Screen Test

What this screen test checks

This screen test fills your display with carefully chosen patterns. It starts with an all-in-one test chart: coloured edges, grid and circles, colour bars, labelled grey steps, gradients, near-black and near-white patches, fine line patterns, small text and your screen’s resolution, all on one screen. Solid black, white, red, green and blue reveal dead, stuck and hot pixels. Grey screens show backlight bleed, clouding, bands and burn-in. Gradients and grey levels show banding and lost shadow or highlight detail. Text and fine lines show blur and scaling problems, a grid shows cropped edges, a bright square on black shows local dimming halos, and a moving block shows trails and smearing.

Everything runs in your browser: the patterns are drawn on your device and nothing is uploaded. It is a visual check, not a measurement, so your eyes are the instrument. The summary explains what each problem you report usually means.

How to test your screen

Before you start

Clean the screen first, so dust is not mistaken for dead pixels. Turn off automatic brightness, night modes (Night Shift, night light, eye comfort) and dynamic contrast, which change the picture while you look at it. Let a monitor warm up for 15 to 30 minutes, use its native resolution, and keep browser zoom at 100%. For the black step, dim the room: bleed and glow are much easier to see in the dark.

Quick check or full check

The quick check shows the test chart, then the four patterns that matter most when you buy or receive a screen: black, white, red-green-blue and grey uniformity. It takes about two minutes. The full check adds gradients, black and white levels, gamma, sharpness, geometry, blooming and motion, and takes about eight minutes. You can also open any single pattern from the list below the buttons.

Move freely between patterns with the arrow keys or by swiping; press H or Help at any time. Marking is optional: press OK if a pattern looks right or Problem to note what you saw, pick one or more symptoms, add a short note and mark the exact spot on the screen. If you mark at least one pattern, you get a summary at the end.

Reading your summary

When you finish, the summary lists every step with what you reported, shows a map of the spots you marked and explains each symptom: whether it is a defect or a normal trait of the panel, and what to do about it. Your result is saved in this browser so you can compare later runs, and you can copy a link to share it. Notes stay out of the link unless you choose to include them.

Dead, stuck and hot pixels

How to tell them apart

A dead pixel stays black on every colour: it is most visible on the white screen. A stuck pixel shows one fixed colour, such as a red or green dot, often because one of its sub-pixels is always on or always off. A hot pixel stays white or bright on the black screen.

Dust or a pixel?

Wipe the screen gently with a soft, dry cloth. Dust and specks move or disappear, a faulty pixel stays in exactly the same place. If you are unsure, take a screenshot: a dot that appears in the screenshot comes from the image, not from the panel.

Can a stuck pixel be fixed?

Stuck sub-pixels sometimes recover on their own after hours or days of normal use, or after the screen is turned off for a while. Tools that flash colours quickly over the pixel are popular, but there is no reliable evidence that they work, and fast flashing can be unsafe for people with photosensitive epilepsy, so TestrHub does not offer one. Never press on the panel: it can create new damage. Dead pixels do not recover.

Backlight bleed, IPS glow and uniformity

Bleed or glow?

Backlight bleed is light leaking around the edges of an LCD, visible on a black screen. It stays in the same place whatever your position. IPS glow is a soft brightening of the corners that changes when you move your head or step back. A little bleed is common, and IPS glow is a normal trait of IPS panels. Judge both at your usual brightness and viewing distance: photos taken with a phone exaggerate them a lot.

Clouding, bands and tint

On grey screens, a perfectly even image is rare. Slightly darker corners, faint vertical or horizontal bands (common on OLED panels at low grey levels) and small colour shifts are usually within normal limits. What matters is whether you notice them in everyday use: dark films, games, or large areas of one colour.

Testing a phone or tablet screen

Before buying a used phone

Ask to run the quick check on the phone itself, at maximum brightness with automatic brightness off. Look for dots on each colour, marks or patches on white, and shapes on grey. Then check touch with our touch screen test: a phone can display perfectly and still have dead zones.

