How to Test a Screen for Dead Pixels, Stuck Pixels and Backlight Bleed
When you get a new phone, laptop or monitor, or buy one second-hand, it is worth checking the screen before the return window closes. Small faults such as a single dead pixel or a glow in one corner are easy to miss in everyday use but obvious on a solid background.
This guide explains the common faults and what they look like, gives a step-by-step test with full-screen colours, and covers what to do if you find something. It ends with how to run the test with Tint.
What you are looking for
Each pixel on a screen is made of red, green and blue sub-pixels. Most faults come from one of these not behaving, or from the light behind the panel:
- Dead pixel: a pixel that stays dark. It shows up as a black dot on white or bright colours.
- Stuck pixel: one or more sub-pixels stay lit, so the dot is a fixed colour such as red, green or blue. It is easiest to see on black or on a contrasting colour.
- Hot pixel: all three sub-pixels stay lit, giving a bright white dot that stands out on black.
- Backlight bleed: on LCD screens, light leaking around the edges or corners, visible as a glow on a black screen in a dark room.
- Uneven brightness or tint: patches that look darker, cloudy or a slightly different colour on a plain white or grey screen.
- Burn-in or image retention: on OLED and some other screens, a faint ghost of something displayed for a long time, such as a status bar, visible on plain grey or colour screens.
Before you start
- Clean the screen gently with a soft, dry cloth, so dust is not mistaken for a pixel fault.
- Turn off night mode, blue light filters and automatic colour adjustments for the test.
- Set the brightness to maximum for the colour tests, and lower it later for the black test.
- Make the test page full screen so nothing else is on the display.
- Dim the room for the black screen test.
The test, colour by colour
Show each colour full screen for long enough to scan the whole display slowly, row by row. Look straight on, then from a slight angle.
- White: look for dark dots (dead pixels), patches and an overall tint.
- Black: in a dim room, look for bright dots (stuck or hot pixels) and glow along the edges and corners (backlight bleed). OLED screens should look completely black.
- Red, green and blue: a stuck sub-pixel shows as a dot that looks wrong on some of these colours and fine on others. A dead pixel shows dark on all three.
- Cyan, magenta and yellow: each combines two primaries, so they give a second look at sub-pixel faults and make colour shifts across the panel easier to notice.
A magnifying glass or your phone's camera zoomed in can help confirm whether a dot is on the screen or a speck of dust.
If you find a fault
- Note where it is and take a photo of the screen showing the fault on the colour that reveals it best.
- Check the seller's or manufacturer's returns and warranty terms. Many have a written policy on pixel faults that sets how many, and where, count as a defect.
- Contact the seller while you are still inside the return period, if you have one.
- Small amounts of backlight bleed are common on LCD panels. It is reasonable to ask whether what you see is within the manufacturer's normal range.
You may read that stuck pixels sometimes recover on their own or after displaying rapidly changing colours. Results vary, and dead pixels generally do not recover. Do not press hard on the screen, which can cause further damage.
Running a screen test with Tint
Tint includes a display test with eight full-screen colours:
- Open Tint in your browser and use the browser's full-screen option so the colour reaches the edges.
- Tap Test on the floating toolbar. The screen turns white, and a counter shows 1 / 8.
- Tap anywhere to move on to black, red, green, blue, cyan, magenta and yellow.
- Tap AUTO 3s to have the colours change every three seconds while you scan, and STOP AUTO to stay on one.
- To check a particular shade, such as a mid grey for uneven brightness, go back and use Pick to set it with the RGB sliders or a HEX code, for example 808080.
Tint cannot change your screen brightness from the browser, so set it yourself. The iPhone and Android apps can raise brightness to maximum automatically. For setting exact colours, see how to convert HEX colour codes to RGB.
Frequently asked questions
How do I check my screen for dead pixels?
Show full-screen white, black, red, green and blue one at a time and scan the whole display. Dead pixels show as dark dots on bright colours.
What is the difference between a dead and a stuck pixel?
A dead pixel stays dark. A stuck pixel stays lit in one colour, such as red, green or blue.
How do I check for backlight bleed?
Display full-screen black at high brightness in a dark room and look for glow along the edges and corners.
Can a stuck pixel fix itself?
Sometimes, but there is no guarantee. Dead pixels generally do not recover. Check your warranty instead of pressing on the screen.
Which colours does Tint's display test show?
White, black, red, green, blue, cyan, magenta and yellow, by tap or automatically every three seconds.