Screen Flicker Test

What is this tool?

Flicker is brightness that changes rapidly instead of staying constant. Many displays dim their backlight by switching it on and off very quickly — pulse-width modulation — and at low brightness that switching can become perceptible as eye strain, headaches or visible shimmer.

This test gives you steady fields (White, Gray, Black, Green, Blue) to observe, plus a temporal mode that alternates the field at a chosen rate so you can compare a known flicker against what your screen does on its own.

It is an observational tool. A browser cannot sample the backlight's actual duty cycle, so the page is explicit about that in its own limitations sections.

How to use it

1. Choose a modeStandard is a plain steady field. Brightness Focus walks through brightness levels, which is where PWM flicker usually appears. Temporal Focus alternates the field at a set rate. Precision runs for 60 seconds, because low-level flicker is easier to notice over a longer look than a glance.
2. Pick a patternWhite, Gray, Black, Green or Blue. Gray at low brightness is the most revealing for backlight flicker; White is best for judging overall steadiness.
3. Step down through the brightness levelsThe levels are 10%, 25%, 50%, 75% and 100%. Work downwards. PWM flicker on most displays is worst at low brightness, so 10% and 25% are the important steps.
4. Use the frequency control to compareTemporal Focus alternates at 2, 5, 10, 20, 30 or 60 Hz. Starting at 2 Hz — obvious flashing — and moving up shows you where your own perception threshold sits, which makes it easier to judge whether the steady field is really flickering.
5. Try the peripheral-vision checkLook slightly away from the screen while keeping it in view. Peripheral vision is more sensitive to flicker than central vision, so faint flicker often becomes obvious the moment you stop looking directly at it.

What the results mean

A steady field looks steady

No visible shimmer at any brightness level, including 10%. Either the display uses DC dimming or its PWM frequency is high enough to be imperceptible. Both are good outcomes.

Shimmer that appears only at low brightness

The classic PWM signature. The backlight is spending more time off at low brightness, so the duty cycle is easier to see. Raising brightness and lowering contrast, or enabling a flicker-free mode if the display has one, usually helps.

Flicker visible in peripheral vision only

Real and worth acting on. Peripheral sensitivity is higher, which is why some people get eye strain from a screen that looks fine when stared at directly.

Flicker that changes with the alternation rate

In Temporal Focus this is the test doing exactly what it was asked to do — it tells you about your perception threshold, not about a fault. Use it to calibrate your judgement of the steady fields.

Irregular flashing or dropouts

Not PWM. Intermittent blanking usually points at a cable, connector or power problem, or a graphics driver issue. Reseat the cable and try another port before suspecting the panel.

What it can detect

• Perceptible backlight flicker at low brightness levels
• Flicker that is only visible in peripheral vision
• Whether raising brightness removes the flicker — the usual PWM tell
• Irregular blanking that suggests a cable or driver problem rather than dimming
• Your own perception threshold, using the 2–60 Hz alternation ladder

Limits worth knowing

A browser can only report what the platform gives it. These are the honest boundaries of this page, so a result is never read as more than it is.

• The page ships three separate honesty sections — “Browser Test Limitations”, “When Specialized Hardware Is Needed” and “Caution: Rapid Temporal Content” — and its FAQ asks both “Can a browser detect PWM?” and “Can this test measure PWM frequency?” The answer to both is no.
• No frequency in hertz is measured or reported for your backlight. Measuring PWM needs a photodiode, an oscilloscope or a camera-based flicker meter. What this tool provides is a controlled field and a way to compare it against a known alternation rate.
• The alternation rate is limited by the display's refresh rate. A browser cannot alternate faster than frames are delivered, so the ladder tops out at 60 Hz — well below the frequencies at which real PWM usually operates.
• Rapid alternating content can trigger discomfort or seizures in people with photosensitive epilepsy. The page carries that caution explicitly. Stop immediately if you feel unwell, and skip the temporal modes if you are photosensitive.

Tips

• Test at night or in a dim room. Ambient light masks low-level flicker.
• If you find flicker at 10% brightness, try raising brightness and lowering contrast instead. That often keeps the same perceived image with far less flicker.
• Check your display's menu for a flicker-free, DC dimming or anti-flicker setting before concluding anything is wrong with it.

Troubleshooting

Related documentation

• DisplayDead Pixel TestFull-screen solid colours for finding dead, stuck and hot pixels by eye.
• DisplayScreen Uniformity TestA thirteen-step sequence across brightness, grey and colour fields, mapped to nine zones.
• DisplayBacklight Bleeding TestA pure black screen and a structured five-angle inspection for light leakage.
• DisplayRefresh Rate TestEstimate your display's refresh rate from frame timing, with a confidence level attached.
• DisplayDisplay FPS TestMeasure the frame rate your browser is actually delivering, with 1% lows and jitter.