OLED burn-in and image retention

Most modern phones have OLED screens, which can keep a faint trace of elements that stay on screen for a long time: the status bar, navigation buttons, keyboard or app logos. Look for these shapes on the 20% and 50% grey steps. A trace that fades after a few minutes of varied content is image retention. One that stays is burn-in, which is permanent.

Signs of a replacement screen

On a phone sold as OLED, black should be completely dark. A black that looks grey or glows in a dark room, a colour tint, lower brightness or uneven touch response can mean the original screen was replaced with a cheaper one. Ask the seller before paying.

Testing a new or used monitor

Run the full check as soon as you receive a new monitor, while you can still return it. Before blaming the panel for lines, flicker or missing edges, try another cable and another input: many problems come from the connection or the graphics settings. Keep your summary and take a photo of any defect at normal brightness, as evidence for the seller or the manufacturer.

Pixel defect policies and ISO 9241-307

Manufacturers do not all treat a few faulty pixels as a defect. Many refer to pixel fault classes from an international standard: the older ISO 13406-2, replaced by ISO 9241-307. These classes allow a small number of bright, dark and sub-pixel faults per million pixels, and a Full HD screen has about two million pixels. Some brands go further and promise zero bright pixels. Always read your product’s own pixel policy and the seller’s return terms: they decide what you can claim.

What a browser screen test cannot tell you

A web page cannot measure brightness, contrast ratio, colour accuracy, panel bit depth or input lag. Colours go through your operating system’s colour management, and the frame rate shown in the motion step only tells how often the browser drew frames, which usually but not always matches the refresh rate. Our methodology explains the limits of browser measurements.

Troubleshooting

The pattern does not fill the whole screen

On iPhone, Safari cannot hide its toolbars, so the area under them is not tested; landscape mode shows more of the screen. On a computer, check that the browser window is on the screen you want to test. On a TV, a missing edge in the geometry pattern means overscan: choose “just scan” or “fit” in the TV picture settings.

Fine lines shimmer or text looks blurry

The screen is probably not at its native resolution, or the browser or system is zoomed. Set the resolution to the recommended value and browser zoom to 100%.

Full screen closes by itself

Pressing Esc or swiping from the edge leaves full screen and pauses the check. Your progress is kept: choose “Resume check” to continue where you stopped.

Colours look washed out or tinted

Turn off night modes, colour enhancement and HDR mode on Windows, then run the check again.

My previous results disappeared

Results are kept only in this browser. Private browsing and clearing site data remove them.

Frequently asked questions

Is this screen test free, and is anything uploaded?

Yes, it is free and needs no account. The patterns are drawn by your browser, and results stay on your device unless you share their link.

How can I tell a dead pixel from a stuck pixel?

A dead pixel stays black on every colour. A stuck pixel shows one fixed colour. Stuck pixels sometimes recover; dead pixels do not.

Is backlight bleed a defect?

Some bleed is common on LCD screens. It is worth returning the screen if you notice it in normal use, at your usual brightness, not only in a dark room or in photos.

Can this test find OLED burn-in?

Yes. Look for faint shapes on the grey uniformity steps. If they fade after a few minutes of varied content, it is image retention; if they stay, it is burn-in.

Does it work on iPhone and Android phones?

Yes. Android phones and iPads can use full screen. On iPhone, the test fills the browser window but cannot hide Safari’s toolbars.

How many dead pixels are acceptable?

It depends on the manufacturer’s pixel policy and the pixel fault class of the screen. Check it, and the return period, as soon as you find a defect.

Can a website measure my screen’s brightness or colour accuracy?

No. Those need a hardware measuring device such as a colorimeter. A browser can only show patterns and estimate the frame rate.

Why is there no dead pixel fixer here?

Fixers rely on fast flashing colours, which can be unsafe for people with photosensitive epilepsy, and there is no reliable evidence that they work.