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Backlight Bleed Test
Backlight bleed is light leaking around the edges of an LCD panel, seen as bright patches on a dark picture. Dim the room, turn the brightness up, and open the black screen full-screen to see it.
Full-screen colour test
Clean the screen first so dust isn’t mistaken for a bad pixel. Start the test, then look over the whole screen on each colour. Click, tap or press → for the next colour, ← to go back, M to mark a pixel, H to hide the help and Esc to finish.
Or open one colour
marked
- x , y
Positions are in physical pixels from the top-left corner. Many warranties count bad pixels and where they are; note these before contacting the seller.
( of )
Press H to show this again.
Refresh rate and screen details
Keep this tab in front and don’t touch anything for 2 seconds while it counts frames.
- Refresh rate
- –
- Resolution
- Scaled size
- Pixel ratio
- Colour depth
Measured frames a second over frames, with dropped. If this is lower than your screen is sold as, check the refresh rate in your display settings and the cable.
Not enough frames were drawn. Keep this tab visible and try again.
Stuck pixel fixer
Flashes random colours very fast to try to free a stuck pixel. Drag the box over the pixel (or fill the whole screen), let it run, and check again with the colour test. It can’t revive a dead, always-black pixel.
Double-click or press Esc to stop
Testing the rest of your setup? Try the Keyboard Test, the Gamepad Tester, the Webcam Test or the Color Blind Test.
About the Dead Pixel Test
The dead pixel test fills your screen with black, white, red, green, blue and other solid colours, one after another, so a faulty pixel stands out against each of them. Grey and gradient screens show uneven brightness and colour banding, and the black screen shows backlight bleed. Switch on marking and click a bad pixel to record its exact position in physical pixels, which helps with a warranty claim. The page also measures your refresh rate and has a stuck pixel fixer that flashes colours to try to unstick a pixel. It works on monitors, laptops, TVs with a browser, tablets and phones, and nothing leaves your device.
How to use it
- 1 Wipe the screen so dust isn’t mistaken for a bad pixel.
- 2 Press “Start full-screen test”.
- 3 Look over the whole screen on each colour, then click or press → for the next one.
- 4 Press M and click any bad pixel to note where it is, then Esc to finish.
Frequently asked questions
How do I test for backlight bleed?
Dim or turn off the lights, set the screen to the brightness you normally use (or maximum to see the worst case), open the black screen full-screen, and look straight at the centre from your normal seat. Bright patches along the edges or in the corners are bleed.
What is the difference between backlight bleed and IPS glow?
Bleed stays in the same place and looks the same from any angle. IPS glow is a silvery or orange haze in the corners that changes or fades as you move your head. Glow is normal for IPS panels; heavy bleed may be a fault.
How much backlight bleed is normal?
A little bleed that you can only see on a black screen in a dark room is normal for most LCDs, including expensive ones. If it’s visible in films or games with the lights on, it’s worth returning the screen while you still can.
Can backlight bleed be fixed?
Sometimes it eases over the first weeks. Loosening the screws on the back of a monitor slightly, or massaging the edge of the bezel, can reduce pressure-caused bleed, but it risks damage and the warranty. A return or exchange is the safer fix.
What is the difference between a dead, stuck and hot pixel?
A dead pixel is always black, because none of its sub-pixels light up; it shows best on white. A stuck pixel stays red, green, blue or another colour and shows on black or on the other colours. A hot pixel is always white and shows on black. Stuck pixels can sometimes be fixed; dead ones usually can’t.
How do I check a new monitor or laptop for dead pixels?
Clean the screen, set it to its native resolution, run this test full-screen and look closely at every colour from about 30 cm away. Check as soon as it arrives, as most shops only accept returns for pixel faults within a short period.
How many dead pixels are acceptable?
It depends on the maker. Most follow the ISO 9241-307 class II rules, which allow a few faulty pixels per million. Some brands offer a zero bright-pixel guarantee. Note the count and position of each pixel this test marks, then compare with the maker’s pixel policy.
Can a dead pixel fix itself?
Rarely. A stuck pixel sometimes recovers on its own or with the stuck pixel fixer. A pixel that is black on every colour is usually a broken transistor and stays dead.
Does the dead pixel test work on phones and TVs?
Yes. On a phone or tablet, tap to change colour; on iPhone the page fills the screen without the Fullscreen API, so hide the toolbar by scrolling or use landscape. On a smart TV, open the page in the TV’s browser and use the arrow keys on the remote.
Is anything uploaded?
No. The colours are drawn by your browser and the marked positions stay on this page.
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