What the dead pixel test is for
A dead pixel stays dark whatever colour is shown. A stuck pixel stays lit in one colour, usually red, green or blue. Both are easy to miss in everyday use and easy to spot on a plain, single-colour area. This test fills the entire screen with black, white, red, green, blue and grey in turn, so that every pixel has to show every primary colour at least once.
Checking for pixel faults is worth doing with a new monitor, laptop or phone while you can still return it, and before buying a used device. It also helps to distinguish a pixel fault from dust, a scratch or pressure marks.
The test runs entirely in your browser and needs no download. On a computer it switches to real fullscreen; on devices where the browser does not allow that, the colour area covers the whole page.
Step by step
- Clean the screen with a dry, soft cloth so that dust is not mistaken for a pixel fault.
- Set the brightness to a normal level and dim the room a little if you can.
- Press “Start screen test”. The page switches to fullscreen and shows the first colour.
- Look over the whole area including the edges and corners, first from your usual distance, then up close.
- Click, tap or press Space or the right arrow key for the next colour.
- Note the position of anything you find, then press Esc to end the test.
Common problems and fixes
Is it a pixel or dust?
Dust usually looks slightly blurred and moves when you wipe the screen. A pixel fault is perfectly sharp and stays in exactly the same place on every colour where it appears. Looking at it from a slight angle can also help: dust on the surface shifts against the image.
Fullscreen doesn’t start
Browsers only allow fullscreen after a click or tap, and some, such as Safari on the iPhone, do not support it for web pages. The test then uses the full page area instead. Hide the browser bars by scrolling or rotating the device, or use the browser’s own fullscreen view (F11 in Chrome and Firefox on Windows).
A bright spot or cloudy area appears on black
That is not a pixel fault. Bright patches at the edges of an LCD panel are called backlight bleed and are common to some degree. Dimming the brightness reduces them. Uneven areas on grey can indicate uneven backlighting.
A line of pixels is wrong
A whole row or column that fails usually points to a problem with the panel connection or the display electronics rather than individual pixels. Check the cable on an external monitor and contact the manufacturer if it persists.
Tips
- Black reveals stuck pixels, white reveals dead ones. Red, green and blue reveal subpixels that fail in only one colour.
- Use the grey screen to look for uneven brightness and dirty-screen effects.
- Take a photo of any fault with the colour still on screen. It helps when you contact a retailer or manufacturer.
- Check the manufacturer’s pixel policy before testing a new device, so you know what counts as a defect for a return.
- On an OLED phone, also look at black closely. OLED pixels are switched off on black, so a lit dot stands out clearly.
Frequently asked questions
Can a stuck pixel be fixed?
Sometimes a stuck pixel recovers on its own after a while. Tools that flash colours rapidly are sometimes suggested, but there is no guarantee. A dead pixel that stays dark on every colour usually cannot be repaired.
How many pixel faults are acceptable?
That depends on the manufacturer’s warranty and pixel policy, which differ from brand to brand. Check the documents for your device. Within the return period, the retailer may accept a return regardless.
Does the test work on my phone?
Yes. Tap to change the colour. On an iPhone, Safari may not allow real fullscreen, in which case the browser bars stay visible at the edges.
Is the test safe for my screen?
Yes. It only displays plain colours, like any other picture. It does not flash rapidly.
Why are there six colours?
Each pixel is made of red, green and blue subpixels. Black and white show whether the pixel works at all, the three primary colours show each subpixel on its own, and grey makes uneven brightness easier to see.
How do I end the test on a phone without a keyboard?
Tap through all six colours. A tap on the last colour, grey, ends the test and brings you back to the page.