A flicker researcher reviewed our screen flicker guide

Our guide to screen flicker and PWM dimming is the kind of page people read when their eyes hurt or a new phone gives them headaches. We wanted it checked by someone who has done the research, not just read about it.

So we asked Professor Arnold Wilkins to review it. He is an emeritus professor of psychology at the University of Essex, also affiliated with the Department of Engineering at the University of Cambridge, and his research on flicker, striped patterns, migraine and photosensitive epilepsy goes back to the 1970s. Several of the studies our guide already cited were his.

He read the English text of the guide and of our refresh rate test, sent back detailed comments, and we rewrote parts of both. His name is now on both pages, with a short note on what his review covers. You can read more about him on his reviewer profile.

What we changed in the flicker guide

The old version was mostly right, but it blurred a few things together. Here’s what’s different now.

Four questions, kept apart. Can people see flicker? Does it cause discomfort or headaches? Does it slow down tasks like reading? And what don’t we know yet? The research answers each one differently, and most of it comes from room lighting, not screens. The new section, What the research shows, takes them one at a time.
Flicker can be seen at higher speeds than we said. When your eyes jump past a flickering light, you can catch a trail of separate copies, called a phantom array. Newer studies found that some people see it at much higher frequencies than older work suggested, in one study above 15,000 times a second. Those were best-case lab conditions, and the guide says so.
Low brightness matters. Many OLED phones dim the screen by flashing it in short bursts with long dark gaps in between. A 2024 lighting study found this kind of flicker easier to notice than flicker with equal on and off times. That fits with complaints clustering around reading in bed with the brightness turned down.
Reading. A 2024 study found that people read a little slower under flickering LED light than under steady light. The difference was small, and the light came from lamps, not phones, so the guide doesn’t stretch the result any further.
No made-up numbers. You’ll often see a figure for how many people are sensitive to flicker. Good data for that don’t exist, so the guide now says that plainly instead of guessing.
When to see someone. If headaches, eye pain, blurry or disturbed vision, or dizziness carry on after you put the screen down, the guide now tells you to see an optometrist, an ophthalmologist or your doctor.

What we changed in the tests

A guide about flicker is only half the job. Some of our tests flash or move fast on purpose, and the review made us take a harder look at them.

The refresh rate test now says what it can’t see. A browser can count how many frames your screen shows each second. It can’t see PWM flicker, because that happens in the light the screen gives off, which a web page never sees. The refresh rate test now says this right under your result, with a short table of what it checks and what it doesn’t.
A gentler flashing test. The flashing block in the ghosting test now starts at low contrast, below the level the web accessibility guidelines count as a flash. Full black and white needs a second yes. You can pause it with the space bar, a click or a tap, and it pauses on its own when you switch tabs. The warning now mentions migraine and headaches, not just seizures.
A heads-up before the benchmark. A few scenes in our performance test have fast motion, bright moving detail, dense dots or a flashing finale. The start screen now names them before anything runs, and the effects gallery tags them, so you can look at them first or slow them down in free play. The scored run itself hasn’t changed, so new scores still compare with old ones.

On WhiteScreen.tv, too

Professor Wilkins also reviewed the safety notes for the prank screens on our sister site, WhiteScreen.tv. Its guide to flashing prank screens now covers migraine and screen flicker, and the pranks that flicker have calmer options: a still version of the Glitch Screen, still or dark static for White Noise, and a tag on every tile that flickers.

What the review covers

A review credit can easily say more than it should, so here’s exactly what this one means. Professor Wilkins reviewed the science and the safety information in the English text of these two pages. He didn’t review our other pages, the translations or the code behind the tests. His review isn’t medical advice, and it isn’t an endorsement from his university.

If we change what one of these pages claims, we ask him to look again, and his name comes off until he has. Our editorial standards explain how expert review works here, and the full list of changes is in the changelog.

Thanks to Professor Wilkins for his time and his careful reading.