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Red Screen Test

The red screen test floods your whole display with pure red — #FF0000, nothing else — so faults that hide behind normal content have nowhere to go. It is the fastest way to spot dead pixels, stuck pixels, OLED burn-in and LCD backlight bleed on a phone, laptop, monitor or TV. There is no watermark, no button and no text on the red, because anything drawn over the test surface is something you might mistake for a fault. Free, runs in the browser, nothing to download.

Tap the button above to flood the screen with pure red, then look closely: black specks are dead pixels, off-colour dots are stuck pixels, and faint ghost shapes are burn-in. Tap anywhere on the red — or press Esc — to come back.

Ready to check your display? It takes one tap.

Use the free Pure Red Screen →

What is a red screen test?

A pure red screen test fills every pixel of the display with the same value — full red, zero green, zero blue. On a working screen the result is one flat, completely even field of colour. Anything that breaks that evenness is a defect, and a single uniform colour is what makes it obvious: your eye is very good at catching one wrong dot in a plain field, and very bad at catching it in a photo or a web page.

Red is the most useful single colour to start with because it drives only one of the three sub-pixels in each pixel. A pixel whose green or blue sub-pixel is stuck on will announce itself immediately against the red, and the green and blue sub-pixels being switched off makes a dead (permanently black) pixel easy to see too. A solid red screen test is normally run alongside solid green, blue, white and black for a full sweep — red is simply the one that catches the most on its own.

How to run the red screen test

Running the red screen test online takes one tap and about a minute — there is nothing to install and no account to make. A little preparation is the difference between catching a fault and walking past it:

Open capsuletools.app/pure-red-screen/
Turn the screen brightness up and, if you can, dim the room — bleed and burn-in are far easier to see in the dark
Wipe the screen first, so dust and fingerprints don't get counted as pixel faults
Tap Tap for full screen. The browser goes full screen and the red covers everything — no toolbars, no buttons, no text
Look at the display from about 30 cm away, then sweep slowly across it, paying extra attention to the corners and edges
Tap anywhere on the red — or press Esc — to come back

The tool takes a screen wake lock while the red is showing, so the display will not dim or sleep part-way through the inspection. Everything happens in your browser: no file is uploaded, no account is needed, and nothing is stored.

What to look for

A red screen pixel test is mostly a matter of looking slowly. Four different faults show up against a solid red field, and each looks distinct once you know what you are after.

Dead pixels

A dead pixel gets no power at all, so it stays black on every colour. Against a full red field it reads as a tiny hard black speck that does not move when you tilt the screen or wipe it. That is all a dead pixel test online really amounts to: one flat colour, and your eyes. One or two dead pixels are common enough that most manufacturers' warranties tolerate them; a cluster is a genuine panel fault.

Stuck pixels

A stuck pixel still has power but is frozen at one sub-pixel value, so on red it appears as a green, blue, cyan or white dot. That colour change between test screens is exactly how a dead or stuck pixel test tells the two apart: a stuck pixel looks different on red than it does on green, while a dead pixel looks identical on both. Stuck pixels sometimes recover on their own or after cycling colours for a while; dead ones do not.

OLED burn-in and image retention

On OLED phones, laptops and TVs, elements that stay on screen for hundreds of hours wear their pixels unevenly and leave a permanent shadow. A flat red field is a good OLED burn-in test screen because the ghost shows up as a dull or slightly brownish patch in the shape of whatever caused it — a status bar, a navigation bar, a keyboard, a game HUD, a broadcaster's logo. If the shape fades after a few minutes of other content, it was temporary image retention; if it stays, it is burn-in.

LCD backlight bleed and clouding

On an LCD, light from the backlight can escape past the edge of the panel. Run the backlight bleed test in a dark room: bleed shows as pale spotlights at the corners and edges, and clouding as broad washed-out patches where the red looks pink and thin. A little is normal on IPS panels — large, bright, or asymmetric patches are a reason to send a new monitor back.

Red screen test on iPhone and mobile

On Android browsers and on iPad, the tool uses the browser's normal full-screen mode, so the red covers the entire display with no chrome at all. Safari on iPhone does not offer the Fullscreen API to web pages, so the red screen test on iPhone works slightly differently: the red fills the whole page instead, and scrolling up once pushes the address bar out of the way. The result is an unbroken red field with only the status bar remaining.

Phone screens are the most rewarding thing to test this way, because they are almost always OLED and almost always show something in the same place all day. Check the strip behind the status bar at the top and the area where the keyboard sits — those are where retention shows up first.

Frequently asked questions

What is a dead or stuck pixel?

A dead pixel receives no power, so it stays black no matter what the screen displays — on a red screen it looks like a tiny black speck. A stuck pixel still has power but is frozen on one sub-pixel value, so on a red background it shows up as a green, blue, white or black dot. The practical difference is that a stuck pixel changes appearance between colours, while a dead pixel looks identical on every one.

How do I check for dead pixels online?

Open the red screen test, tap the button to go full screen, and study the display up close from about 30 cm away. Any dot that is not the same solid red as everything around it is a suspect pixel. Because the whole test runs in the browser, you can check for dead pixels online with no download, no app and no account — useful when you are inspecting a monitor or phone you have just bought.

How do I check for screen burn?

Fill the display with one flat colour and look for a faint ghost image that does not belong there. A solid red field makes retained shapes — a status bar, a navigation bar, a game HUD, a channel logo — visible as slightly darker or discoloured patches. Burn-in stays in the same position when you move the screen or scroll, which is what separates it from a smudge or a reflection.

What does OLED burn-in look like?

On an OLED burn-in test screen it looks like a faint, permanent shadow of whatever was displayed for long periods — most often the phone status bar across the top, the keyboard area, or a HUD from a game. On red it usually reads as a slightly dull or brownish band rather than a sharp outline. Short-lived versions of this are image retention and fade after a few minutes; true burn-in does not.

How do I test for backlight bleed?

Backlight bleed is easiest to judge in a dark room. Run a full-screen solid colour and look at the edges and corners: bleed appears as pale, washed-out patches or spotlights where the backlight escapes past the panel. Red works well for this because any unevenness shows as a lighter pink area. Some bleed is normal on IPS panels; large bright patches are not.

Does the red screen test work on iPhone?

Yes. Safari on iPhone does not support the Fullscreen API, so instead of switching to true full screen the red fills the entire page. Scroll up once to push the address bar out of the way and you get an unbroken red field for the red screen test on iPhone. On iPad and on Android browsers the normal full-screen mode is used.