • Shimmer only on green and magenta The panel is balanced for grey but not when neighbouring colour parts alternate. It is the same cause as grey shimmer, shown by a harder pattern, so note it down the same way.
  • Moving dark bands in the camera picture The backlight is being dimmed by switching it on and off. A phone camera reads its sensor one row at a time, so the off moments show as bands your eye does not see. Raise the brightness and look again.
  • The pattern looks flat grey The screen is being scaled. Something between the browser and the panel is resizing the picture, so one-pixel squares blur together and no shimmer can show. A panel that flickers would pass this test, so fix the scaling first.

What to change first 4

  • Set native resolution and 100 percent zoom Choose the resolution your display settings mark as recommended, and reset browser zoom. On a TV, turn overscan off in the picture size menu. Then check the checkerboard shows fine squares close up.
  • Write down which pattern shimmers Strong shimmer means voltages set inside the monitor are off, and a user usually cannot adjust them. Note the pattern and whether it is worse near the edges, for a return or a support ticket.
  • Raise the brightness Many backlights dim by switching on and off across some or all of their range. Turn the brightness up in steps and repeat the camera check. If the bands vanish above a level, keep the screen at or above it.
  • Reseat or swap the cable A whole picture that blinks, drops to black or sparkles is not what these patterns test. Check the connection first: push both ends of the cable in firmly, then try another cable or another port.

How this list was compiled: Written for this page. Every pattern is drawn by the page at exact device pixels. That an LCD holds its picture between frames, that it alternates each pixel's voltage between positive and negative ('polarity inversion') and that a small difference between the two makes pixels flicker, and that most LED backlights use pulse-width modulation in part or all of their dimming range, are from https://en.wikipedia.org/wiki/Flicker_(screen). That PWM dims a constant light by switching it on and off is from https://en.wikipedia.org/wiki/Liquid-crystal_display and https://en.wikipedia.org/wiki/Pulse-width_modulation. That a camera sensor reading rows one after another records fast bursts of light as artifacts is from https://en.wikipedia.org/wiki/Rolling_shutter. That strong inversion flicker means the monitor’s voltages are misadjusted and is probably not user-adjustable, that the test needs native resolution, and that flicker may be stronger near the edges, are from http://www.lagom.nl/lcd-test/inversion.php. All checked 2026-09-23. A web page cannot measure a backlight's flicker or its frequency: this page shows patterns and gives no number. Licence: own work

How it works

This screen flicker test shows patterns that make a faulty LCD shimmer. A still, even grey means the pixels hold steady. To catch a flickering backlight, turn the brightness down and film the flat grey field with a phone.

Read the full guide

Reading the patterns

Go full screen and sit close. Step through the four grey and colour patterns with the arrow keys or a tap. Each should sit still as an even field. Shimmer that stays at native resolution is in the panel, not the signal.

Screen flickering test with a phone camera

Choose the flat grey field and turn the brightness down. Point a phone camera at the screen and watch the camera's picture, not the screen. Then raise the brightness step by step and look again.

Questions and answers

Can a website measure screen flicker in Hz?

No. A browser cannot see the backlight or time its switching, so this page gives no number. It shows patterns you judge by eye, and a flat field for a phone camera, which can catch switching your eye misses.

Why does my monitor shimmer on a checkerboard?

Each LCD pixel keeps flipping between a positive and a negative voltage. If the two are not quite equal the pixel pulses, and a checkerboard lines the pulses up where you can see them. Strong shimmer means the monitor's voltages are misadjusted.

Why does my phone camera show no bands?

The brightness may sit above the range where the backlight switches, or the screen may dim by lowering its current instead, which does not flicker. Repeat the check at the lowest brightness before you decide.

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